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June 8

Suppose that we discovered a large-ish asteroid on a collision course with the earth...

How close would it have to get to us before we could accurately calculate where the point of impact would be? --Kurt Shaped Box (talk) 01:46, 8 June 2008 (UTC)

Don't shoot until you can see the whites of their eyes. Hmm.. perhaps the point at which any changes in its speed or direction are found to be due mostly to the Earth's gravitational pull. The acceleration would theoretically have to be constant, or at least known at all times.--Russoc4 (talk) 01:53, 8 June 2008 (UTC)

Modelling orbits is mostly about having a large number of observations over a long time. Think of it this way. If an object is moving at a typical orbital speed of ~20 km/s, then a 1 m/s variation in that speed would lead to a change in the expected location of 150,000 km over 5 years, which would be a very noticable range of variation. If you have a long enough period of observations, you can be very precise about future orbital positions. For example 99942 Apophis, which will make a close approach in 2036, has it's predicted distance to Earth at that time nailed down to 3381 +/- 8 km (1-sigma). Dragons flight (talk) 02:44, 8 June 2008 (UTC)

Hi. 1950 DA, for example, has a roughly 1-in-300 chance of colliding with Earth in the 2800's, and we've calculated that the Earth's Atlantic Ocean faces the asteroid on its near pass/possible collision date. We don't know its exact chances yet, but we have observed its rotation enough to know this. Hope this helps. Thanks. ~AH1^(TCU) 16:49, 8 June 2008 (UTC)

Looking into the past

moved from talk page

If when we look towards the center of the Universe, we are looking billions of years into the past how is it, the Earth traveled to the distance it is now from the center of the Universe before the light from billions of years ago?

Did the matter that made up the Earth and the rest of the planets materialize in place?

Or did we actually travel faster than the speed of light?

Please excuse grammar and spelling.—Preceding unsigned comment added by 97.89.59.10 (talk) 01:29, 8 June 2008 (UTC)

Well we're obviously not anymore if we can see it. Not sure how that happened though. Probably we were quite close to those stars a looong time ago and space has been expanding at nearly the speed of light or something, so the light has been sloooowly catching up to us. So by the time it finally finishes its 1-inch trip by overtaking us, it's already billions of years old. I don't know, sounds wrong? --.froth. (talk) 03:32, 8 June 2008 (UTC)

There is no centre of the universe. When we say the universe is expanding, we don't mean it's all moving out from a centre, it's more like blowing up a balloon. The 2D rubber surface (ignore the fact that it's contained in 3D space, just think about the rubber) doesn't have a centre, each bit is stretching as you blow it up. If you draw some dots on it before you start you'll see those dots get further and further apart, but they never actually move, it's just the rubber inbetween them gets bigger. When all the matter was created shortly after the big bang, it filled the whole universe and has been spreading out as the universe expands ever since. This means bits of matter can be very far apart without having to have actually moved at all. --Tango (talk) 10:35, 8 June 2008 (UTC)

<----> Ok, even if there is not a center of the Universe, Which I’m not sure is true.

In order to look back in time and space to the Big Bang,

Would we have had to travel faster than the light in order to arrive here first in order to see it?

Is it possible the matter that makes us up arrived here before the light that was emitted from the Big Bang arrived.

could that be possible unless we actually traveled faster than that light, right?

I mean according to the rules; matter can not travel faster than light, so the light that was emitted then would have been at this point in time/space way before we arrived at this point in time/space right?

Please help me understand the logic.

Again please excuse grammar and spelling

<------>

See inflation (cosmology). Yes, the universe grew faster than the speed of light for a microscopic fraction of a second during the Big Bang. As a result, we are only now seeing light from matter we were next to previously (though at that time, none of the current matter had yet condensed). It is also worth noting that the cosmic microwave background, i.e. the "light of the big bang" actually was created ~3 minutes after the "bang", so that light comes from after we were seperated. Also see: Timeline of the Big Bang. Dragons flight (talk) 21:10, 8 June 2008 (UTC)

It's not true that the universe expanded faster than light during the inflationary epoch. Depending on how you define "expanding faster than light", either the universe never expands faster than light or it always expands faster than light; there's no definition that singles out the inflationary epoch. -- BenRG (talk) 23:27, 8 June 2008 (UTC)

(ec) The ideas of expansion of space, seeing "old photons" that are only now arriving to us, etc. comes up fairly often on the Science Ref-Desk. Here's a recent discussion focussing on how things can be further away than conventional "object at speed-of-light" would suggest: Wikipedia:Reference desk/Archives/Science/2008 March 26#Faster than light/Big Bang question. Not a direct answer to your question (which I don't fully understand), but something that may clarify some general/related ideas. DMacks (talk) 21:18, 8 June 2008 (UTC)

Actually, the CMB was released about 400,000 years after the big bang. You were close. ;) --Tango (talk) 21:33, 8 June 2008 (UTC)

The photon epoch begins at 3 minutes, the last scattering event (and end of equilibrium) came a few hundred thousand years later, but I think arguing that point is splitting hairs about what you mean by light created by the big bang. Dragons flight (talk) 21:49, 8 June 2008 (UTC)

We can see light from the early universe because the universe is homogeneous. The primordial fireball that emitted the light filled the whole universe, and the light that it emitted also filled the universe, and it still does, there being nowhere else for it to go. Cosmic inflation is the currently favored explanation for the homogeneity, but there's too little evidence at this point to say whether it's correct. -- BenRG (talk) 23:27, 8 June 2008 (UTC)

This is weird, and maybe I'm reading things wrong, but I believe you're all answering a question that wasn't asked and possibly even explaining them wrong...the way I'm reading the OP's question is "Why can we see into the past by looking at light from far away objects?" The answer is: Because the speed of light is finite instead of infinite. An easier example to understand is sound and the echo effect. When you shout at a large cliff, there is a delay between when your voice is projected and when it comes back as an echo. That time delay is due to the finite speed of sound. In fact, if you knew the speed of sound and the distance to that cliff you could calculate how long it took for your voice to get there (or knowing time you could calculate distance). In the same way, because we can determine the distance to the star using astronomical observation techniques, and knowing the speed of light and the fact that it is constant in the universe, we can determine how long ago the star emitted that light. EagleFalconn (talk) 14:13, 9 June 2008 (UTC)

Lunar Module Ascent Stage

A rocket launch on Earth is a jarring event even for a spectator. The sound and the fury of getting even a modest payload to Earth orbit is simply awesome. The scales involved seem overwhelming.

Why is it that a Lunar Module's Ascent Stage taking off for lunar orbit ( youtube link[1]) seems like such a walk in the park? It's not hundreds of feet tall, just 12. It only weighs as much as 5-10 cars. No ground crew required, no days sitting on a launch pad prepping. No drama whatsoever. Shouldn't the theatrics be 1/6th as much as they are on Earth? Sappysap (talk) 02:51, 8 June 2008 (UTC)

Well, it was just a vehicle to get the astronauts up into orbit (a few hundred miles?), not all the way to the Moon, so they didn't need much life support equipment. It also didn't have to overcome our stronger gravity, plus there was no air resistance or weather to worry about. For all these reasons, it didn't have to be as humongous as the Saturn V. Besides, who says there wasn't a lot of prep work anyway? Clarityfiend (talk) 03:25, 8 June 2008 (UTC)

It's not strictly proportional because you also need more fuel to lift the additional fuel, and more fuel to lift that extra fuel, ad infinitum. So, the higher the force of gravity, the larger percentage of the rocket that must be fuel. A chemical fuel rocket would hit some limit where it could never even achieve orbit from a planet with gravity above a certain level. (I wonder what that point would be ?). StuRat (talk) 14:16, 8 June 2008 (UTC)

Let's do some math to illustrate my point. If we say some type of fuel has enough energy so 10 lbs of fuel can lift 100 lbs of cargo into lunar orbit from the Moon, we would then need 60 lbs of fuel to lift that cargo into Earth orbit from the Earth, before we take into account the fuel needed to lift the fuel. Now, the 10 lbs of fuel would require 1 lb of fuel to lift, and that 1 lb would require 0.1 lb of fuel, for a total fuel weight of 11.1111... The 60 lbs of fuel would require 36 lbs to lift and that would require 21.6 lbs, etc., for a total fuel weight of 150 lbs. Note that the ratio between 150 lbs of fuel and 11.1111... lbs is 13.5:1, far more than the 6:1 ratio of gravity. This effect gets even worse when using fuels with less energy to mass.

So, we have the following reasons so far:

1) This "compounding effect" of fuel weight.

2) Only going to orbit versus escape velocity.

3) Air resistance.

4) The much lighter payload. StuRat (talk) 14:34, 8 June 2008 (UTC)

Don't forget the other implications of having no air resistance on the Moon. The lander is not required to have an cylindral, aerodynamic shape, so it doesn't need to be supported prior to launch while on the platform. Tail fins and other stablization systems are also not needed. On Earth, a rocket's exterior must be at least strong enough to withstand the air pressing on it. I'm not sure whether the casing adds significant weight to the craft, but no such strong structure is required on the Moon. --Bowlhover (talk) 15:59, 8 June 2008 (UTC)

Energy to orbit (neglecting air resistance) in terms of the central mass, M, radius of the object, R, and altitude to orbit, h, is approximately proportional to $M{R+h \over Rh}$. The mass of the moon is 7×10²² kg, versus 6×10²⁴ kg for the Earth. The radius of the Earth is 6370 km, versus 1740 km for the moon. And lastly you need ~180 km altitude to clear the Earth's atmosphere, versus only 20 km for the moon (to clear the mountains, though Apollo actually used 100 km).

Equating terms, you can see that for a given orbiter mass in order to get to orbit the moon you need only 1% as much energy as you do to orbit the Earth, mostly due to the Moon's greatly reduced mass. Since energy is basically proportional to fuel, you can do with far less fuel on the moon than on the Earth. And that's before considering air resistance, booster weight, and everything else one needs at Earth that you don't need at the moon. Dragons flight (talk) 17:17, 8 June 2008 (UTC)

That doesn't seem right; you should get 0, not infinite, energy as $h\rightarrow 0$. Just comparing the gravitational potential energy at R and $R+h$ gives me ${\frac {Mh}{R(R+h)}}$, giving 1.8% as much for the Moon/20km as for the Earth; is that what you meant? --Tardis (talk) 17:10, 9 June 2008 (UTC)

help-- i need some support in my research

hello great brains!!! i am trying to prove reflection of electromagnetic waves from metallic surfaces using basic principle of physics.does any one knows that is the proof going to be unique or it has been already done.actually i am trying to provide a firm reason for reflection of electromagnetic waves,in opposition to hypothetical proof provided by hugens.kindly help me that to which university would entertain such proofs.such that it gets recognized.

Reveal.mystery (talk) 2nd year Mechancal Engineering student India. —Preceding unsigned comment added by Reveal.mystery (talk • contribs) 03:34, 8 June 2008 (UTC)

I'm sorry but I don't understand the question. What are the "basic principles of physics" you're starting from? Maxwell's equations? Quantum electrodynamics? String theory? In at least the first two cases it's already been done. Why do you want to do this? —Keenan Pepper 04:00, 8 June 2008 (UTC)

I think what Reveal.mystery really asks is, "why does Huygens–Fresnel principle hold for the electromagnetic waves, and what fundamental principles of modern physics does it follow from?". Well, as Keenan said, if Maxwell equations are basic enough then, yes, it follows from them almost trivially. Simply assume the incident perturbation in electromagnetic field to be a harmonic plane wave (see equation in article if unsure what it is), and solve either numerically or analytically, whichever you like best. Play with shapes of obstacles and their dielectric constant to get the feeling for how the waves interact with surfaces and edges; this is not always easy analytically, so I would recommend using MATLAB. Now, on the other hand, if you are asking where Maxwell equations are coming from, then things really become much more complicated. First and foremost, there is a chicken and egg relation between special relativity and classical electromagnetism. And I really suggest you look no further than that at least until you are well familiar with the latter two. Hope this helps. --Dr Dima (talk) 06:09, 8 June 2008 (UTC)

I have moved the following new question here as it appears to be a continuation of this question. SpinningSpark 12:47, 8 June 2008 (UTC)

many many thanks to active wikipedists for their support. let me explain what actually i tried for: considering the wave nature of em waves i considered the interaction of the magnetic component of the wave with the metallic surface.now further on by applying lenzs law i propose the generation of an opposite directioned current in the plate.the interaction of the orginal and the field generated by lenzs law finally proves my point.

please helpme so that i may further more proceed in this area.basically i require it to be recognized by some university professor or any journal.since the subject dosent pertains to my branch ,such recognition would help me in my resume for my gre(M tech) interview.

Reveal.mystery (talk) 2nd year,Mechanical Engineering student (email removed per Ref Desk guidelines) india —Preceding unsigned comment added by Reveal.mystery (talk • contribs) 12:38, 8 June 2008 (UTC)

See Heinrich Hertz. He did the experiment you describe in 1886 and showed that electromagnetic waves can be reflected. You could experiment with it using a small dipole transmitting antenna, receiving antenna, and a transmitter and receiver, with a means of measuring signal strength, perhaps by measuring the AVC voltage in the receiver. I have read of physics demonstrations using the RF output (often US channel 3) from a video cassette recorder, with a small dipole antenna, and the same channel input on a TV receiver connected to a similar antenna. See [2] , [3] , [4]. Edison (talk) 19:28, 9 June 2008 (UTC)

I had to this as homework early last decade. To solve the Maxwell's equation you have to put on a few extra constraints, such as no electric field parallel to the surface of the plate. Electric charge can only travel on the surface of the plate. Lens's Law is already included in the Maxwell's equations. Graeme Bartlett (talk) 21:34, 9 June 2008 (UTC)

IF IT IS ALREADY DONE BY HERTZ .LET US DISCUSS WHETHER I AM CORRECT OR NOT .(sorry for caps). Consider the interaction of an electromagnetic wave with a flat metal surface ABCD.consider the wave to be incident along MN and reflected along NO.point of reflection being N. • According to the figure given above we consider a plane wave front of a electromagnetic wave which could be easily represented by a right handed system of axes. the wave propagates along z axis hence the wave propagation vector points along positive x axis.let us assume when the electromagnetic wave strikes the metalsurface at N with magnetic component along Z axis and the electric component along y axis.the dotted rectangle shows a small part of the metal.which we have used to represent the eddy current generated by em eave and the opposing current due to lenz's law as shown in figure.i had studied about the phase change of an em wave by 90 degrees on reflection from a rigid surface .i suppose phase chancge to be as such represented in figure.any em expert wikipedist pay some attention on my research.

Reveal.mystery mech engg student india

(talk)

Cancer screening

Does cancer screening refer only to the search for extant disease, and not individuals at risk from disease but that don't actually have it or can the term be used to encompass both? From my brief search it seems that the term is used to cover the search for existing disease only (even if in the early stages) so the ability to predict development of disease may not be inferred from the term. ----Seans Potato Business 11:26, 8 June 2008 (UTC)

You screen only for actual conditions, not for predispositions. If, for example, one tests a population for a gene that predisposes to cancer (say BRCA1), you're screening for the gene, not for cancer. - Nunh-huh 11:52, 8 June 2008 (UTC)

I think you're being too strict about the usage of "screening". In the US, pregnant women are routinely given prenatal screening for certain conditions of the fetus (such as Down's syndrome and spina bifidia). The screening detects elevated risks associated with certain conditions but does not give definitive diagnoses. In fact, the article on triple screen says:

The test is for screening, not for diagnosis,[4] and does not have nearly the same predictive power of amniocentesis or chorionic villus sampling.

--71.162.233.218 (talk) 13:46, 8 June 2008 (UTC)

Not too strict at all, they are screening for conditions that actually exist - but with imperfect tests. Nearly all screening tests need followup tests for diagnosis, because by their very nature, screening tests will have false positives. - Nunh-huh 03:01, 9 June 2008 (UTC)

Weather forecast

I'm not happy with current forecasts. I'd also like:

1) The predicted time of the highs and lows, and better yet a graph of predicted temps throughout the day.

2) A humidity forecast in a form similar to that listed above.

3) A wind speed forecast similar to that listed above.

Does anybody know where I can get such data ? StuRat (talk) 12:36, 8 June 2008 (UTC)

It might help if you said where you are (ie which country). And also what you are currently looking at. SpinningSpark 13:28, 8 June 2008 (UTC)

I'm in the US (Detroit) and use an Internet site for ad-free weather: [[5]]. I also can get forecasts for the temps every 3 hours or so from digital TV station 4-2, but only for the current day. StuRat (talk) 13:49, 8 June 2008 (UTC)

Have you looked at the NOAA site for your area[6] ? I didn't check if it meets all your spec but its a lot more than what you have already. Here's the link to their front page in case I got your local area wrong [7]. SpinningSpark 14:34, 8 June 2008 (UTC)

That works. I found their "tabular forecast" is what I want: [8]. Thanks ! StuRat (talk) 14:45, 8 June 2008 (UTC)

Hi. I live in Canada, and I can find a way to get all three. Here, The Weather Network[9] gives us hourly forecasts. As for hourly humidity and wind forecasts, The Weather Network gives us that every quarter part of the day, but I can also get it at Cleardarksky, although the measurements are vague. Hope this helps. Thanks. ~AH1^(TCU) 16:53, 8 June 2008 (UTC)

Thanks for the answers so far. Does anyone know of a weather forecast given as a graph ? StuRat (talk) 12:48, 9 June 2008 (UTC)

You've already tried the hourly weather graph tab[10] on the NOAA site right? What is missing there that you need? SpinningSpark 19:37, 9 June 2008 (UTC)

No, I hadn't found the graphs, only the tables. That looks good, except that it's for Detroit, Illinois instead of Detroit, Michigan, and I'm not sure how to change the city. StuRat (talk) 03:15, 10 June 2008 (UTC)

Ok, I figured out how to change the city, but, geez, that site's a real bi*** to navigate, isn't it ? I expected to be able to just pick on "Detroit IL" and type in "Detroit MI", but it's never that simple, is it ? StuRat (talk) 03:49, 10 June 2008 (UTC)

doh - sorry for the crap geography on my part, not my country. The easiest way I found to navigate that site is to start at the top level of weather chart http://www.weather.gov/ then click on the map on the area you want then repeatedly do that through (I think) three levels till you come down to a city. Then click on the type of data you want, which in your case is hourly weather graph. Hope that helps. SpinningSpark 02:39, 12 June 2008 (UTC)

That seems to work. It sure doesn't seem very intuitive, though. I expected to select the type of forecast (hourly graph), and then type in the city and state. StuRat (talk) 04:46, 13 June 2008 (UTC)

Wing layout

Why do most planes have only two wings?

Why layouts with double or three wings on each aren't more common?

And what about having a set of short wings stapled - not broader as the plane - over each other until the plane gets enough drag to fly? GoingOnTracks (talk) 12:53, 8 June 2008 (UTC)

See Biplane#Advantages and drawbacks to biplane designs. Xn4 13:31, 8 June 2008 (UTC)

We don't seem to have anything explaining the unpopularity of tandem wing designs, though. Algebraist 13:32, 8 June 2008 (UTC)

The unpopularity of tandem wing might be explained by its increased stability, which surprisingly, is not always desirable. Certainly for fighter aircraft, maneuverability is king and stability and maneuverability are mutually exclusive. Also, if sufficient stability can be achieved by other means (high mounted wings, dihedral etc) why go to the expense of additional wings. Also some large commercial aircraft (eg Boeing 747) achieve distributed CL (the reason for tandem wings increased stability) by means of the lifting body effect. SpinningSpark 14:05, 8 June 2008 (UTC)

Just one more point, the designer of the aircraft (Rutan Quickie) in the picture in the tandem wing article says he designed it that way so that it resembled the Stars Wars X wing starfighter. Probably not a lot of call for that outside of the kit plane market. SpinningSpark 14:17, 8 June 2008 (UTC)

One big factor seems to be the speed of aircraft. More wings means more lift but also more drag, both of which also increase with speed. Early planes went quite slowly, so needed all the lift they could get, and drag wasn't much of an issue. Current planes are much faster, so getting sufficient lift is possible from fewer wings, while keeping drag low is also more of an issue. StuRat (talk) 14:09, 8 June 2008 (UTC)

Excessive numbers of wings were included in some very early plane designs like the Phillips Multiplane [11] but triplanes are gone now, biplanes rares. Some canards seem like second sets of wings (Beechcraft Starship). Rmhermen (talk) 18:12, 8 June 2008 (UTC)

StuRat has it right - it's to do with drag (and mass). A single main lifting wing is usually the most efficient design to achieve a given lift with minimal weight and drag. In addition, the calculations required to design a multi-wing plane are much more complex, since there is a lot of interaction going on between the various wings (see the canard article for some of the trade-offs of using canards), so it's easier to optimise a one-wing design. — QuantumEleven 15:29, 10 June 2008 (UTC)

How do astronauts commit suicide?

Do they have some sort of suicide pill? Or are they expected to "sink" with the "ship"? —Preceding unsigned comment added by 88.6.118.85 (talk) 17:30, 8 June 2008 (UTC)

We are not a crystal ball - no astronaut has committed suicide in space yet. In fact, only three people have died while in space, the crew of Soyuz 11 due to a malfunctioning vent. (See also space accidents and incidents) While on Earth they have access to any suicide technique the rest of us do. Rmhermen (talk) 17:57, 8 June 2008 (UTC)

I think the original poster was asking about a situation where astronauts were stranded with no hope of rescue—would they be provided with means to commit suicide in lieu of 'waiting it out'? Obviously it hasn't happened yet, but it doesn't mean that no one has planned for it.

To reply to the question, as far as I can discern there is no record of NASA astronauts carrying suicide pills, nor is it likely that Soviet astronauts carried them. (Links to Q&A with shuttle crew, reference to Jim Lovell's book on the Apollo 13 mission.) Several astronauts and commentators note that there's no need to carry suicide pills on a space mission—venting the air from the capsule will do the job quite nicely, and loss of consciousness will occur in about fifteen seconds. TenOfAllTrades(talk) 18:09, 8 June 2008 (UTC)

The first person to perform a spacewalk, Leonov aboard Voskhod 2, secretly carried a suicide pill in case he had been unable to enter the spacecraft and had to be cut loose. --Bowlhover (talk) 18:50, 8 June 2008 (UTC)

Nonsense! How would he take the pill, considering he had a bloody big helmet on?--ChokinBako (talk) 11:30, 10 June 2008 (UTC)

I'm similarly puzzled, but it seems that Wikipedia is far from being the only source of the information. --Bowlhover (talk) 23:34, 12 June 2008 (UTC)

But is venting the air painless? How quickly can it be done? I doubt there's a "vent the air" button on the control panel. Wouldn't that be equivalent to a self destruct button? What if your buddies don't want to die with you? I think the original poster may have gotten the idea of a suicide pill from the movie Contact based on the novel by Carl Sagan. In it, Jodie Foster's character is given a suicide pill before she goes into the machine to take her to make contact with aliens. She is told that the pill has been given out to astronauts ever since the space program began, but it was never made public. She was told that the pill can be useful if she's stuck somewhere with no way to get back home, or trapped. Faced with the possibility of a slow painful death, the pill would put her out of her misery quickly and painlessly. She was also told that the pill is for all the reasons that they "could not think of". ScienceApe (talk) 18:53, 8 June 2008 (UTC)

That's fiction of course (rather a long drawn out one as I recall). I'd be more interested to know just how Leonov intended to administer his pill during the speacewalk given that's he'd be wearing his spacesuit.--Shantavira|^{feed me} 19:15, 8 June 2008 (UTC)

Nope, not drawn out at all. It was a very good movie. ScienceApe (talk) 02:45, 9 June 2008 (UTC)

Couldn't you just like take off your space helmet outside and suffocate?-- —Preceding unsigned comment added by Crystal eyes17 (talk • contribs) 20:59, 8 June 2008 (UTC)

I don't know about the Russian space program, but NASA spacesuits are designed in a way that the wearer can't possibly reach all the latches necessary to remove the helmet, and the assistance of a second astronaut is simply required to get out of it. Dragons flight (talk) 21:04, 8 June 2008 (UTC)

And even if you could get it off, the pressure would kill you before you suffocate since your blood (and all other fluids) would literally boil in the zero pressure of space.--十八 08:27, 9 June 2008 (UTC)

Well boil yes, but not "completely and instantly boil away" and not "astronaut swells up and explodes like in the cartoons":) Actually, the injury/death mechanisms don't seem related to the fluid-boiling issue at all See Vacuum#Effects on humans and animals for more info. DMacks (talk) 08:39, 9 June 2008 (UTC)

There's zero pressure outside your body, but inside, where the fluids are, there is still pressure supplied by your body. Assuming you don't try and hold your breath, which could result in your lungs exploding, death is usually by suffocation and if very quick (about 15 seconds to lose conciousness) - the vacuum almost "sucks" the oxygen out of your blood. --Tango (talk) 14:54, 9 June 2008 (UTC)

I'm pretty sure I heard of one instance where NASA astronauts were accidently subjected to a vacuum during training. I believe they passed out within 15 seconds before realizing anything was amiss, and without lasting injury. Someone may correct me if I'm wrong. Paul Davidson (talk) 13:50, 10 June 2008 (UTC)

I think they knew something was amiss. If memory serves, they reported their last memory before losing conciousness was of the saliva on their tongue boiling. Otherwise, you're right, they repressurised the room pretty quickly and the subject regained conciousness once the pressure got back up to a reasonable level, with no ill effects. I'm sure the incident is described on Wikipedia somewhere, I'll try and find it. --Tango (talk) 13:58, 10 June 2008 (UTC)

Found it: Human adaptation to space#Unprotected effects. Once again, we find that Wikipedia has an article on everything! --Tango (talk) 14:03, 10 June 2008 (UTC)

Garbage into oil?

Was there an attempt to turn garbage or sewage into oil? ScienceApe (talk) 18:42, 8 June 2008 (UTC)

Discover magazine says yes. The company responsible is Changing World Technologies. Clarityfiend (talk) 19:42, 8 June 2008 (UTC)

Why isn't this done on a much larger scale? We have enormous landfills that can be turned into oil. ScienceApe (talk) 02:47, 9 June 2008 (UTC)

When I expanded the CWT article, I found that their particular method costs $80 to produce a barrel of diesel, so until recently, it wasn't very profitable. Besides, the stuff in landfills would almost certainly have to have metals and other inorganic material removed, further raising costs. Clarityfiend (talk) 02:52, 9 June 2008 (UTC)

I can't provide a reference, but I know that the one large-scale implementation of this process (discussed in our article on CWT) had significant problems, including being shut down temporarily for generating very strong odors. ike9898 (talk) 20:24, 10 June 2008 (UTC)

See List_of_solid_waste_treatment_technologies#Advanced_waste_treatment_technologies methods include pyrolysis Gasification#Waste_disposal Thermal depolymerization amongst others - food waste is popular, as is garbage. Sewage is a possibility but more likely to be treated by Sewage_treatment#Anaerobic_digestion (as it is very wet) making 'biogas' which can be made into oil. If you are still interested try Waste management and follow the links...87.102.86.73 (talk) 17:23, 9 June 2008 (UTC)

The worst case of food allergies and religious food laws

What are the worst known cases of food allergies combined with restrictive religious food laws? E.g., you are not allowed to eat certain foods, but you are allergic to most of the foods that you are allowed to eat. Furthermore, most of the non-allergic and legal foods are not available in the place that you live. -- Toytoy (talk) 19:03, 8 June 2008 (UTC)

Religious food laws rarely limit the diet that much. For example, kosher and halal (which are similar in scope) limit barely a fraction of the pantheon of foods we could eat. I can't imagine a situation where one would need to circumvent these laws in order to avoid eating foods to which we are allergic. Fribbler (talk) 23:00, 8 June 2008 (UTC)

There was a somewhat related case mentioned in the radio recently. Certain christian priests complained that they have to administer masses in towns far away from their home so it would be best if they could drive, but they also have to drink wine for celebratory purposes on the mass, which of course excludes driving. – b_jonas 09:36, 9 June 2008 (UTC)

It's possible to be allergic to alcohol. Both that and gluten intolerance can make Holy Communion difficult. I read (but have lost the link) that members of the congregation may take only one, but Catholic priests must take both the bread and wine. 81.174.226.229 (talk) 11:00, 9 June 2008 (UTC)

http://www.catholicceliacs.org/Bishops.html ? —Keenan Pepper 12:05, 10 June 2008 (UTC)

To be technical, there's no such thing as an alcohol allergy, in large part because the ethanol molecule is way too small to be recognized by the immune system. One can however, have an alcohol sensitivity, which something else entirely. I can't find a specific reference to this on Wikipedia, but Mayo Clinic does a pretty good job. – ClockworkSoul 14:33, 10 June 2008 (UTC)

Let me add on to my statement a bit: there seem be be a number of reliable sources that suggest alcohol allergies do exist but are very uncommon. I'm more than a little skeptical, but I should at least acknowledge them. – ClockworkSoul 14:39, 10 June 2008 (UTC)

If you haven't come across it already, you may be interested in this [12] which mentions several case studies Nil Einne (talk) 18:38, 10 June 2008 (UTC)

Actually wikipedia covers Alcohol flush reaction and Alcohol tolerance resonably okay, which appears to be what the Mayo Clinic link is referring to. I'm not sure about alcohol allergies however. BTW, people with the alcohol flush reaction are unlikely to be trouble by receiving communion since the amount consumed is so low, it's unlikely to cause any problems. Nil Einne (talk) 18:35, 10 June 2008 (UTC)

Actually I was referring to the way my Dad's cousin vomits if a sauce contains alcohol which hasn't been completely evaporated by cooking, which may not be a proper allergy but doesn't sound like a mere tolerance issue. 81.174.226.229 (talk) 09:16, 11 June 2008 (UTC)

Rubber

Does all rubber contain latex? —Preceding unsigned comment added by 76.125.70.46 (talk) 20:01, 8 June 2008 (UTC)

In the area of rubber, latex does not indicate the contents of the rubber. It indicates that the rubber has not been vulcanized. -- kainaw™ 20:38, 8 June 2008 (UTC)

Latex is a pretty slippery term; its meaning depends quite a bit on context. Our article includes a fuller description of the different meanings. People who have a latex allergy are sensitive to natural rubber; they're likely not bothered by latex paint (which contains acrylic polymers). Generally – but not always – so-called 'latex rubber' is not vulcanized.

Synthetic rubber can be manufactured using a variety of compounds, many of which bear little resemblance to the ingredients of natural latex. Finally, the pedants will point out that 'latex' describes an aqueous emulsion; 'rubber' is what you get after the latex dries. Confused yet? TenOfAllTrades(talk) 15:54, 9 June 2008 (UTC)

Strange hypnagogic sensations

Sometimes when I'm just falling asleep, I experience a strange sensation -- it feels like my body is being distorted, changing in size or becoming stretched and compressed. It's not painful, but sort of dizzying and disorienting. This often accompanies the usual sensation of floating or falling, and sometimes sleep paralysis occurs at the same time. Is this a documented phenomenon, and what could its psychological or physiological basis be? 69.111.189.55 (talk) 21:45, 8 June 2008 (UTC)

Well, from your subject heading I guess you know about Hypnagogia... the article doesn't describe your experience exactly, but it seems in keeping with the broad set of weird things that happen in that state. Other than that, I don't know. --Allen (talk) 01:24, 9 June 2008 (UTC)

Wow. I used to feel that way often when I was a child and teen. I had forgotten all about that until I read this. At the time it was a bit disconcerting and I didn't know if it was something physiological or if it was all in my mind. My memories of the experience really don't sound anything like what is described in the hypnagogia article. It was more like my sense of scale was all weird; like my body was flattening, or if I closed my eyes I could see/feel in the blackness a perfect line, and I could let myself fall partly into it in a sense. At others it was like my fingers were huge, and it was a wonder I could move them. It is a very hard thing to describe. I don't think I could have then, and obviously I'm not doing a very good job of it now.

I think such sensations usually did happen when I was going to sleep, but I can't tell you if that was the only time or not (it's possible it also happened at other times when I was at rest and had a chance to calmly observe my sensations--e.g. meditation). Maybe it has something to do with the growing process; I haven't felt that way in my adult years. Then again, my sleeping habits have changed significantly since then too.

Anyway, sorry for the non-answer. It was great to hear someone else express the same kind of sensations that puzzled me, and I hope my rambling might in some way help you too, even if it isn't anything close to an "answer". (Keep in mind I'm not giving advise; if this is something you are at all concerned about, consult a medical professional.) --Prestidigitator (talk) 04:37, 9 June 2008 (UTC)

The "huge fingers" sensation happens to me, too; I also lose track of what position my arms are in. Indeed, it's kind of a relief to know that I'm not the only person who has these weird half-dream experiences. 69.111.189.55 (talk) 02:23, 10 June 2008 (UTC)

I used to get it when I was a teenager too. That is when I started to get sleep paralysis, too. My hands would feel enormous but not heavy in any way, just really big. The sleep paralysis was a seperate thing, though, and I experienced it more and more as I got into and went through my 20s. Take a look at the article Kanashibari. --ChokinBako (talk) 11:26, 10 June 2008 (UTC)

June 9

Prevnar vaccine

Is prevnar equally effective in India?Does it make sense to give prevnar to an infant in india, as the cost here is quite something. —Preceding unsigned comment added by 203.112.84.138 (talk) 09:35, 9 June 2008 (UTC)

The concern here is whether Prevnar, a pneumococcal conjugate vaccine available since 2000 in the U.S., and recently (2006) introduced in India, (see here) is effective, since it was developed to protect against the seven serotypes of pneumococcus that are most prevalent in the U.S.

Prevnar protects against serotypes 4, 6, 9, 14, 18, 19, 23, which cause 80-90% of disease in young children in the U.S. In Europe, which has a significantly lower incidence of invasive pneumococcal disease than the U.S., these 7 serovars account for only about 70-80% of that disease. In India, the most common serotypes in children under 5 years were 6, 1, 19, 14, 4, 5, 45, 12, and 7, in that order. [13] So Prevnar would protect against 4 of the 5 most common Indian serotypes, but would not protect against 1 and 5, which are more common in developing countries, and together make up 29% of Indian isolates. Clearly, if the vaccine had been formulated primarily for Indian use, it would have included these serovars rather than 18 and 23; and equally clearly, the vaccine protects against serovars that cause significant amounts of disease in India. An article in Indian Pediatrics notes that 25% of all child deaths in India are from pneumonia, and estimates that 30-40% of these are from pneumococcal pneumonia, meaning that between 123,000 and 164,000 children under the age of 5 die each year in India of pneumococcal pneumonia. Vaccines with either ten or thirteen serotypes, including 1 and 5, are likely to be available in 2010. India meets the WHO’s criteria for countries where pneumococcal vaccination should be a priority for introduction. The risks and benefits in any particular case must be decided in consultation between physician and patient. Since the concern here seems to be financial risk: The cost in 2006 was Rs 3750 per dose plus taxes, and was not covered under the extended programme for immunisation in India. If it chose to, the Indian government could obtain the vaccine at a cost of between 15 and 30 cents (U.S.) per dose. [14]. The editorial cited asks the Indian Academy of Pediatrics to urge the government to develop a process and timeline for introducing pneumococcal vaccination.

- Nunh-huh 20:18, 9 June 2008 (UTC)

Hmm, the question is posed as asking whether administering a vaccine is advisable. Isn't that medical advice? With all due respect to the responder, shouldn't this post simply be removed? Franamax (talk) 06:35, 10 June 2008 (UTC)

A request for information is not a request for advice, even if one can imagine that that information may ultimately be used in making a medical decision. No advice has been asked for or offered. The main distinctions between the referenced section in our Prevnar article is that the answer here is a bit more detailed, accurate, up-to-date, world-centric, and referenced than it is there. It's hardly censorable. A medical advice request would have been: "Should I give my baby Prevnar?". That wasn't asked. What was asked is "Is Prevnar effective at preventing disease in Indian babies?" - Nunh-huh 07:16, 10 June 2008 (UTC)

I'm normally a medical advice czar, but would have to agree with Nunh-huh here. The response was clearly not medical advice and concentrated on things like the cost-benefit to India etc and didn't answer much on what on whether it's advisable for a person to vaccinate their baby, which would depend on many factors and clearly should not be answered on the RD for precisely that and other reasons Nil Einne (talk) 22:38, 11 June 2008 (UTC)

Tooth restoration

before one restores a tooth permanently with amalgam can one temporize with IRM till gingiva improves and better moisture control is achieved for tooth to be restored are there any guidelines for it.

Thanks tanya —Preceding unsigned comment added by Mtanya (talk • contribs) 14:16, 9 June 2008 (UTC)

Is this a homework question? If so, could I have your name so that I never visit a dentist who asks random Internet dweebs to do their homework for them? Thanks. --Sean 14:52, 9 June 2008 (UTC)

Harsh - everyone starts with no knowledge and acquires it through training/education. That they ask for information (perhaps due to laziness at homework, or out of genuine need of help) isn't an indicator of their future abilities in the dental field. Oh and re the Q - I have no idea at all, sorry. ny156uk (talk) 17:23, 9 June 2008 (UTC)

You may want to check out the wikipedia articles: Dental restoration, Temporary restoration or Dental restorative materials, specifically Indirect Restorative materials (which is what I presume you mean by IRM). Checking out the citations in these articles will surely point you in the right direction. Jdrewitt (talk) 20:48, 9 June 2008 (UTC)

In this day of eliminating mercury in the mouth, someone is still using amalgam?—Preceding unsigned comment added by Julia Rossi (talk • contribs) 07:35, June 10, 2008

Amalgam is used as standard in many places; in the UK, for example, most NHS fillings are amalgam (if anyone's lucky enough to have an NHS dentist). Amalgam has many advantages over the resin alternatives (which can be found by reading amalgam), for which reason many dentists still recommend it for some work. The main advantage of resin compounds is cosmetic; it is not as effective for restoration, as it fails much sooner, can leak, and eventually shrinks, leading to bacterial growth and continued decay; if they are not maintained and replaced regularly there is a greater risk of root canal problems. It is also less effective for restoring larger areas. In addition, it is more expensive (particularly at the clinics which tell you of the dangers of mercury amalgam and offer to replace all your fillings for you). As to the possible toxicity of mercury amalgam, the jury is still out. I've got some amalgam fillings. If I go mad because of them, I'll let you know.  :) Gwinva (talk) 03:52, 11 June 2008 (UTC)

Incidentally Amalgam (dentistry) needs work. In the controversy part, it says "The most recent source[citation needed] of controversy has been from a December 1990 episode of the CBS news program 60 Minutes". I added the fact tag but the problem is obvious. Other then the fact this is uncited, it seems dubious to me that the most recent source of controversy could be conclusively said to be a 1990 episode of 60 Minutes. Especially since it's unclear how much controversy this generated internationally and the same section also says "In recent years evidence of serious toxic effects, for instance 25 studies of 5821 patients reviewed in "Effects of Amalgam Removal on Health", by Mats Hanson, plus a later study by Wojcik, Godfrey, Christie, Haley (2006)". (One would think this 2006 study generated some controversy) Nil Einne (talk)

Mercury, and cosmetic dentists with an alleged mi$$ion. I guess it's the processing which is more dangerous given that the vapour is toxic, but maybe in its set state, not the same problem (as testified to by Gwinva's erudition : ). In the mercury article there's a more recent ref to controversy – activity re bans in Norway 2007-2008 and needs references. Julia Rossi (talk) 23:46, 11 June 2008 (UTC)

Psychological concept of your perception of others

I vaguely remember a psychological/philosophical concept from the anime Neon Genesis Evangelion, which was along the lines of your perception of other people - their personality, appearance, your understanding of their motives and such, essentially the version of that person which you hold in your mind, which stems from your memories and previous encounters with this person - could be considered, philosophically speaking, as valid a description of them as that person's actual existing self. Does this concept have its roots in any psychological theory? Thanks. --Sum0 (talk) 20:05, 9 June 2008 (UTC)

That sounds like philosophy, not psychology. I don't see any psychological about that. --Tango (talk) 21:38, 9 June 2008 (UTC)

It's not quite what you say but "projection" could come into it if it means your perceptions are actually subjective. Closer to it is the empathy phenomenon. Julia Rossi (talk) 07:31, 10 June 2008 (UTC)

I think the term you are looking for is representation, although the term is pretty general and can be applied much more broadly than your use, and our article doesn't give you much anyway. You may also want to look at identity; although this is about how we see ourselves and not others, understanding how you form notions of your own identity will help you understand how you judge and represent those around you to yourself. --Shaggorama (talk) 22:40, 15 June 2008 (UTC)

Enzymes that remove pet urine odor

I understand that certain "enzymes" can break down pet urine in carpets. Something about the enzymes consuming the bacteria. Supposedly the urine smell occurs as bacteria consume the urine. Enzymes are said to kill and or neutralize this activity and reduce or eliminate odor. My question is what exactly are the names of these enzymes ? _____ase I want to know so I can be sure the product I purchase will actually do the job. Thank You, 70.118.255.25 (talk) 23:33, 9 June 2008 (UTC)

I don't think your theory is correct. There are very few bacteria in urine, as it is both sterile initially and somewhat antiseptic. The smell is simply ammonia. Any chemical which reacts with ammonia to break it down into odorless components would work to control the odor. Since ammonia isn't a protein, it doesn't require an enzyme to break it down. 67.38.24.177 (talk) 03:08, 10 June 2008 (UTC)

I don't have a specific answer for the OP, but I want to address a couple of misconceptions in the answer above. First, there's normally very little ammonia in urine; instead, nitrogen is excreted as urea. Thus, fresh urine has very little odor. Certain bacteria produce urease, which will "split" urea and can produce ammonia as a by-product. I suppose it is possible to inhibit the ureases. Second, as this suggests, enzymes act on many molecules other than proteins.Scray (talk) 03:29, 10 June 2008 (UTC)

OP is right as least inasmuch as there is a product that digests or absorbs or renders inaccessible the nitrogen in cat-pee that bacteria feed on. They had to spray a bunch of it when I moved in a year ago - and she was such a nice girl who never even owned a cat, too. I'll try to ask one of the maintenance people next couple of days, but by all accounts, such a theory and product does exist. Franamax (talk) 06:13, 10 June 2008 (UTC)

Googling "pet urine odor" shows lots of (lame) home-remedies and several commercial products using enzymes. We can't recommend a single product, and you will really never get any single name of some particular enzyme that is the "right" one. They are all commercial products, you need to read the descriptions and customer reviews on various websites and figure it out. Reading through the links, there are two or three that I would try. If I can find out the particular product used for my case, I'll post it here. Franamax (talk) 06:30, 10 June 2008 (UTC)

The only practical information I would like to add; from having multiple dogs and cats peee in the house over many years. Be sure to never use any products with AMMONIA because it will enhance the animal(s) to want to add their urine to the situation. Male dogs and cats do their normal marking and cleaning with AMMONIA or ammmonia based products is marking the spot.

June 10

Feisty baby gull...

Has anyone else here ever seen a gull chick deliberately starting a fight with an adult bird - and winning? Today, I had the opportunity to observe a colony of nesting Black-headed gulls at close quarters in their natural habitat. I noticed that most of the gull pairs had built their nests on small salt marsh 'islands', meaning that space was at a premium. The gulls (being typical gulls) were of course bickering, squabbling and pecking each other constantly over minor territorial encroachments and airspace above the nest. What surprised me, however was to see one of the older chicks joining in.

This particular bird was about 2/3 adult size with partially-grown wing feathers, so he/she was probably about three weeks old, or so. Yes, this youngster was starting fights with any adult gull which came too close to his mother's nest. Not only was he starting fights, more astoundingly he was winning them too! While I was watching, he must've seen off about 15 intruders with his chest-puffed, charging pecks. He certainly wasn't staying on his side of the line either - more than once, he chased an adult gull all the way across the island and into the water with his heel-snapping, causing absolute pandemonium amongst the uninvolved sitting hens. I just can't understand why the adult birds were prepared to take that from a chick...

Oh yes, in answer to the question someone asked the other day - it seems that baby gulls of this species *can* and do swim. I saw birds that were no more than a couple of days old trying to swim away from their nests (much to the annoyance of the parent gulls, who would corral them back, scolding loudly). They seemed to be fully waterproofed too. --Kurt Shaped Box (talk) 01:59, 10 June 2008 (UTC)

That sounds like behavior typically associated with species that have ascribed social status. That is, the offspring of the "alpha pair" may have the right to push around others, even adults. Do gulls exhibit such a complex social pattern as this ? 67.38.24.177 (talk) 03:04, 10 June 2008 (UTC)

I don't think so but I can't say for certain. I'm not as familiar with this species as I am with some of the others. --Kurt Shaped Box (talk) 14:39, 10 June 2008 (UTC)

gravitational redshift

The Pound-Rebka experiment showed that gamma rays lost energy/frequency as they fell through the building, due to gravitational redshift. Only by moving the emitter downward relative to the receiver could the gamma rays be given enough (doppler) frequency to be absorbed. This diagram and relativity-common-sense would seem to support that "time" runs slower for things (like photons) undergoing acceleration.

But the gravitational redshift article (and general relativity) says that light originating from a stronger gravitational field will have longer wavelength when received by an observer in a weaker gravitational field. Redshift for deceleration now! Which is it? The former makes more sense to me.. like a pendulum, the left-right motion of the wave in the horizontal direction stays the same, but the wavefront moves faster due to acceleration from gravity. So a stationary observer sees "more wave" go by for each cycle.. a redshift. So which is it for falling light? Redshift or blueshift? .froth. (talk) 05:27, 10 June 2008 (UTC)

Blueshift. If you move deeper in a gravity well, then you gain energy. Since photons can't actually move faster, the way this is manifest is by their blueshifting to higher energy state. Dragons flight (talk) 05:36, 10 June 2008 (UTC)

Fans and heating/cooling

Two questions:

1. If I put my hand in front of a fan, I can feel lots of air getting blown out. But if I put my hand behind the fan, I can barely feel any air getting sucked into the fan. So where does the air getting blown out the front of the fan come from? It feels like there's way more air coming out then getting sucked in.
2. It's summertime, and for the moment, I'm in a house without an air conditioner. At night, when the temperature drops, the second floor rooms stay way hotter than the first floor rooms and way hotter (by 5 to 10 degrees Fahrenheit) than the outside environment. Presumably, what is happening is that all the hot air from the first floor is rising up to the second floor and then getting stuck in the second floor rooms without being able to go out. I've tried opening all the windows on the second floor, but the temperature seems to still refuses to drop by much up there, probably because there is close to no wind these past few days. I was thinking that I could improve air circulation by sticking fans in the windows. My question is, if I did so, which way should I stick the fans? Would it be more effective in cooling the rooms to have the fans blowing cooler air from outside into the hot rooms, or to have the fans blowing the hot air inside the rooms out the window?

—Lowellian (reply) 07:09, 10 June 2008 (UTC)

Fan pushes air which is in front of its blades. It does not suck from behind. Window fan, or as I call it Exhaust fan may solve your problem. manya (talk) 07:33, 10 June 2008 (UTC)

I'm sorry, manya, but your explanation isn't correct. Fans generally take air from one side of the blade disk and push it out the other side of the blade disk. With regard to the original question, if the fan were mounted in a duct, so that all of the air was constrained to travel within the duct, I think you'd find that air flow would feel the same on either the inlet or outlet sides of the fan. But room fans aren't mounted within a duct so the airflow isn't so constrained. I think the cause of the effect is two-fold: air flows into the fan blades from a variety of directions and a rather large "subtended angle". Because of the large subtended angle, the inflowing air can move at a pretty low velocity and yet move into the blades a large volume of air. On the outlet side, though, the moving air stream is probably more focused, so the same volume of air needs to now move at a higher velocity. A second-order effect is that the outlet air stream probably tends to drag surrounding air along with it, decreasing the stream's velocity but further increasing its volume (in the same fashion as a jet pump moves more water). This would probably be a lot easier to explain if the Reference Desk were equipped with a wind tunnel so you could see, via the smoke streams, the various flows of air. ;-)

With regard to exhaust fans, see whole-house fan.

Atlant (talk) 12:06, 10 June 2008 (UTC)

Good answer! --Anonymous, 00:01 UTC, June 11, 2008.

The best way to clear out the air in a room is to have one window fan blowing air out, and another one across the room blowing it in. I speak from broken-air-conditioner-in-102-degree-weather experience. --Sean 12:56, 10 June 2008 (UTC)

I'm with Atlant with his explanation. To explain it slightly differently, the air being blown out of the fan is focused to travel in a specific direction by the shape of the blades, therefore the moving air takes up a given volume (lets call it x for fun). On the 'input' side of the fan, there is no such restriction on where the air comes from. As the blades push the air directly in front of them out of the way into the volume x above, there is a (momentary, instantaneous, imaginary, useful for this exercise) vacuum that is created because there is no air present. To keep the air pressure in the volume constant, the atmosphere rushes in 'uniformly' and 'from all directions'. Because its coming in from all directions, it occupies a greater volume and (as Atlant said) the flow rate is lower because theres a greater volume flowing.

To address your second concern, Sean is correct. Having all fans blowing outward would be the least useful solution because (assuming theres no other source of air) all of the air would have to travel through the rest of the (substantially warmer) house before it could reach the second floor, which would minimize cooling capacity. If all the fans face in, you'll get lots of cool air in but the warm air in the house will still be present increasing the amount of air that needs to be cooled. But having an equal number pushing in and pulling out will bring an influx of cool air (what the first method lacks) and also remove warm air (what the second method lacks). If done correctly, it will also reduce the amount of electricity needed compared to the other two. EagleFalconn (talk) 13:28, 10 June 2008 (UTC)

You don't even need the fans - just opening one window at the front of the house and one at the back (and the internal doors inbetween) will create a significant flow of air through the house. The fans will increase the effect, especially if there is no natural wind, but they aren't essential for the basic principle. --Tango (talk) 15:25, 10 June 2008 (UTC)

Here's an article I wrote on home cooling with fans: [15]. It seems to answer most of your questions listed under part 2. In your case, I recommend blowing cool air in on the lower floor and out on the second floor. Note that this will cool the lower floor more quickly than the upper floor, though, as the hot air on the lower floor must first move to the upper floor before being exhausted. You might want to sleep on the lower floor if it remains too hot upstairs. The other option is to have fans blowing in and out on both floors.

Note that the inside temp often increases after sunset because the exterior walls, which have been absorbing sunlight and changing it into heat, begin to radiate this heat inside the house. The delay between when the sunlight is absorbed and the heat reaches the inside has to do with the thickness of the walls and their thermal conductivity. Something like a 6 hour delay is typical for the average brick house. Thus, if the hottest point outside is at 3 PM, the hottest point inside may not occur until 9 PM. Hosing down the brick wall periodically may also help to reduce the heat which they contain. Be sure to close any windows, first, though. StuRat (talk) 20:52, 10 June 2008 (UTC)

I'll throw a couple more tidbits into this dicsussion, as I too lived in a house with no central AC for 25 years.

• If you only have one fan, have it exhaust the hot air.
• If there's any breeze at all, use it -- don't try to exhause hot air into the wind!
• If you have a built-in fan in the bathroom (a "fart fan"), use it too -- it's closer to the ceiling than anything else.
• Having a fan blowing on you is pseudo-cooling; you're increasing the evaporative effect but doing nothing to cool the rest of the room.

And despite all that, sometimes you just have to sleep on the floor in the basement :-). --Danh, 67.40.166.141 (talk) 23:49, 10 June 2008 (UTC)

I have to disagree on using a single fan for exhaust. That will result in a slight negative pressure in the home which may cause air to backup down chimneys, may suck in bugs and dust when you open exterior doors, etc. Also, a room in which the fan blows inward will quickly cool, and the air circulation will make it feel even cooler than it is, so that's a good place to sleep. StuRat (talk) 04:59, 11 June 2008 (UTC)

StuRat, the "single exhaust fan" is the exact working concept behind the whole-house fan. The idea, of course, is that you don't just exhaust from the house, you also open "inlet" windows , usually concentrating on the room(s) that you're currently occupying. This (and the damper that you've installed on your chimney) prevents pulling soot, bats, etc. down the chimney or radon from below the basement floor. And because the exhaust fan is usually located remotely from you, you don't hear it very much. I've lived in two houses now that had whole-house exhaust fans and found them to be very useful. Their principle disadvantage is that because you're circulating exterior air through the house, you're alos bringing in pollens and other exterior pollutants.

With regard to bathroom exhaust fans, before anyone implements that strategy, be sure you know where the exhaust from you bathroom fan goes! Some just recirculate through an activated carbon filter and those will be worse-than-useless in helping to cool you. And some that are meant to exhaust to the outside aren't properly installed. My curent house was an example of this. All our various bathroom fans exhausted into wall spaces and the previous owner's use of these fans resulted in nothing but the creation of rot. Mis-exhausted fans won't help keep you cool either.

Atlant (talk) 11:54, 11 June 2008 (UTC)

I suppose I'm biased here because we have a defective chimney with no cap or damper (which led to a friendly visit from our neighborhood squirrel doing his Santa impersonation), and the whole house smells of smoke when I have more fans blowing out than in. However, even in a home without a fireplace or with one tightly sealed, there are still exhaust vents from the water heater, furnace, and dryer (unless they are electric), so creating negative pressure in the home could cause those to back up. If they are properly functioning and enough windows are open they likely won't back up but will only work somewhat less efficiently. Another risk is that negative pressure can pull air out of the wall spaces, which might have mold spores in them, while a positive pressure would push the air in the wall spaces outside. However, as blowing air in (with windows open where you want to exhaust air) will result in just as much air exchange as blowing air out, why take the chance if you have the choice ? StuRat (talk) 14:59, 11 June 2008 (UTC)

One further point. I live in a house with an unfinished attic above the second floor. The "ceiling" of the attic is simply the underside of the roof structure, and the "floor" is the structure supporting the second-floor ceiling. The important thing is that the attic space is not thermally part of the house, but is part of the outdoors; the attic "floor", not the "ceiling", is covered with insulation. If your house is like this, it may be helpful to increase the ventilation between the attic and the outdoors by adding vents; since the attic is heated during the day by sunlight on the roof, ventilation reduces heat buildup. It may also be desirable to increase the amount of insulation, both to reduce warming of the second floor by the attic in summer and to reduce heat loss through the attic in winter. --Anonymous, 00:01 UTC, June 11, 2008.

Thanks for all the advice, everybody! Keep cool! ;) —Lowellian (reply) 05:27, 14 June 2008 (UTC)

Physics -- Force, Mass and Acceleration

I've been asked this question by somebody who found it in a book (which didn't bother to provide the answer): We know that F=ma. If we consider a constant acceleration, and then plot a graph of the force required to give/achieve that acceleration against different masses taken, the graph assumes the form of a curve. Why is it so, knowing that the relation between force and mass is linear? 117.194.226.154 (talk) 08:11, 10 June 2008 (UTC)

I'd be interested in seeing a sample of that graph, or at least the specific axes used (and anything else non-obvious, like not being simple/unconstrained linear motion, etc). As described, F vs m for some constant a should indeed be linear as you say. DMacks (talk) 08:17, 10 June 2008 (UTC)

I think the only reason it would curve is if a is being factored into the graph, and is only held constant at intervals, but not during the entire length of the graph, or else if a was always the same value it would be linear as stated.--十八 10:06, 10 June 2008 (UTC)

Yeah, it should be a straight line, unless we're missing a key detail. Of course, a line is a type of curve by the strict mathematical definition, so perhaps that's what it means... a rather strange way to say it, though. --Tango (talk) 12:48, 10 June 2008 (UTC)

Yeah, assuming a vacuum with no other forces acting on the mass, it should definitely be a straight line. Certainly in many realistic situations you would get a curve, though, due to things like air resistance or friction on the surface it's travelling on - is that perhaps what the book was referring to? ~ mazca ^talk 12:53, 10 June 2008 (UTC)

I suppose it could have a slight curve to it, because the gravity of the mass of the object to be accelerated is also attracting the mass of the observer, thus reducing the acceleration of the object away from the observer (or increasing the acceleration toward the observer). However, this effect would be beyond what could be measured, unless you were dealing with a rather massive object. StuRat (talk) 20:21, 10 June 2008 (UTC)

The question wasn't about gravity, it was about an arbitrary force. --Tango (talk) 22:42, 10 June 2008 (UTC)

The point is that if you have any two objects with mass (one being the observer and the planet, ship, etc., where they are located) there will be some gravitational attraction, which will affect acceleration of one object relative to the other, and therefore the force you must apply to achieve any desired acceleration. This has such a minor effect for objects of any reasonable mass that it can safely be ignored, but the effect would become measurable for massive objects. StuRat (talk) 04:51, 11 June 2008 (UTC)

I'm sorry, but I don't have any sample of that graph. The book didn't provide any. It only said that force was plotted on the y-axis, and mass on the x-axis. But I've been assuming that the graph was somewhat like a rectangular hyperbola. 117.194.225.216 (talk) 06:43, 11 June 2008 (UTC)

Do you have any details of the book (Title, Author, ISBN number) so we can try and find it online? SpinningSpark 06:58, 11 June 2008 (UTC)

Perhaps it has to do with the fact that as the mass approaches infinity (speed approaches lightspeed), the force required to achieve a certain amount of acceleration increases non-linearly? F=ma fails to hold at relativistic levels. Imagine Reason (talk) 14:56, 15 June 2008 (UTC)

Gyroscope

Why angular momentum is in direction of rotating axis?Shouldn't it be in the direction of spin? —Preceding unsigned comment added by 220.240.81.247 (talk) 12:40, 10 June 2008 (UTC)

The direction of spin is different on different parts of the spinning body, and at different times. Consider the hour hand on a clock, for example. At 12, the hand is moving to the right, at 3 it's moving down, at 6 it's going to the right left at 9 it's going up. The direction of the axis is the only direction which is constant (that's basically what "axis" means), so it's the only one you can usefully use in the definition of angular momentum. --Tango (talk) 12:51, 10 June 2008 (UTC)

At 6 it's going to the left. Am I allowed to just change your comment to fix minor mistakes like that? — DanielLC 14:22, 10 June 2008 (UTC)

Thanks! I've fixed it. I wouldn't mind you just correcting it, but others might - it's easiest just to reply like you did. --Tango (talk) 15:21, 10 June 2008 (UTC)

Neptune

A diamond on Earth retains a certain shape and hardness(?). What would happen to a diamond if it was placed on the planet Neptune? Will it become harder or change in any way? --Vincebosma (talk) 15:45, 10 June 2008 (UTC)

Also, what would happen if a human spaceship attempted to land on Neptune? --Vincebosma (talk) 15:45, 10 June 2008 (UTC)

This sounds like it might be a homework question, so I won't give you a complete answer. I think the first thing you need to consider is what you actually mean by "placed on" and "land on" - Neptune is a gas giant, there is no land, at least not without going deep down into the thick atmosphere. The things you'll need to consider when determining what will happen to things on Neptune are pressure and gravity. Our article on Neptune will give you some data that should help with that. --Tango (talk) 15:52, 10 June 2008 (UTC)

I guess I'm flattered you thought this was a homework question, but I am a 35 year old man with no homework. Just a curious question. So considering Neptune has no land, the question about diamonds and human spaceships won't matter. I was trying to determine what would happen to things like diamonds and human spaceships on planets (with land) that are at least 20x larger than Earth pressure-wise and gravitational-wise. --Vincebosma (talk) 15:57, 10 June 2008 (UTC)

Planets that large are almost certain to be gas giants. They will have a solid core, but it's a long way down. There will be very high temperatures and pressures, which diamonds can probably survive intact, but spacecraft wouldn't. You might find Galileo (spacecraft) interesting - it sent a probe into the atmosphere of Jupiter, which was destroyed by the harsh conditions (after sending back lots of useful data) - the article gives some details. It is possible to have spacecraft in the upper atmosphere, though, see Floating city (science fiction) for (a little) more information. --Tango (talk) 16:32, 10 June 2008 (UTC)

What you need is a phase diagram for carbon. We don't seem to have one on Wikipedia, but Google should find you several. If you know the local temperature and pressure, you can determine whether your diamond will be stable. I note that diamond is a pretty stable allotrope of carbon at high pressures and moderately high temperatures (thousands of degrees). There has been speculation in the past that the core of Jupiter may be (mostly) a large diamond, formed by the heat and high pressure. There's also suggestion that Jupiter will have layers of other rather exotic materials as well, including metallic hydrogen. TenOfAllTrades(talk) 17:19, 10 June 2008 (UTC)

According to our Neptune article, the core is several thousands of degrees hot, so a diamond could burn (if oxygen was present) or melt (but the high pressure might prevent this). StuRat (talk) 20:15, 10 June 2008 (UTC)

Hi. Well, probably due to its low density compared to earth, Neptune only has about ~2% more gravity than earth at the cloudtops (I don't remember the exact figure). Also, it has been theorised that the pressure at the cores of Uranus and Neptune can put methane under enough heat and pressure so that it forms diamonds (the CH₄ is stripped of its hydrogen, which forms metalic liquid hydrogen, then the leftover carbon is compressed into diamonds). It might be better to land on a moon of Neptune with reasonable gravity such as Triton, but it's -225C there. Depending on which layer of Neptune you are in, you may have to face temperatures anywhere from -240C to +15000C, gravity anywhere from 0.5x Earth to 220x Earth, and gasses from hydrogen to methane to ammonia. There might also be electrical storms in the planet. Hope this helps. Thanks. ~AH1^(TCU) 21:11, 10 June 2008 (UTC)

That 220g figure sounds highly suspect to me, do you have a source for that ? StuRat (talk) 04:43, 11 June 2008 (UTC)

Hi. Actually, no, I just calculated based on OR and that gravity goes up up the square of distance. Thanks. ~AH1^(TCU) 00:30, 14 June 2008 (UTC)

In that case, I'd love to see your assumptions and calculations, because I suspect there's a big mistake in there somewhere. I'm guessing you're using a point-mass model, which is highly inaccurate within a planet's atmosphere. With gas giants, at the top of the atmosphere the density is very low, so there is a great distance to any substantial mass, so the gravity is low. At the bottom of the clouds/top of the ocean, the density is much higher, but there is a great deal of mass above you pulling upwards, which cancels out much of the gravity pulling down. At the bottom of the ocean/top of the solid core, the density is even higher but the mass above is greater yet, so there still is a major effect of the pull upward working against the pull downward. There's also a great deal of mass on the sides of your location, which, of course, also cancel each other out.

Gas giants also spin at a rapid clip, reducing the gravity substantially, due to apparent centrifugal forces. Note that our Neptune article states that the "equatorial surface gravity" is only 1.14g. This NASA fact sheet confirms that info: [16]. Note that Saturn and Uranus even have less gravity than Earth. StuRat (talk) 05:05, 14 June 2008 (UTC)

Physics

Are there any scalar quantities which are formed by a product of 2 vector quantities? Can anybody give some examples of such. —Preceding unsigned comment added by 124.43.211.252 (talk) 16:19, 10 June 2008 (UTC)

Yes. See Mechanical work#Force and displacement for one example. --Tango (talk) 16:34, 10 June 2008 (UTC)

(edit conflict) Yes, there are several. It's unlikely that anyone here will answer your homework question for you, however. I'll give you a hint—force is a vector quantity. I suggest you examine the basic physics formulae that you've been taught and look for scalar and vector terms. TenOfAllTrades(talk) 16:38, 10 June 2008 (UTC)

Have you read dot product? Graeme Bartlett (talk) 06:16, 11 June 2008 (UTC)

Do your own homework, kid! 117.194.226.115 (talk) 18:11, 11 June 2008 (UTC)

Intelligence enhancing drugs

Have there been any drugs that show a positive correlation between intelligence and their use? ScienceApe (talk) 16:41, 10 June 2008 (UTC)

Have you looked at Nootropic? Friday (talk) 16:42, 10 June 2008 (UTC)

Do any of these replies help?--droptone (talk) 11:59, 11 June 2008 (UTC)

Wired Magazine actually covered this topic briefly in their May issue. Check it out here. They suggest adderal, Aniracetam, aricept, methamphetamine, modafinil nicotine, rolipram, and vasopressin may potentially "boost cognitive output," although many of these drugs have negative side effects and may also be illegal in your area. --Shaggorama (talk) 07:54, 15 June 2008 (UTC)

Looking-glass protein

Assume we found an alternate form of life identical to something we know is edible(say, an apple), except that the structure of its proteins and other molecules was opposite in chirality to that of life as we know it. If we ate such "looking-glass" food, would it be poisonous, or just pass through the body inertly? Would it even be possible for mirror-imaged proteins and molecules to form complex life similar to ourselves and what we eat? —Preceding unsigned comment added by 207.233.86.164 (talk) 17:30, 10 June 2008 (UTC)

There is no real bias within chemistry and chemical reactions for specific chiralities. That is to say that enantiomers have the same chemical properties. If we were to come across an apple that had the opposite chirality (for example, all the sugars in it were the enantiomer of dextrose) its effects would be difficult to say arbitrarily. There are certain molecules that the body would simply allow to pass right through as its different chirality would make it neigh impossible for any proteins to sucessfully catalyze the digestion. On the other hand, there are also molecules for which the change in chirality would make them horribly horribly poisonous. See thalidomide. There is no reason for biology to be biased towards R molecules, and to my knowledge research is being done to determine why that bias arose. If I recall correctly, the current theory has something to do with the strong force, which seems a little off kilter to me but I'm not really qualified to judge. (EagleFalconn) 17:46, 10 June 2008 (UTC)

The main theory I know of is that the chirality of organic molecules is purely by chance - it just happens that the first life forms to be successful were of that chirality and every life form since has therefore also been. It's an interesting issue, and has many consequences for the fundamental ideas of evolution. To the best of my knowledge, there is no reason why life couldn't form with everything the exact mirror image of what we observe. Interaction between life forms of each type (for example, us eating a mirror-apple) would be unpredictable, as you say, but interactions between molecules of one type should be indistinguishable from interactions between molecules of the other type. --Tango (talk) 17:53, 10 June 2008 (UTC)

Right, my point in the above comment was to say that there is a theory that states that R may have been favorable due to a strong force interaction, which is to say that it wasn't entirely chance but there was something driving it (perhaps competitive reaction kinetics). Interestingly, it isn't necessarily true that just because an interaction works R,R that it will work S,S. As I say above, enantiomers have the same chemical properties, however diastereomers do NOT. So just because we know what an R sugar coupling with an R protein will do, we don't know if it'll do the same thing with the S sugar and the S protein. EagleFalconn (talk) 19:38, 10 June 2008 (UTC)

That sounds off...unless there's a third chiral thing involved (external entity or noticeably affected by low-level like asymmetric Force), enantiomers are completely structurally identical and perfect 3D mirror images, so why wouldn't one think R-substrate + R-enzyme would be identical and bind identically (except perfectly enantiomerically) to S-substrate + S-enzyme? If they don't, then enantiomers aren't really "perfect mirror images". DMacks (talk) 19:48, 10 June 2008 (UTC)

I agree. Except for the possibility of very small effects with the strong or weak nuclear forces, the laws of physics are invariant with respect to taking mirror images, so the S versions of things should interact with each other in the same way the R versions do. --Tango (talk) 20:08, 10 June 2008 (UTC)

Well, but we know that diastereomers have different chemical properties (R,R != S,R != R,S != S,S) so while individually the substrate and the protein would be chemically identical to their enantiomers, wouldn't (A) the diastereomeric compound they make have different chemical and physical properties depending on whether it is R,R or S,S? And therefore, (B) Wouldn't the metabolization therefore have different requirements that the remainder of our body, having only been mirror imaged as opposed to also having metabolic processes changed (temperature, activation energy provided, catalyst (since R,R,R would, again, have different properties than S,S,S etc), would be unequipped to meet? We might say that its a small change, but biology is very sensitive to small changes because of the complexity of the systems. I'm guess I'm not really following your disagreement, do you disagree with point A or B? Also, I agree that the strong force thing is weird, I'm just repeating something I found in my organic textbook (Loudon 4th edition) that I used in my optics class. EagleFalconn (talk) 13:51, 11 June 2008 (UTC)

As long as you take the mirror image of absolutely everything, it shouldn't make any difference (except the results will all be mirrored, of course). When we say they have different chemical properties we mean in relation to everything else staying the same, if everything else is mirrored with them, the properties should be identical. Symmetry under parity inversions is a pretty fundamental law of physics. Incidentally, I think it's the weak force, not the strong force, which violates it (at least, that's what it says in that article), and the weak force governs things like radioactive decay, chemistry (and therefore biochemistry) is governed by the electromagnetic force, which is symmetric. --Tango (talk) 14:08, 11 June 2008 (UTC)

I looked up a citation, Loudon 4th Edition page 277 and 278. First part addresses enantiomers forming diastereomers (the substrate binding to the enzyme/protein):

Enantiomers have different reactivities with chiral reagents because diastereomers have different free energies. Just as diastereomers differ in their other physical properies they also differ in free energies. In this case, the transition state for the reaction of one enantiomer is the diastereomer of the transition state for the reaction of the other. Because diastereomeric transition states have different energies, the reaction of one enantiomer occurs more rapidly than the reaction of the other (Note that we may not be able to predict which enantiomer will be more reactive)

— Marc Loudon, Organic Chemistry 4th Edition, page 277

Emphasis not mine, by the way. I believe that the above guarantees that R,R would have a different reaction rate than S,S. In addition:

Disatereomers in general have different reactivities toward any reagent, whether the reagent is chiral or achiral. The reason is that, in the reactions of diastereomers, both the starting materials and the transition states are diasteromeric, and disastereomers have different free energies. Consequently, their standard free energies of activation, and hence their reaction rates, must in principle differ...We may not be able to predict which alkene is more reactive or by how much, but we can be sure that the two alkenes will not be equally reactive.

— Marc Loudon, Organic Chemistry, 4th edition, Page 288

This part indicates that the substrate, once bound to the protein, will also have different energetics. Does this sound reasonable? EagleFalconn (talk) 14:42, 11 June 2008 (UTC)

(outdent). Those quotes are exactly what we're saying and is what you're misinterpretting: it's talking about each of two enantiomers of one compound reacting with the same (one constant) enantiomer of another. See where it says diastereomeric transistion states are different? That means it's an S+S vs S+R type of comparison, not S+S vs R+R (which would be enantiomeric). So it's talking about how a "normal" enzyme reacts with its natural-sugar substrate vs with the enantiomer of that sugar, not how the enantiomer of the enzyme reacts with the enantiomer of the sugar. Or how the (enantiomeric) product of the (enantiomeric enzyme + enantiomeric sugar) would react with the rest of biology in a "normal" (non-enantiomeric-world) system. Consider hands and gloves: left hand fits into left glove identically to how right hand fits into right glove. But left vs right hand fit differently into left glove. And (left hand in left glove) shakes hands with someone else's left hand identically to how a (right hand in right glove) shakes hands with someone else's right hand, but (left hand in left glove) shakes differently with someone else's left hand vs right hand. DMacks (talk) 16:06, 11 June 2008 (UTC)

Point conceeded, thanks. The point that I was missing was that S+S is the enantiomer of R+R. EagleFalconn (talk) 16:23, 11 June 2008 (UTC)

Regarding specifically proteins and amino acids, and the effect of eating an apples with opposite chirality proteins: I'm pretty sure that the D-isomers of amino acids have greatly reduced bioavailability. This comes up because some chemical treatments that foodstuff might be subjected to, such as strong alkali, tend to racemize amino acids. ike9898 (talk) 19:52, 10 June 2008 (UTC)

Increased Gravitational Pull on Earth

What exactly will happen if the gravitational pull on Earth increased ever so slightly? Such as, will I weigh heavier, will certain animal or plant species suffer and die off, etc. --Vincebosma (talk) 19:43, 10 June 2008 (UTC)

That depends on what you mean by "ever so slightly". The Earth's gravity already varies by very small amounts depending on where you are (by about 0.5% or so), and that clearly doesn't have any major effects. It needs to be taken into account for some satellites, I believe, so changing the strength of gravity by less than a percent would probably mess up GPS, but that's about it. Everything would weigh more, but not enough to cause any significant effects. If you increase gravity enough, though, things would start to be unable to support their own weight and would collapse. How much you would need to increase it by depends on what you want to collapse, I don't have any example figures for you, though. I expect it would increase air pressure, although it may in fact decrease it above a certain altitude (the scale height would decrease). I'm not sure what effects that might have, but it could well affect the climate. It would cause the moon to move closer, shortening the length of a lunar month and increasing tidal forces. There are probably all kinds of other effects I haven't thought of, as well. How significant each of them will be depends on how much you increase gravity. --Tango (talk) 20:05, 10 June 2008 (UTC)

How about as a reference, instead of weighing 200 lbs, due to the increase, I weigh 250 lbs.....--Vincebosma (talk) 20:09, 10 June 2008 (UTC)

Among other things, the moon's orbit will destabilize causing it to impact Earth. Everything else is pretty minor at that point. (Assumes 25% more gravity w/ no other physical changes) — Lomn 20:31, 10 June 2008 (UTC)

A 25% increase in gravity would cause the moon to impact the Earth? I'll have to find the back of an envelope, but that sounds unlikely... Do you have the numbers for that, or are you just guessing? --Tango (talk) 21:51, 10 June 2008 (UTC)

According to the back of my envelope, a 25% increase in Earth's gravity would cause the Moon's closest approach to each to be about 2/3 of what it is now, that's nowhere near enough to hit the atmosphere and impact Earth. (Note, there are very rough numbers - I'll try a more accurate calculation in a sec.) --Tango (talk) 22:02, 10 June 2008 (UTC)

(The more accurate calculation is proving more complicated that it's worth, the 2/3 figure should be pretty close, and it's far far outside the atmosphere, so there's plenty of margin for error. --Tango (talk) 22:11, 10 June 2008 (UTC))

You're right, my back of the envelope was way off. — Lomn 23:27, 10 June 2008 (UTC)

But would that closer approach allow the Moon to much more efficiently strip off the atmosphere? That could have a somewhat negative impact. (takes a deep breath) Franamax (talk) 16:44, 11 June 2008 (UTC)

Clarify that - the moon is not in the atmosphere per se, but it is now sweeping out a zone with a higher density of gas molecules (I mailed my envelope with the water bill, no idea how much higher). Wouldn't moving the swept zone closer to the breathable part of the atmosphere increase the outward diffusion? Or not? Franamax (talk) 16:53, 11 June 2008 (UTC)

According to exosphere, the atmosphere ends at about 10,000km above the surface of the Earth, although I'm not sure how that's defined, seems pretty arbitrary to me. That's 16,000km above the centre of the Earth. At 2/3 it's current distance, the Moon would be about 270,000km away. That's a whole order of magnitude bigger, I think we can safely ignore all atmospheric effects. --Tango (talk) 17:42, 11 June 2008 (UTC)

You might have quite a number of buildings and bridges in the world collapse. Although many structures were built with tolerances that could handle a 25% increase in constant load, many others weren't. Those structures that are already near their maximum safe load would collapse. The nearer moon and increased gravitation would affect the tides, which could affect certain parts of the ecosystem. All creatures would have to develop stronger muscles to support their bodies, and the hearts would have to work overtime, leading to shorter lifespans for most creatures above the size of a large insect. The jumps made by skateboarders, skiers, etc. wouldn't look as impressive as they do now. Actually, just about anything you stop to consider would be affected in some way. 152.16.16.75 (talk) 10:22, 16 June 2008 (UTC)

Jumping from big heights

I have recently seen the Bourne Ultimatum (great film by the way) and was a bit confused by the ending. Bourne supposedly jumps from a ten, I think, storey building into a river and survives. This doesn't strike me as terribly realistic and I'm sure I wouldn't be quite as successful if I tried it. Is this Hollywood bending the laws of reality for its own needs again or is there some military training that can prepare you for jumps like that? Is it actually be possible? Thanks. 92.0.243.212 (talk) 20:16, 10 June 2008 (UTC)

Outside Magazine says "The highest Olympic-level dive distance is ten meters (33 feet), with good reason. Beware of injury at around 15 to 20 feet and know what you're doing above 30 feet. Anything over 50 is pro territory." The Discovery Channel explains "Perhaps the biggest misconception about cliff diving is that the diver is cushioned by the water below—this could not be further from the truth. When leaping from a cliff that is over 70 feet high, a diver hits the water at over 46 mph, regardless of his or her body weight." (70 feet is 21 metres) I do not know the answer to the training part of the question. WikiJedits (talk) 20:51, 10 June 2008 (UTC)

At the very least, you would expect him to break his legs on impact (did he at least land feet first? Diving head first from that height would almost certainly kill you!). Other than landing feet first, so your legs take the impact, not your head, I can't see anything you could be trained to do that would help. There is an urban legend about throwing something ahead of you to break the surface of the water so it won't be so hard when you hit it, but as far as I know, that's complete nonsense. --Tango (talk) 21:50, 10 June 2008 (UTC)

Kinda funny you should say that as, if you haven't seen all the Bourne films, in the first one he falls what looks like at least 10m from the top of a stairwell but survives because he was good enough to push some else over first and land on them. But again, could just be Hollywood's attempt at the wow-factor. 92.0.243.212 (talk) 20:29, 11 June 2008 (UTC)

You could be trained to execute a parachutist's landing where you hit with feet, then thigh, hip, shoulder, to spread the energy out. Also, according to one of those "Worst-Case Scenario" books, you should clench your buttocks so that a jet of water doesn't tear a hole in your colon. --Sean 22:50, 10 June 2008 (UTC)

The Golden Gate Bridge at 750 feet (220 m) is a popular spot for suicidal jumpers. Despite the extreme height, relatively cold water (50-60 F / 10-15 C), and frequent strong currents, about 2% of jumpers nonetheless survive. So it is certainly possible. A person like Bourne in peak physical health who presumably knows how to enter the water in a controlled way might well have a decent shot of executing a 100 ft dive, though it certainly wouldn't be easy or a sure thing that he would survive. So I'd say it is certainly possible, though I wouldn't recommend it. Dragons flight (talk) 22:07, 10 June 2008 (UTC)

See La Quebrada Cliff Divers, which daily dive off 45m cliffs - this is more than most 10 storey buildings. I assume that they survive ;-). I have dived 10m. If you enter the water optimally (for me that is vertical, feet first, as I'm a craven coward rational person), there is very little impact stress. If you are more than a little off, you get quite a kick. I don't want to experience what happens if you enter the water uncontrolled... --Stephan Schulz (talk) 22:24, 10 June 2008 (UTC)

I'm not going to give this a try but by 'optimally' what do you mean? A pencil dive, feet first? Would your body be tense, to keep you in that pencil shape, or relaxed, so that you don't break your bones on impact? 92.0.243.212 (talk) 20:33, 11 June 2008 (UTC)

Interesting. Seems you can do it, if you know what you're doing. Shows what I know! --Tango (talk) 22:40, 10 June 2008 (UTC)

This is a bit off topic, but I seem to recall that the water in at least some diving events is aerated. Is this primarily to give the diver a visual reference, or is it intended to provide a degree of cushion on entry? -- Tcncv (talk) 01:14, 11 June 2008 (UTC)

I don't know if the aeration actually exists, but if it did it would lower the surface tension of the water and lessen the impact force. However, the same amount of work would still need to be done to stop you, and so you'd need a deeper pool to do it.EagleFalconn (talk) 13:55, 11 June 2008 (UTC)

I know they have a small spray hitting the surface to make it easier to see where it is (so you know when to stop somersaulting, or whatever). I don't think it has any affect on the landing, though. I'm not sure how significant surface tension is to the impact force, I think it's just the fact that liquids are incompressible that makes them seem so solid (the water can't compress like a crash mat, it has to move out of the way, and that takes time). --Tango (talk) 14:00, 11 June 2008 (UTC)

I'd suspect that the small spray is just to be able to tell where the surface is. To my knowledge and experience, surface tension and viscosity are coupled effects which are the impact force, as they directly relate to the incompressibility of the liquid. EagleFalconn (talk) 15:57, 12 June 2008 (UTC)

Just to correct a misconception: the surface tension is negligible. The relevant dimensionless number is the Weber number which in this case works out to be about 10 million. Given that surface tension effects are only important if We is less than or approximately equal to one, we may safely ignore surface tension. Robinh (talk) 13:17, 13 June 2008 (UTC)

(edit conflict):

1. Surface tension is one of the variables in the Weber equation, so it is clearly not negligible
2. I've never seen this before, but it looks like it's about fluids in motion so it probably isn't that useful in describing swimming pools.

Feel free to correct me if i misunderstood something here. --Shaggorama (talk) 07:38, 15 June 2008 (UTC)

Robinh is correct. The Weber number calculation says that forces from surface tension are a factor of 10 million smaller than forces from inertia. That's negligible. The velocity in question is the relative velocity of the body (i.e. the diver) normal to the fluid interface (i.e. hitting the water). JohnAspinall (talk) 20:41, 16 June 2008 (UTC)

Cat spray / Territorial marking

This question relates to a "cat pee" question posted by another user above. I'm convinced that the stuff that cats "spray" when marking their territory isn't urine. From having to clean it up, I know that it is oily and extremely musky. I assumed it was some sort of gland secrection, but our articles on cat and territorial marking refer to this stuff as urine. Can anyone clarify whether or not it is urine? ike9898 (talk) 20:18, 10 June 2008 (UTC)

I believe it is urine, but does include certain gland secretions which give it the distinctive smell (well, distinctive to cats - just smelly to us!) --Tango (talk) 21:45, 10 June 2008 (UTC)

It is urine plus anal gland secretions. According to this paper the secretions contain volatile fatty acids (which might constitute the greasy feel), putrescine, cadaverine, and ammonia(which contributes to the unholy smell). The secretion-urine mix also contain lipids and dead cells.--Lenticel ^(talk) 22:48, 10 June 2008 (UTC)

. . .another cup of tea anybody?! Richard Avery (talk) 06:47, 11 June 2008 (UTC)

ball lightning?

Hi. This morning there was a big thunderstorm where I live (southern Ontario). A friend told me he heard ball lightning. He reported the following:

• Two seconds of hissing, then a loud thunderclap
• It sounded like a Roman Candle (firework)
• The lights went dim noticeably for about 10 minutes, occasionally flickering, then suddenly went back to full power
• He had read a book containing information about ball lightning before the thunderstorm
• Location: less than 500 m from where I was at the time, was indoors

The thunderstorm:

• Can be classified as severe, but no warning was issued
• Lightning every several seconds
• Rainfall rate showing up as dark-red on The Weather Network radar
• Was located near a cold front
• Occured before 8 am EDT, did not weaken overnight
• Was located near central-eastern USA the night before, preceded by a few severe and non-severe thunderstorms in S. Ontario the afternoon and night before
• Severe thunderstorms lasted roughly 15 mins, entire storm roughly 25 mins, rain roughly 30 mins

I noticed:

• Frequent and bright lightning, sometimes within 1 km
• Thunder loud enough to wake me up
• Strong winds and gusts, ~80 km/h
• No noticible disruptions in electricity
• Widespread puddling of rain
• Enough rain to cause a mess indoors if the window is open
• Wind carrying still-falling rain nearing the ground producing waves

So, is it plausible that ball lightning really occured, and are these conditions condusive to ball lightning formation, or are there other plausible explainations? Thanks. ~AH1^(TCU) 20:54, 10 June 2008 (UTC)

God how I miss living in Southern Ontario, in the countryside, and watching those biggg storms come through. Torrential rain, blasting wind, hail - we only get polie thunder where I am now, you're lucky! Franamax (talk) 16:59, 11 June 2008 (UTC)

Without having seen the actual ball lightning, I don't think there's a lot that can be said. We don't know enough about ball lightning to know what conditions are conducive to it; in fact, we barely know that it even exists. Sure, it's plausible. And I'm sure there are other plausible explanations. The only weird part of what your friend describes is the hissing sound. I'm thinking maybe it was a transformer exploding. I don't specifically remember hissing sounds before transformer explosions I've heard, but it sort of rings a bell. Plus that would explain the localized disruption in electrical service. --Allen (talk) 21:21, 10 June 2008 (UTC)

If he didn't see ball lightning, why assume it was ball lightning? Hissing could be electrical arcing followed by the bang of a high voltage fuse fuse opening to clear the fault. Ten minutes later a utility troubleman could have replaced the fuse or closed a normally open switch to restore power. Scientists are somewhat skeptical about ball lightning. I would expect it is some sort of plasma of heated and electrically charged gas. Edison (talk) 00:00, 11 June 2008 (UTC)

Heard but didn't see is somewhat unreliable. I concur that the hearing was likely from the hydro system. In a similar storm in a similar location, I heard a serious ka-boom accompanied by a very clear sizzling sound (which you could also describe as hissing), out towards the road. The next day I had to call in for $400 worth of repairs to the control unit of my Miele washing machine. Draw your own conclusions. Franamax (talk) 17:07, 11 June 2008 (UTC)

I think the answers above are on the right track; a more mundane electrical problem is always going to be more likely than a rare one - that's just stating the obvious. That being said, I have heard some claims that ball lightning may make a hissing sound. I also enjoyed the lightshow; the wife and I stayed up until 1 AM Tuesday morning to watch the lightning and we noted that the storm was odd in a couple of ways - extreme variations in rainfall (brief bursts of intense downpours, then long intervals with no rain), a great deal of lightning - only a small portion of which was accompanied by significant thunder, even when the flashes were relatively close, and a kind of pseudo-eye where the updraft of the cell had presumably created a large indentation. I wouldn't be at all surprised to learn that weird electrical phenomena had been seen during the storm; I was quite surprised there weren't any tornadoes (at least confirmed, so far as I know). Matt Deres (talk) 13:58, 12 June 2008 (UTC)

Hi. However, he says he has experienced transformer explosions before, and the lights went fully out but that was in a different country so explosions here might be different. Thanks. ~AH1^(TCU) 21:08, 16 June 2008 (UTC)

About mirrors, and short sightedness

So I'm short sighted. Let's take this scenario: I am looking into a mirror which is six feet away. There is an object behind me which is 60 feet away. Ordinarily, I'd not be able to focus on this object very well, but I'm seeing this object behind me in the mirror. So there are two questions:

1. Will I be able to focus on the object? Am I focusing six feet away, or seventy-two feet (distance to mirror + distance from mirror to object) away?
2. Why?

Apply this scenario to an SLR camera and you'll see why I'm asking. Thanks guys. :D Lewis Collard! (lol, internet) 21:25, 10 June 2008 (UTC)

No, I don't think you would. You're trying to focus seventy two feet away, because that's how far the light has to travel. You can focus on the mirror itself, if you want; then you'll see clearly the dust and lint on it, but not the distant objects it reflects. --Allen (talk) 21:31, 10 June 2008 (UTC)

Whoah. Lewis Collard! (lol, internet) 21:36, 10 June 2008 (UTC)

I agree, you need to focus 72 feet away. I'm not sure what an SLR camera has to do with it - a camera contains a lens which focuses the light, rather than a plane mirror which just reflects it. --Tango (talk) 21:42, 10 June 2008 (UTC)

And what if I took the lens off? (I'd do this right now, but it's dark here...) Lewis Collard! (lol, internet) 21:49, 10 June 2008 (UTC)

Well, actually there's more than one lens, so it would depend on which one you removed. Single-lens reflex camera has a nice diagram showing them all. --Tango (talk) 22:26, 10 June 2008 (UTC)

Let me try a slightly more helpful answer: If you remove all the lenses (which is probably what you mean), the light would not be focused and you would get just a small amount of random light hitting the film/sensor and you wouldn't get a proper image forming. --Tango (talk) 22:37, 10 June 2008 (UTC)

As someone who owns an SLR, I tried exactly that. The result when I looked through the viewfinder: a uniform light-colored field. The result of taking a picture: a uniform 15% grey image. --Carnildo (talk) 23:49, 10 June 2008 (UTC)

Sounds about right. What were you pointing it at, and with how much light? --Tango (talk) 00:11, 11 June 2008 (UTC)

My living room, lit by indirect sunlight. Not much color or brightness variation. --Carnildo (talk) 21:39, 11 June 2008 (UTC)

In an SLR camera, there's a translucent "focusing screen" between your eye and the mirror. This screen is similar to a piece of frosted glass. The lens forms an image on the focusing screen, which you can see. But since the focusing screen is translucent, not transparent, you can't just look through the viewfinder and see through the camera without a lens to form an image—just as you can't look through the frosted glass on your boss's office door. (As a side note, when a lens is mounted and you see an image in the viewfinder, your eye is focusing on the image that's formed on the focusing screen. But that's only a couple of centimeters from your eye, which is closer than you can usually focus. This is possible because the viewfinder has a little lens, similar to reading glasses, that make the focusing screen "look like" it's far enough away to focus on, typically about 1 meter. Some cameras have an adjustment to this apparent distance, to accommodate different people's vision. Look up "diopter adjustment" in your manual.) -- Coneslayer (talk) 18:12, 11 June 2008 (UTC)

Thanks, guys, my question has been answered. Lewis Collard! (lol, internet) 22:48, 13 June 2008 (UTC)

Photosystems and Primary electron acceptors

Hello, in high school biology, my master teacher taught me that in photosynthesis, light photons hit the photosystems I and II and causes them to pass their electrons to the primary proton acceptor. The primary proton acceptor then passes them to plastiquinon to go to the cytochrome complex. My question is, where is the primary proton acceptor in relation to the PS? http://en.wikipedia.org/wiki/Image:Thylakoid_membrane.png according to this diagram, is the primary acceptor INSIDE/PART OF the PS? Applefungus (talk) 22:06, 10 June 2008 (UTC)

Toenails

Why do we still have toenails? Are they just left over from our evoloutinary ancestors? But in that case do chimpanzees need to toenails? (im not even sure if they do!) Or do they actually serve some purpose? Thankyou x —Preceding unsigned comment added by 217.44.210.227 (talk) 22:22, 10 June 2008 (UTC)

Why do we still have an appendix? ;) Just because they are no longer functional does not mean they will automatically be lost. That's not quite how evolution works. Regards, CycloneNimrod ^talk?_contribs? 22:25, 10 June 2008 (UTC)

People can actually die from ingrown toenails, which cause infection (my grandpa died that way, with diabetes, age, and nursing home neglect contibuting to it getting out of control). So, there may be some evolutionary pressure to lose them, if they no longer serve any purpose. StuRat (talk) 22:48, 10 June 2008 (UTC)

Perhaps, but remember that evolution isn't a conscious entity, it doesn't solve every problem a species has. Just because toenails can be a danger, this doesn't mean that a specific mutation is going to happen in which toenails don't grow and which will pass down to the next generation. Also there is a big debate about whether or not humans can still evolve in that way, considering how we now, for the most part, treat everyone equally regardless of disease. Increasing medical capabilities also make it less likely. Regards, CycloneNimrod ^talk?_contribs? 22:51, 10 June 2008 (UTC)

Objects slipping from your hands and objects protruding from the ground are two reasons why toenails serve some function. They might not be the most effective protections if you bang your foot against a root or rock but they did served a purpose in our savanna dwelling ancestor and still do for the barefoot aficionados of today. That they might be disappearing would be an interesting study subject. 200.127.59.151 (talk) 23:12, 10 June 2008 (UTC)

There's actually a new hypothesis out about the appendix. --Allen (talk) 00:52, 11 June 2008 (UTC)

That they are small or not is genetic. They actually do function to protect and add sensitivity to the tips[17]. Like fingernails, they protect the sensitive nerve endings on the tips of our toes and fingers. Rather than see them as clawing tools, see them as little shields. And you might like this from Nail Anatomy[18] (it's a download document) about function and purpose:

There is also an important role in offence and defence. Proprioception is gained from pressure of the pulp against the hard underside of the semi-rigid nail plate. The nail plates give form and shape to the pulp of the digit and, by attachment to the distal phalanx control and stabilise the pulp. On the foot, the toe nail is most importantly functional in its proprioceptive role, its defence of the digit and in control of the toe pulp.

Julia Rossi (talk) 00:55, 11 June 2008 (UTC)

And note that just because you can die from something doesn't make it much of an evolutionary pressure. As your very example points out, your grandfather's toenails had no effect on his ability to reproduce, only being a problem late in life and when complicated by other late-in-life illnesses. I doubt they are disappearing—they seem like a pretty basic part of primate anatomy, and without any pressure against them, they're not going to be going anywhere fast. --98.217.8.46 (talk) 00:56, 11 June 2008 (UTC)

Yes, but younger people can die from them, too, especially if they have diabetes and ignore the problem. I suffered from infected ingrown toenails myself. If I hadn't lanced to abcess and treated the area with hydrogen peroxide I might not be here now. (If you are eating while reading this, you can thank me for helping you with your diet.) :-) StuRat (talk) 04:39, 11 June 2008 (UTC)

As you leap up and run to correct your diet, you can thank toenails for giving information to the brain[19] through the pressure incurred that helps keep you upright in your flight and when walking gingerly back to your seat. StuRat this may be the document for you! Julia Rossi (talk) 05:44, 11 June 2008 (UTC)

That doc lists one of the uses of toenails as "assisting in oral maintenance" ... wouldn't that result in picking the seeds from this morning's preserves out of one's teeth only to replace them with toe jam ? :-) StuRat (talk) 06:30, 11 June 2008 (UTC)

Well if you have diabetes, I think you have more serious problems then toe nails. I would venture to guess the evolutionary pressure would be on something else, perhaps what causes diabetes in the first place not on your toe nails. As for the more general problem of ingrown nails, I don't think it would have been a big problem until recently since the biggest causes, are problem ill fitting shoes and poor nail maitence. I don't think shoes until say the past few thousands years were likely to be very tightly fitting and I doubt people cut their nails much at all Nil Einne (talk) 10:32, 11 June 2008 (UTC)

Actually, damage to the feet is one of the main risks for diabetics. I don't know the reasons, but I'm sure Wikipedia has an article on it (try diabetes!). Of course, that's one of the main risks for diabetics today, we've only recently learnt how to manage the condition, so diabetics even just 100 (or maybe even 50) years ago would probably have died long before their feet started having problems, and you can't get much evolution in 4 or 5 generations (except in exceptional circumstances is that tautologous?!). --Tango (talk) 13:25, 11 June 2008 (UTC)

The problem with diabetics and foot injuries is that they have restricted blood flow to their feet, which means that injuries do not heal, since the white blood cells needed to fight infection don't arrive. Thus, even a minor injury to the feet (like an ingrown toenail) can present a high risk to a diabetic. StuRat (talk) 14:31, 11 June 2008 (UTC)

Wierd Subconscious Dream

I have had this on my mind for a very long time. Sometimes, when Im in bed, I experience a sense that my room is a lot more spacious than it actually is, and I am really small compared to my surroundings. I can usually "feel" as if I was aware of all the walls, the format of my room. I am usually not very tired when this happens, and Im wide awake. Also, in conjunction with this, I get a feeling or subconscious image of a small circle rolling tensely on an extremely perfectly smooth surface. Usually, the surface suddenly breaks in this seemingly endless continuity of smoothness, and it starts to get extremely bumpy, and the ball doesnt roll smoothly. This gives me a very desperate and anxious feeling. This "image", however, is purely 1 dimensional, and it is usually in a grey color. When the surface the ball is rolling on becomes chaotically uneven and incontinuous, I get a really anxious, uneasy, desperate feeling. I am pretty sure all of this is subconscious, however it is not a dream, because none of this could happen in real life, like a dream. The image and consequent feeling I get is like a television screen, I mean thats what I see. I want all of you to know I dont suffer from any kind of mental disorder I know of, maybe just a bit of stress. If anyone can identify what this is and its name, it would be greatly appreciated. —Preceding unsigned comment added by 189.4.19.134 (talk) 22:42, 10 June 2008 (UTC)

Sounds like astral projection, if you're willing to believe in it. There's little scientific evidence (if any) for it, though. Regards, CycloneNimrod ^talk?_contribs? 22:49, 10 June 2008 (UTC)

Actually, now I think about it, it's probably more related to some form of lucid dreaming. These can be exceptionally strange and are more believable scientifically (although there is still very little research for it) Regards, CycloneNimrod ^talk?_contribs? 22:53, 10 June 2008 (UTC)

That's gnarly. I actually get a similar perception of expansion sometimes as I'm going to sleep as well. When it happens, it's when I'm "half-awake," not quite asleep but certainly on my way to unconciousness, not entirely unaware of my surroundings but also very much inside myself. Unlike your experience, I don't feel as though the whole room is expanding so much as the inside of my head. it's hard to articulate my experience. If there isn't a word for this sort of thing, there should be, but don't think it's that unusual. Your brain does some funny stuff as you drift off to sleep and it's probably a little different for everyone. Also, just thought i'd point out: something isn't "subconscious" if you are actively conscious of it (you perceive it). --Shaggorama (talk) 08:03, 15 June 2008 (UTC)

June 11

Does MOND have problems with Newton's third law of motion?

I read carefully the MOND article in Wikipedia, and it seems to me that it would be difficult to reconcile the idea with conservation of momentum, or at least that only some $\mu (x)$ functions would be consistent (and I cannot figure out which).

Consider an isolated star with a single planet like Pluto, small, distant, and in an elliptical orbit. As I understand MOND, the planet will always be in a gravitational field such that $\mu (x)$=1, while the star will be in a field that will be close to $\mu (x)$=1 when the planet is at perehelion, but far from $\mu (x)$=1 at aphelion. Thus at perehelion, the change in momentum of the star will balance that of the planet, but at aphelion, the momentum change in the star will be significantly greater.

This will cause the combined system to accelerate slowly but continually in the direction from the star to the planet at aphelion. This acceleration will continue until the system enters the gravitaional field of a galaxy.

I suppose MOND enthusiasts could even argue that this provides a new mechanism for the growth of galaxies, but the whole thing strikes me as counter-intuitive.

Have I understood this correctly? John Blackwell (talk) 01:42, 11 June 2008 (UTC)

According to Bekensteins paper, Millgrom's original formulation of MOND does indeed have a problem with conservation laws and some other problems as well. However, Bekenstein goes on to give a Lagrangian/Relativistic formulation that does not (he claims) have these problems. Follow the link in the references section of the article to read more. SpinningSpark 07:19, 11 June 2008 (UTC)

Thanks - I guess I'm back where I am with many things - the accurate theories are beyond my understanding (or perhaps I'm just too lazy to put in the work to understand them) - but I can't see past the flaws in the simplified descriptions. —Preceding unsigned comment added by Johnblackwell (talk • contribs) 01:21, 12 June 2008 (UTC)

Beavers

I'm trying to find out how long it takes a beaver to fell a tree like an Aspen. The photo with the article refers to cutting a 10 inch tree overnight. I would like to know if there is any more specific information on the time, assuming that 10" overnight would be 10" in 8 hrs? or 10 hrs? or 12 hrs? —Preceding unsigned comment added by 65.255.187.5 (talk) 02:03, 11 June 2008 (UTC)

I remember seeing a very good nature documentary film on beavers; I think it was by Rein Maran, an Estonian cinematographer, if my memory serves me well (it was some 20 years ago...). If you can find that documentary, you will have the answer to your question. If you find this film on the web, please give a link. All the best, --Dr Dima (talk) 06:08, 11 June 2008 (UTC)

A quick google search finds a cached article [20] saying 6" in 15 minutes. Scaling that to 10" is three times longer, although the more mature tree would also have more hard wood. Don't know if that helps... Franamax (talk) 15:18, 11 June 2008 (UTC)

I believe the time needed scales with the cube of diameter, not the square, so it would take about six times as long. In order to fell a tree, a beaver chews a wedge-shaped ring, not a cylindrical ring, so the amount of material removed increases as the cube of the diameter. Also, you need to take into account non-linear factors such as fatigue. --Carnildo (talk) 21:45, 11 June 2008 (UTC)

Yes, it is the cube. Just for fun, I tried working out the formula for the volume. for a 90° wedge, chewing 3/4 of the diameter, I get .344D³. I can do that geometrically right, I don't need an integral? My math is a little rusty :) Franamax (talk) 01:38, 12 June 2008 (UTC)

Phthalate

Though controversial, phthalates are still being used in a variety of household applications (shower curtains, adhesives, perfume), modern pop-culture electronics and medical applications such as catheters. Notable recent examples include Apple Inc.'s iPhone and iPod, and personal computers. The company has been criticized by environmental supporters claiming that tests on a commercially-purchased iPhone returned "toxic" levels of the chemical, prompting public declarations for change due to its associated hazards.

— ., http://en.wikipedia.org/wiki/Phthalate

Are iPod nanos included?21:49, 6 June 2008 (UTC)68.148.164.166 (talk)

Wow, ophthalmology (and its few derivatives) isn't the only english word with a "phth" in it? – b_jonas 10:17, 9 June 2008 (UTC)

What difference would it make? That is, what possible path is there by which a (hypothetically) phthalate-loaded iPod could poison you?

Atlant (talk) 12:20, 10 June 2008 (UTC)

I'm concerned about phthalate's estrogenic effects.68.148.164.166 (talk) 03:22, 11 June 2008 (UTC)

Unless you grind up your iPod and sniffed all the powder the amount of phthalate exposure from your iPod is negligible, and if you did sniff the powder your biggest concern wouldn't be phthalates either. --antilived^{T | C | G} 04:14, 11 June 2008 (UTC)

The problem are plastics which are in contact with fat rich food. The people who suffer most are the people needing dialysis, because for a long time the tubing and the memranes in the dialysis machine contained high amount of phtalates doi:10.1002/1097-0274(200101)39:1<100::AID-AJIM10>3.0.CO;2-Q, but for the rest a phthalate rich iphone has no chance to poison you, because the skin is not very permeable.--Stone (talk) 07:23, 11 June 2008 (UTC)

What if you alternately fiddled with your iPod and ate potato crisps/chips all day every day? From my observations some people do exactly that. Some phthalate would dissolve in the fat. You might have to worry more about the oestrogenic/estrogenic effects of the soy/soya oil the chips/crisps were fried in though. Itsmejudith (talk) 11:39, 11 June 2008 (UTC)

Phthalates are of most concern in the developmental stages, so don't let your baby play with your iPod... Franamax (talk) 17:22, 11 June 2008 (UTC)

So how do you dispose of your old iPod without putting phthalates into the environment? —Pengo 20:57, 14 June 2008 (UTC)

custom parts

does any one know a site where i can order custom metal parts? like say i wanted all the parts of a car engine...but i wanted them one third the size,where could i get that for cheap? —Preceding unsigned comment added by 76.14.124.175 (talk) 07:06, 11 June 2008 (UTC)

Hmm, not really a science question, but it might help to get an answer if you said what country you were in. SpinningSpark 07:24, 11 June 2008 (UTC)

One magazine I receive includes ads from custom metal fabricators, who can mill or make castings based on electronic CAD (machine drawing) files you email them, with quick turnaround. But unfortunately you said "cheap," which it certainly will not be. Wait a few years and "fabbers" may become as common as computer printers and scanners, and you can create your own miniature car engine via Desktop manufacturing. Edison (talk) 20:51, 11 June 2008 (UTC)

Fabbers usually work with low-melting-point materials, and occasionally with sintered metal powders. Neither is very good for making a car engine, which requires high temperature resistance and decent mechanical strength. --Carnildo (talk) 21:48, 11 June 2008 (UTC)

Opening Boxes of Tablets

There are 2 ends to my boxes of tablets (hayfever, paracetemol, aspirin, whatever). If I open it at one end I can get straight to the tray of tablets. If I open it at the other I have paper folded over the tray which contains warnings/instructions. I never look which end i'm opening so sometimes it will be (if you have the front facing you) the left-side and sometimes the right. Why is it that a good 80% of the time I get the paper-end? I would expect it to be 50/50 (2 ends, 1 end is 'clear' the other isn't) but I virtually always open it what is (to me) the 'wrong' end. I've asked a few other people and they find the same thing.

My guess is that it is down to the additional weight from the folded-paper, but wondered if A) do other people experience this too? and B) Does anybody know 'why' this might be? 194.221.133.226 (talk) 08:19, 11 June 2008 (UTC)

Here's two explanations:

1. The way the box is designed. The manufacturer wants you to look at the warnings, if only to avoid a lawsuit. Therefore, they may design the box so that it subconsciously encourages you to open it at the end with the paper.
2. It really is more like 50-50, you just don't notice it. Have you been keeping a log somehow? If not, there's a good chance that the percentage of the time you open it on the paper end is lower than you think, but you only notice a "pattern" when you open it on that end.

Or maybe you're just psychic. =) « Aaron Rotenberg « Talk « 08:42, 11 June 2008 (UTC)

I've not kept a log so it could well be that my brain is finding a pattern - i'll start a log (yeah i'm that kind of person) and see. The idea of the design sounds interesting though, I used to read a great blog that was called 'architecture of control' or something (it looked for designs that pushed people to do stuff/had a second purpose that people might not realise was actively intended). —Preceding unsigned comment added by 194.221.133.226 (talk) 09:36, 11 June 2008 (UTC)

This is related to the phenomenon I've observed whereby if a microwave oven has a turntable, and you follow the advice I've given elsewehere and set the food "off-center" on the turntable, when the cooking cycle is done, the turntable always ceases rotation with the food located at the back of the microwave oven. Seriously, I'd also suggest that the weight of the package insert instructions may be cueing you to more-often hold the box one way rather than the other. But I have no explanation for the microwave oven phenomenon except that maybe the peculiarities of the timer and turntable drive motor lead to the turntable always turning n.5 rotations (for those cooking-time values that I routinely use).

Atlant (talk) 11:41, 11 June 2008 (UTC)

How are you orienting the package? Main label side up, text reading left-to-right? That would be your first clue to unconscious positioning. There is also the possibility of the observer preferentially registering adverse events. On an unrelated note, I recall reading about a study which showed the probability that if you dropped your toast, it would land upside-down. so weird things do sometimes happen. Franamax (talk) 17:39, 11 June 2008 (UTC)

Franamax - the toast thing is to do with the average height of work-surfaces/table-tops and only having enough time for it to rotate from butter-side-up to butter-side-down (or at least that's the explanation i've been given and it sounds plausible). ny156uk (talk) 17:47, 11 June 2008 (UTC)

I'm just hazarding a possible guess here....are you right-handed (i.e. do you open the right-hand flap of the box most of the time)? Do you most of the time hold the box upright with text reading left-to-right and the flaps at either side? Zunaid©® 14:56, 13 June 2008 (UTC)

Neutrino oscillation and conservation

Suppose I measure that an electron is an electron neutrino at a given time, and I also measure that it has a certain velocity (subject of course to uncertainty). Now assume that later I measure that it's oscillated into a tau neutrino, with a different velocity. How does this work with conservation of mass/energy and conservation of momentum? I mean, you can make the velocity uncertainty arbitrarily small in both cases, so I don't see how the observer effect could account for this. Veinor ^{(talk to me)} 08:57, 11 June 2008 (UTC)

There is an explanation at neutrino oscillation. As far as I understand it, the hypothesised neutrino mass eigenstates have different masses and so propogate at different velocities (because of conservation of momentum). The mass eigensates are, in turn, combinations of flavour eigenstates, and so the mix of flavour eigenstates varies along along the neutrino's path. Therefore the probability of observing a particular flavour eigenstate varies according to whereabouts along the neutrino's path you make your observation. Gandalf61 (talk) 09:24, 11 June 2008 (UTC)

To put this more directly, flavor and momentum form an uncertainty relation, so if you had made the uncertainty on momentum arbitrarily small then you'd have no way of determining what kind of neutrino it was and vice versa. Dragons flight (talk) 17:28, 11 June 2008 (UTC)

Blow job pregnancy

Can I get a girl pregnant if I cum in her mouth when having a blow job, cause it goes into her but does it just get digested or is there a risk it might find its way to her uterous? —Preceding unsigned comment added by Milkly man (talk • contribs) 09:25, 11 June 2008 (UTC)

No, there is no connection between the digestive system and the uterus. — QuantumEleven 09:34, 11 June 2008 (UTC)

However there is a risk of the transfer of STDs. There is also a (minor) risk of pregnancy if your semen goes near the vagina somehow. Probably the greatest risk for pregnancy is if you do somehting like kiss your girl after the act and then perform unprotected oral sex on her. All in all, unless you are in a committed relationship and both of you have been checked for STDs since you entered into that relationship, any form of unprotected sex is simply a bad idea. Nil Einne (talk) 10:20, 11 June 2008 (UTC)

Angela Ermakova got pregnt from Boris Becker after transfering semen from a blow job, so it is possible if somebody wants it to happen. [21]--Stone (talk) 12:24, 11 June 2008 (UTC)

So did JD's girlfriend in Scrubs. Quipquip (talk) 20:12, 11 June 2008 (UTC)

If memory serves, that wasn't a blow job, it was a poorly aimed premature ejaculation. --Tango (talk) 21:31, 11 June 2008 (UTC)

Indeed I probably should have said, unless you are in a committed relationship, have both been checked for STDs and are both ready to and have talked about how you will deal with an unexpected pregnancy Nil Einne (talk) 22:02, 11 June 2008 (UTC)

Hi. I'm not really qualified to answer this, but I think I once read somewhere (I forget where) that a girl in Lesotho who was unable to reproduce and gave a BJ, then her boyfriend got angry and stabbed her in the stomach thus allowing seminal fluid to seep into her uterus and she became pregnant. Thanks. ~AH1^(TCU) 23:34, 11 June 2008 (UTC)

That sounds unlikely. If the knife pierced the uterus, it would probably be unable to support a fetus. The semen may get in and fertilise an egg, but it wouldn't be able to go to term. I suppose the knife could have hit a fallopian tube, and the semen got in that way, and the uterus was left unharmed, but that still seems unlikely. Also, if she was unable to reproduce, the semen getting in via a knife wound is very unlikely to make any difference. She probably got pregnant the old fashioned way and then got stabbed, and the whole infertility thing was just incorrect and has made for an interesting, but erroneous, story. --Tango (talk) 23:55, 11 June 2008 (UTC)

Hypothetical Questions about Gravity and the Sun

Question 1: What exactly would happen if the sun moved 500 miles away from earth?

Question 2: What exactly would happen if the earth slowed its rotation speed by, say, 20 miles?

Please note that I am a 35 year old man and these are not homework questions. I would like to know exactly what I would experience when these phenomonas happen. --Vincebosma (talk) 13:03, 11 June 2008 (UTC)

You wouldn't notice a 500 mile change in the orbit of the Earth. The variation in distance caused by the orbit not being a perfect circle is about 5 million kilometres, so 800km would be insignificant. Question 2 doesn't make sense, do you mean 20 miles per hour? And by rotation speed do you mean the Earth rotating on its axis, or orbiting the Sun? --Tango (talk) 13:16, 11 June 2008 (UTC)

On its axis. And 20 mph. Also what would I experience if it slowed down say 200 mph? Forgive me for my serious lack of science knowledge. Just trying to answer questions my nephew is asking me. He's only 6. --Vincebosma (talk) 13:30, 11 June 2008 (UTC)

Assuming you mean the speed at the equator (which is the fastest - the poles don't move at all), the actual speed is about 1040 mph. Slowing that down would result in a longer day. 20mph is about 2%, so the day would be nearly half an hour longer, 200mph is 20%, corresponding a day nearly 5 hours longer. Lengthening the day would have all kinds of effects. Most would be fairly minor for just 30 mins longer, although some animals and plants may be confused. 5 hours would confuse pretty much everything. It could also affect the climate. One of the causes of prevailing winds is the Earth's rotation, so slowing that rotation could result in slower wind speeds. It would also result in a slight increase in gravity due to reduced centrifugal force (which acts to cancel out part of the gravitational force), but that would be negligible (it would just reduce the difference between the poles and the equator). --Tango (talk) 13:55, 11 June 2008 (UTC)

(After edit conflict) This is a good opportunity to introduce your nephew to orders of magnitude. The circumference of the Earth is roughly 25,000 miles. So a point on the equator travels a distance of 25,000 miles every 24 hours due to the Earth's rotation on its axis. This is a speed of about 1,000 mph - the speed of a supersonic jet. If you were flying in a supersonic jet which slowed down by 20mph, would you notice the difference ? If every hour was 61 minutes instead of 60 minutes, would you notice the difference ? The Earth is about 93 million miles from the Sun. Compared to this distance, 500 miles is about 5 parts in a million. A millionth of a mile is about 1/16 of an inch. If you had to walk a mile, and then someone increased the distance by 5/16 of an inch, would you notice the difference ? Gandalf61 (talk) 14:03, 11 June 2008 (UTC)

Thank you, and congratulations, for trying to answer his questions. Too many parents/uncles/aunts give the "Because God said so." or "Because it is, stop asking." To help you explain the answers by Tango and Gandalf, it may be helpful (and instructive, and get you two some valuable play time, and get you outside) to perform this exercise. Go outside with a basketball and a marble (or, if you're not that commited to scale, which isn't quite as important at his age a golf ball or ping pong ball will do). Have him put the basketball down where he wants the sun to be. Then, hand him the Earth ball (the smaller one) and tell him to put it where the Earth is. It should be 534 feet away, assuming the basketball is the size of the sun (Note that at this scale, the earth is 1/4 of an inch in radius). You may need to go about a block away...its not quite a backyard exercise. Now, to answer his question of what would happen if the Sun moved 500 miles. Have him move the basketball 1 inch, or have him roll the ball once around or whatever. (The actual amount of movement would be .03 inches, but thats not particularly visual for a 6 year old). Ask him if he thinks its made a big difference. EagleFalconn (talk) 14:21, 11 June 2008 (UTC)

As for question 1, the distance of the Earth from the Sun is determined by the orbital speed. If you moved them apart by 500 miles without increasing the orbital speed, this would result in the Earth "falling" back those 500 miles, in about 3 months, and then another 500 miles closer to the Sun, in the next 3 months, then it would turn around and go back out to the original point in the next 6 months. So, if you had started with a circular orbit, this would make it slightly elliptical. However, since the orbit of the Earth is already more elliptical than that, this would either increase or decrease the eccentricity of the orbit, depending on whether the 500 extra miles were added when the Earth was closest or farthest from the Sun. StuRat (talk) 14:44, 11 June 2008 (UTC)

To really screw with his head, explain the Milankovitch cycles which dictate that we're all gonna die even if the Earth stays in its current orbit. Ice age! EagleFalconn, thanks for your excellent outline of a practical, understandable demonstration. I'll be able to use that in another 4 years or so :) Franamax (talk) 14:51, 11 June 2008 (UTC)

Hi. Well, as for the sun moving 500 miles away, that depends on which way it moves. If it moves horizonal and along Earth's orbital plane, it would be 500 miles closer than normal 6 months later. If it moved verticly (north-south), it might not be exactly 500 miles as from the Earth. However, distance from the sun can affect the climate. For example, currently the Earth is closer to the sun in the southern hemisphere summer than in the northern hemisphere, so the southern hemisphere gets more summer sun intensity. I'm not sure, but if the opposite were true, as can happen with cycles lasting tens of thousands of years, the Sahara might green, for example, but things like Global warming may disrupt these cycles. However, if the centre of the Earth were only 500 miles from the sun, then part of the Earth would be in the sun, and if the surface of the Earth were that far, we'd be in the sun's atmosphere and be past its Roche limit, and fall into the sun. The speed of our orbit around the sun is determined by several factors, which I'm not too familiar with, but is most likely dictated by distance from the sun. However, if our orbit speeded up dramaticly for whatever reason, the Earth would fly away from the sun due to centrifugal force, then slow down because the sun's gravity there is weaker. If you need articles that are written in Simple English which might be easier to explain, you can check the languages box in the article to see if there is one. Thanks. ~AH1^(TCU) 23:30, 11 June 2008 (UTC)

As a clarification, yes, distance certainly as an absolute value has an effect on the amount of energy recieved by the earth. However, at the distance the earth is currently at, the amount of time and the directness of the striking of the sun's rays on the earth's surface as measured by the angle of insolation are much more significant factors.EagleFalconn (talk) 16:04, 12 June 2008 (UTC)

Rancid meat

Why can't you eat rancid meat if it is cooked? Surely if it is cooked really, really well then the heat will kill any bacteria, viruses or other germs that would make you sick. Pob The Plumber (talk) 13:41, 11 June 2008 (UTC)

Cooking the meat may sterilise it. But some toxins that were produced by the putrifactive bacteria survive the cooking process. Escherichia coli produces one such heat stable toxin. So dont eat last years, raw,forgotten Christmas Turkey now, cooked or not :-) Fribbler (talk) 14:05, 11 June 2008 (UTC)

Got it! Thanks. Maybe my mother-in-law would like a turkey sandwich..... Pob The Plumber (talk) 14:43, 11 June 2008 (UTC)

Just to clarify, rancid and putrid are not the same thing. One is oxidative decomposition, which makes things smell bad (rancid butter, rancid tuna), the other is a bacterial process. Nevertheless, if it's meat and it smells bad, throw it away. Franamax (talk) 15:01, 11 June 2008 (UTC)

One of the reasons why various cuisines developed highly-flavored/highly-scented/piquant sauces, of course, is...

Atlant (talk) 17:22, 11 June 2008 (UTC)

Why didn't all English gourmets and hunters die in centuries past from eating "high game" as discussed by Dickens [22] or in this 1889 book [23] or this recent publication [24] "The pheasant was not as well hung as the staff had told us and lacked the real oomph of high game." Apparently some gourmets still seek a "well hung" pheasant. Note: I strongly discourage eating rotten meat. Edison (talk) 20:44, 11 June 2008 (UTC)

Oh yumm, hare soup and make sure every drop of blood goes in it! Many meats are hung, for instance beef carcasses for 2-3 weeks, to allow the existing enzymes to partially "digest" the meat and soften it. Bacteria will grow only on surfaces, so the toxin load would not be high, and washing or boiling would handle it anyway (contrast with contaminated ground beef). Plus you need the right unlucky combination of toxin-producing bacteria and conditions under which the bacteria will be producing the toxin. I'm thinking that not all, but quite a few gourmets of ages past actually did die from eating spoiled food, they probably called it dropsy or something back then, before they figured out what was causing it. Franamax (talk) 00:37, 12 June 2008 (UTC)

Some mycotoxins in particular are nasty stuff. While they don't tend to be much of a problem on meat (well other then by meat from animals feed contaminated grains), they are a problem on grains and also fruit. Aflatoxin is one good example. As with bacterial enterotoxins and endotoxins, cooking does not destroy them so if you come across fruit or grains that look like they are moldy, throw them out. Particularly for anything soft as often what you see is only a small percentage of what is there. Nil Einne (talk) 22:00, 11 June 2008 (UTC)

Why don't we have 4 seasons every 27 days?

Hello giant minds! The Earth's 23.5 degree inclination pushes points on its hemispheres a few thousand miles either closer/farther from the sun causing seasons throughout the year. Shouldn't the Earth's massive "wobble" as it holds the Moon spinning around it cause the same effect? Earth orbits every 27 days or so (just like the Moon) around the barycenter of the Earth-Moon system, located thousands of miles from Earth's apparent center. Why am I not expecting snowstorms followed by beach weather every few weeks? Sappysap (talk) 15:06, 11 June 2008 (UTC)

The seasons happen because of tilt - the angle of the sun's rays to the Earth - not the distance. Those few thousand miles are insignificant for seasonal purposes. — Lomn 15:21, 11 June 2008 (UTC)

The reason is multi-fold. To address a common misconception you mention: The distance between the sun and the earth has almost no effect on the seasons. Between summer and winter, the change in the distance is about 3.1 million miles. However, the northern hemisphere's winter occurs when the Earth is closest to the sun. See [[25]] for more.

The first is the angle of insolation, which is the angle at which the sun's rays, directly striking the Earth's surface, strike the earth. The greater the angle, the less energy is transferred to the surface of the earth and its atmosphere. That is why summer occurs when the hemisphere you occupy is tilted toward the sun.

However, the Earth does not 'wobble' as the Moon revolves around it. The direction of the gravitational force between the moon and the earth does cause a center of rotation between the two of them, but that does not change the angle of insolation. There is no angle of insolation change due to the barycenter, though there is a slight distance change. However, if 3.1 million miles isn't making a difference, this certainly won't. EagleFalconn (talk) 15:27, 11 June 2008 (UTC)

For effects that are significant over the period of a month, see tide. --Prestidigitator (talk) 16:17, 11 June 2008 (UTC)

Sweating

A little background: I went for a bike ride the other day, it was about 15 degrees out, so I wore a t-shirt and some shorts to keep cool. During the bike ride, as is normal for me, I started sweating. This isn't much of a problem, but then this guy pulls up next to me on his bike wearing jeans, a sweater and a vest, and he's not sweating a bit. This blew my mind, as we were doing the same work--riding down the same street for essentially the same ammount of time, he on a mountain bike and me on a road bike, so I was actually doing a little less. What gives? Why was I sweating like a pig, and he not even uncomfortable? 142.33.70.60 (talk) 16:22, 11 June 2008 (UTC)

Just because he wasn't sweating doesn't mean he was comfortable. Some people just don't sweat much, which can make them overheat more easily. Also, weight makes a huge diff, as extra fat both provides thermal insulation and extra mass to move, requiring the burning of more calories. Cardiovascular fitness also makes a diff, as some people will be seriously stressed by that level of exercise while others "won't even break a sweat". StuRat (talk) 16:39, 11 June 2008 (UTC)

Assuming you meant it was 15°C, or 59°F, that seems cool enough that most people wouldn't sweat noticeably during a relaxing bike ride. StuRat (talk) 16:44, 11 June 2008 (UTC)

Also, maybe he hadn't been riding for as long as you? It takes a while after you start exercising for the body to produce enough excess heat to trigger sweating. —Ilmari Karonen (talk) 16:54, 11 June 2008 (UTC)

And if you were truly sweating "like a pig" you wouldn't be sweating at all, since they don't. Matt Deres (talk) 15:21, 12 June 2008 (UTC)

Cameras in rough times

Why do cameras often temporarliy show just noise when subject to violent vibrations? Example at 0:35. —Bromskloss (talk) 17:59, 11 June 2008 (UTC)

Theres a slight difference here between digital and film cameras, but the explanation is essentially the same. On a digital camera, when you press the button a sensor is triggered which takes a time average of (essentially) what color light is hitting the sensor at that particular pixel. If the camera is shaking, the average is going to be over a range of colors, usually resulting in a gray or other odd color, what you might call noise. On a film camera, its the same effect except instead of a detector you've got chemicals on a piece of film. The chemicals, being exposed to several different colors of light, will report all of them, which we typically see as white. EagleFalconn 18:20, 11 June 2008 (UTC)

Like motion blur, you mean? I don't think that's it. What I'm talking about looks more like the camera is about to fail completely, like if a signal cable is not properly plugged in, but spuriously loses contact. Mabye that's it – the signal cable losing contact? —Bromskloss (talk) 18:42, 11 June 2008 (UTC)

The sort of noise you see there is caused by a bad connection being vibrated so it isn't always transmitting a signal. --Carnildo (talk) 22:02, 11 June 2008 (UTC)

How come radio waves aren't stopped by walls and such?

You gotta ask to learn! If, for instance, AM waves have a wavelength of 100m to 1km (from Radio frequency), how come they can pass through walls and such? The way I see it is obviously wrong, so I'd be thankful for a few pointers, although I think that I've looked through the main articles. -- Aeluwas (talk) 18:05, 11 June 2008 (UTC)

The quantum mechanical view on it would be that for (1) photon to interact with an atom, that atom/molecule/whatever needs to have a valid energy transition available to it at the same energy as the photon or (2) the possibility for a Stokes collision.

For case (1), if the energy levels in the atom do not correspond to the energy of the photon, no interaction is allowed because no electron is available for promotion to a higher energy level. This rarely (I'm prepared to say never) happens with radio waves because the photons are of such low energy (a quantity which is inversely related to wavelength) that there are no electronic transitions available. Nuclear energy state transitions do occur in those areas, however those transitions are very difficult to achieve by inputting electromagnetic radiation and is better done with a magnet, as in NMR.

Case (2) There is a probability that an electron will 'collide' with a photon and remit the photon at the same wavelength or a different one. See Stokes shift. This is a very difficult effect to observe with radio waves, more so than with other types of light. In general, these collisions are very improbable and any experimentation with them has to be done with a laser to generate sufficient intensity so as to be able to collect data. EagleFalconn (talk) 18:33, 11 June 2008 (UTC)

I'll give a very general, non-technical answer. Because the walls aren't dense enough. Now if the walls were made of thick lead, then they would stop the radio waves. If you are in the center of a large building with lots of walls, or underground they would stop the radio waves too. ScienceApe (talk) 18:59, 11 June 2008 (UTC)

None of the above. There are two ways, both correct, to think of radio waves: either as oscillating electromagnetic (EM) fields or as photons. At the long wavelengths that you are talking about, the photon view is not helpful, and it is better to think of EM fields. An EM field is partly electric and partly magnetic, hence its name. In order to stop an EM wave, you need either an electrical or a magnetic barrier, or both. An electrical barrier needs to be an electrical conductor, like a sheet of copper or aluminium. A magnetic barrier is harder to achieve, but a layer of soft iron would work as both an electric and a magnetic barrier for low-frequency waves. Walls are generally made of neither electrical conductors nor magnetic materials, so they don't stop radio waves at the frequencies you are talking about.

Higher-energy radio waves (shorter wavelengths, like microwaves) behave more like light and are stopped by walls, but that's another subject. --Heron (talk) 20:04, 11 June 2008 (UTC)

I don't believe that is entirely true. Or at least saying I'm wrong isn't true. Putting a sufficient amount of matter in between you and the radio waves will stop them. If you were surrounded by say a kilometer of ice on all sides, it would block any EM radiation from getting in. ScienceApe (talk) 20:49, 11 June 2008 (UTC)

It is true that the shorter the wavelength is, the more like visible light the radio wave will behave, since the only difference between visible light and radio waves is that radio waves have a longer wavelength. I'm not sure microwaves are completely blocked by walls, though - if memory serves, the frequencies used by Wi-Fi are in the microwave range, and they certainly can go through walls, although the signal is noticeably weakened. --Tango (talk) 22:36, 11 June 2008 (UTC)

Going off what Tango said, I can confirm that microwave is not always stopped by walls since cell phones are run off of microwaves (hence the whole cancer/cooking your brain scare). However, using a material of a sufficient density/thickness is simply taking advantage of the Stokes collision effect I mentioned above. It works better with shorter wavelengths because shorter wavelengths tend to exhibit more particle like behavior (hence why walls are not transparent). Another more satisfying way to think about it (for me at least) is that shorter wavelengths are more likely to be in the correct range of energy states to be able to interact with the wave function defining the translational motion of the nucleus/electron cloud of the atom. EagleFalconn (talk) 16:12, 12 June 2008 (UTC)

Actually, the absorption scale for radio waves in ice is many tens of km. For example, radar reflections are used to measure the shape of the bedrock under the ice at Antarctica. Also, in line with Heron, the limiting factor is still conductive impurities (mainly sulfates and H+ ions) and not bulk matter per se. Dragons flight (talk) 22:30, 11 June 2008 (UTC)

More like 5 KM actually. Nope, it really is bulk matter. You can take any matter and if you surround yourself with enough of it, it will block EM radiation. Denser material is better at stopping EM radiation than less dense material. ScienceApe (talk) 23:34, 11 June 2008 (UTC)

Strictly speaking denser is better, but free electrons (e.g. metals and ions) have a much, much greater effect on absorption/scattering than density. Dragons flight (talk) 00:10, 12 June 2008 (UTC)

A thin layer of iron, steel. or even iron hardware cloth will interrupt most AM or FM radio broacdasts by acting as a Faraday cage. By thickness, ferrous metal provides far better radio shielding than brick, rock, or concrete. Edison (talk) 20:31, 11 June 2008 (UTC)

Um, doesn't the thin layer of this stuff have to be somewhat enclosed? You can't really have no charge on the inside if there is no "inside". --Wirbelwindヴィルヴェルヴィント (talk) 04:13, 12 June 2008 (UTC)

Yes, it does need to be enclosed. EagleFalconn (talk) 16:12, 12 June 2008 (UTC)

You might enjoy our article about TEMPEST, a U.S. military standard that is deeply involved with exactly how well walls stop radio emissions.

Atlant (talk) 12:25, 12 June 2008 (UTC)

Uh, yeah, if it is not a closed surface it is not a Faraday cage. But a large sheet of metal could provide some directional degree of shielding, as could a metal surface with some holes in it, or a curved metal surface. A metal surface or rod could also increase the field strength, if it happened to be where it was a director or reflector, depending on the location of the transmitter and receiver, like in antenna design. Edison (talk) 18:59, 12 June 2008 (UTC)

The Radius of the Earth

Is it possible to calculate the radius of the earth simply by measuring the time between two sunsets, one observed by lying down and the other observed by standing up just after the sun (apparently) goes down while we were lying down?? If so, how?? —Preceding unsigned comment added by 117.194.226.115 (talk) 18:18, 11 June 2008 (UTC)

Have you tried drawing a picture of the scenario? -- Coneslayer (talk) 18:33, 11 June 2008 (UTC)

Yes. For an observer standing on the surface of the earth, his line of vision in both cases are tangents to the earth's surface. The sun covers 360 degrees in 24 hours, so supposing the time interval between the two sunsets is x seconds, we can calculate the angle covered by the sun in that time. But does that really help? I'm completely lost as to what to do after this. —Preceding unsigned comment added by 117.194.226.115 (talk) 18:38, 11 June 2008 (UTC)

This webpage explains the experiment: http://astronomy.nmsu.edu/nicole/teaching/ASTR110/lectures/lecture10/slide05.html . The experiment can be performed either at sunrise or sunset. If you measure the height of the standing person, denoted h (cm), and the time between the sunsets, denoted ΔT (s), then the radius of the Earth, denoted R (cm), can be found by the equation:

$R=h\cdot {\frac {\cos(\triangle T/240)}{1-\cos(\triangle T/240)}}$.

Convert R to more sensible units of meters or kilometers by dividing your answer by 100 or 100,000 respectively. Jdrewitt (talk) 20:48, 11 June 2008 (UTC)

Keep in mind that you should do this only where you have a true horizon (like watching the sun set over the ocean). Mountains, trees, or other large and relatively close obstacles are going to mess up the experiement completely. --Prestidigitator (talk) 21:06, 11 June 2008 (UTC)

Also keep in mind that atmospheric diffraction distorts the apparent positions of the Sun and the horizon. I don't know if this will have a noticable effect on the experiment, but when dealing with things as small as the timing differences involved here, it's worth thinking about. --Carnildo (talk) 21:59, 11 June 2008 (UTC)

I think you mean atmospheric refraction, not diffraction. -- Coneslayer (talk) 14:25, 12 June 2008 (UTC)

Thank you so much! I get it now! —Preceding unsigned comment added by 117.194.225.178 (talk) 05:46, 12 June 2008 (UTC)

Note that I'd expect the margin of error to be absolutely huge, so consider yourself lucky if you get the answer within an order of magnitude. Also, you'd need to consider that the time between two consecutive sunsets isn't exactly 24 hours anyway, depending on whether the days are getting longer or shorter. StuRat (talk) 04:35, 13 June 2008 (UTC)

Good point -- so it's better to observe the same sunset twice. Lie down, watch it set and start your stopwatch, then quickly stand up and do it again. If you do it at sunrise you can quickly drop to the ground instead of quickly standing up. Or have two people do it together, one in each position. --Anonymous, sitting down, 05:45 UTC, June 13, 2008.

Yeah, it's probably impractical with a height of 6 feet or so, but it's really cool from an airplane. I once watched the sun set while were taxiing, then we took off and I watched the sun come back up over the horizon, then it set again. It's like that old ad (for Life Savers?) with the kid saying, "Do it again, Dad!" -- Coneslayer (talk) 11:18, 13 June 2008 (UTC)

And even cooler, if you are in a plane going West fast enough, you can apparently make time go backwards and make the Sun rise in the West and set in East. This would require supersonic speeds at the Equator (over 1040 MPH), but much less at the Arctic or Antarctic circles. StuRat (talk) 12:24, 13 June 2008 (UTC)

Hottest time period in Earth's history

What was it? I have heard it may have been the Middle Cretaceous or the early Eocene, (Paleocene–Eocene Thermal Maximum), but from climate graphs of the earth, it is hard to tell because many periods are warm and I can't seem to find an exact answer. Thanks 142.150.72.199 (talk) 18:23, 11 June 2008 (UTC)

Hi. Well, I'm not sure, but I think it may have been sometime around the Hadean eon in the Precambrian, when the earth just recently formed, the crust was not yet solid, and the Earth was experiencing the Great Bombardment. However, if you include the future, there may be periods hotter than some mentioned above. Hope this helps. Thanks. ~AH1^(TCU) 23:08, 11 June 2008 (UTC)

Thanks, but I was more so asking about the climate a time period so far where there was life and ecosystems, particularly, animal life. 192.30.202.21 (talk) 22:35, 12 June 2008 (UTC)

Hi. Does this this graph help? It graphs temperatures throught the time periods but with the present at the left and the far past at the right. Also note that it goes to the beginning of the Cambrian 542 million years ago. Thanks. ~AH1^(TCU) 00:52, 14 June 2008 (UTC)

I'm guessing that just when the Earth was formed, and was still molten magma all over would have been a pretty hot time. —Pengo 20:30, 14 June 2008 (UTC)

Planet orbit question and the formation of our solar system

Are all the planet in our solar system revolving around the sun in the same direction? Are they all rotating/spinning in the same direction? If not, how is this possible? During the formation of our solar system, shouldn't they be revolving and rotating in the same direction due to the conservation of angular momentum? ScienceApe (talk) 19:02, 11 June 2008 (UTC)

All of the planets revolve the sun in the same direction: from the north pole of the sun, counter-clockwise. All the planets except for Venus also rotate counter-clockwise (again looking from the sun's north pole). See solar system, Venus, and formation and evolution of the solar system for more details. Jkasd 19:28, 11 June 2008 (UTC)

With regards to angular momentum and the formation of the solar system, how or why is Venus spinning clockwise? ScienceApe (talk) 20:25, 11 June 2008 (UTC)

Nvm, it seems like an impact event caused it. ScienceApe (talk) 20:26, 11 June 2008 (UTC)

Also, Uranus's axis is inclined at 98 degrees. And also see retrograde and direct motion. Jkasd 19:40, 11 June 2008 (UTC)

Perhaps yours is, butt not mine ... StuRat (talk) 04:27, 13 June 2008 (UTC)

I've often wondered why they would say the axis is rotated 98° and it's rotating in the normal direction, instead of saying it's axis is rotated 82° and it's rotating backwards. StuRat (talk) 04:27, 13 June 2008 (UTC)

I would guess it's because chances are it started rotating in the normal direction and then got knocked over by more than 90 degrees, rather than it reversing its direction. --Tango (talk) 13:00, 13 June 2008 (UTC)

That is surely how it happened, but it doesn't explain why people use that way of describing it. Really it's just an arbitrary choice. --Anon, 22:15 UTC, June 13, 2008.

Yeah, so depending on how you look at it, Uranus can have retrograde motion or not. Jkasd 01:08, 14 June 2008 (UTC)

Weight of human hair

How much does one's head hair weigh? More precisely, is there a formula that can be used to estimate the weight of head hair based on length(and accounting for differences in hairline, bald spots, and such)? 69.111.189.55 (talk) 22:20, 11 June 2008 (UTC)

You can always shave it off and put it on a scale. Paragon12321 (talk) 21:11, 12 June 2008 (UTC)

If you ask a hairdresser very nicely and say it's for a science project to give it cred, they will let you collect the day's hair takings. Wear surgical gloves and bag it neatly to impress, Julia Rossi (talk) 01:04, 13 June 2008 (UTC)

My guess is that given the differences you've already mentioned (in hairline etc) combined with other differences (like in thickness of the hair), any general formula will be pretty useless Nil Einne (talk) 03:42, 14 June 2008 (UTC)

Flammable cleaning products

(No, I'm not a vandal.) Hello. What are the most flammable cleaning (or otherwise) products that a janitor could use in his work? (No, I'm not a janitor either.) Thanks in advance, Kreachure (talk) 23:15, 11 June 2008 (UTC)

Toluene would rank right up there, or any other solvent the janitor might be using for some purpose. Most chemicals and commercial products have a safety data sheet, googling the name plus "msds" will usually get you some good data. Franamax (talk) 00:50, 12 June 2008 (UTC)

Toluene has a very low flash point, but alcohols such as ethanol or isopropanol have much lower autoignition temperatures. However, the most flammable, common solvent is probably diethyl ether. Not sure if this would be found in many janitor closets, though. --Russoc4 (talk) 03:28, 12 June 2008 (UTC)

I suspect that among the more dangerous solvents a janitor might try to use would be plain old gasoline. In addition to being rather toxic, it's acutely flammable and its vapors are easily ignited by spark or open flame. Other flammable chemicals likely to be found in a janitor's closet might include various solvents used as paint thinners: acetone, turpentine, xylene.

If you're writing a story and need ideas, you might just walk down to your local hardware store—find the products with the scariest warning labels. TenOfAllTrades(talk) 05:10, 12 June 2008 (UTC)

You're right on the money. Thanks for the tips! Kreachure (talk) 19:11, 12 June 2008 (UTC)

June 12

Succession in Commmunities

What happens to the number of kinds of plants as the years pass? —Preceding unsigned comment added by 72.67.191.161 (talk) 03:13, 12 June 2008 (UTC)

The number of species of plants on Earth has increased from zero to many millions. A more specific answer will require a more specific question. --Sean 13:51, 12 June 2008 (UTC)

automatic sphygmomanometer

How does the machine measure the diastolic reading ? In manual readings it is when the sound of the pulse dissipates.Thommo123 (talk) 03:36, 12 June 2008 (UTC) Paul

See Korotkoff sounds. If the machine pumps the cuff pressure up sufficiently high and then slowly releases it, the point will come when Korotkoff whooshing sounds are heard at the brachial artery, at the pressure when the systolic pressure is sufficient to force blood through the restriction caused by the cuff. The K sounds continue with each heartbeat as the pressure drops until the diastolic pressure is reached, at which point the K sounds stop. Blood pressure machines I have dealt with just record the sound from the microphone and the pressure, and sends these two pressures to the readout. A comparator or trigger circuit can monitor the microphone sounds to decide when the K sounds are being produced. Edison (talk) 04:00, 12 June 2008 (UTC)

What about the ones that give continuous blood pressure readings? Surgeons on TV are always saying "BP's dropping", and they aren't constantly pressurising and unpressurising a cuff, as far as I can tell. --Tango (talk) 14:28, 12 June 2008 (UTC)

BP measured as described, by a trained human, with a mercury manometer, is be considered to be very accurate. It can also be a flawed measurement, if apprehension about the test causes an increase in BP. A continuous measurement at least avoids that stres, but may be more of an approximation, with computerized corrections, per Blood pressure, based on an external pressure transducer. Edison (talk) 18:54, 12 June 2008 (UTC)

Berembang tree

What is a berembang tree? I know it is in Malaysia. I also know that fireflies thrive on it and twinkle among the berembang trees like lights on Christmas trees. But that is all that i know. Any help......

TCGKennedy —Preceding unsigned comment added by TCGKennedy (talk • contribs) 04:00, 12 June 2008 (UTC)

The Berembang tree also known as the Crabapple Mangrove is botanically called Sonneratia caseolaris. You can find mor information about it at this link. [26]and some photos here [27]

Richard Avery (talk) 06:49, 12 June 2008 (UTC)

I believe these are common in Kuala Selangor which is well known for its firefly park [28] [29]. It sounds a bit like what you're referring to Nil Einne (talk) 09:58, 12 June 2008 (UTC)

Modeling a Body Moving in a Fluid

I am not a Physics expert so I can only say that this is a Fluid Dynamics question but I don't even know where to look for this specific equation or what is it called. Basically, we already know that the faster a car moves (in air of course), the lower its MPG becomes because it takes more energy. This is the same as if I filled a bathtub with water and tried to move my hand through it. If I move slowly, it is easy. The faster I try to move, the harder it becomes. So my question is, is there a page on wikipedia (or in one of the books) or even somewhere else online, which talks about the general form of this equation (preferably with the constants gives)? I just want to know what exactly happens to my MPG as I increase my speed on the highway. I can guess that it decreases exponentially but how rapidly. If I double my speed, how does my MPG change? Thanks!69.232.109.213 (talk) 04:45, 12 June 2008 (UTC)

Drag (physics)#Drag at high velocity is probably what you want, along with Fuel economy in automobiles#Physics background. AlmostReadytoFly (talk) 09:18, 12 June 2008 (UTC)

Thanks, this is exactly what I was looking for.68.126.127.207 (talk) 03:13, 13 June 2008 (UTC)

Robotic spacecraft maintains air pressure?

Does Robotic spacecraft maintain air pressure inside? If yes, what are benefits of air inside? I can think of using circulating air to control temperature inside. If air escapes in space, will there be any problem? —Preceding unsigned comment added by Ranemanoj (talk • contribs) 04:42, 12 June 2008 (UTC)

Generally no, but this may vary by design (though I can't think of any such designs offhand). Maintaining pressure means adding weight, something all spacecraft avoid where possible. Additionally, air is actually a rather lousy means of transferring heat -- metal conducting or radiating heat is preferable. Air unexpectedly escaping into space would result in unexpected thrust, which would have to be countered with fuel expenditure. — Lomn 08:02, 12 June 2008 (UTC)

If air is not desired, before launch, is it pumped out thereby creating vacuum inside spacecraft? Can is be designed such that, before take off from earth, spacecraft contains air, but as it goes up in low pressure air or space, air goes out gradually without creating thrust? Are there any instruments which are sensitive to pressure which may malfunction due to loss of air? 203.129.237.147 (talk) 11:25, 12 June 2008 (UTC)

If memory serves, Sputnik 1 was pressurised. I don't know of any other unmanned (and unanimaled!) space craft with internal pressure. All you need to do is make sure it isn't air tight, and the air can escape as it launches - the trust would be insignificant if it happens during launch when you have air resistance and rocket motors producing far more force. Also, if it escapes evenly from all sides, the trust will cancel out. They might pump the air out just to be on the safe side, I don't know, but I wouldn't think it was essential. --Tango (talk) 14:23, 12 June 2008 (UTC)

The laser diodes of some spacecrafts are sealed and contain dry air, because optical sufaces are sensitive to the change of atmosphere. Normally all Instruments on a satelite have to proofe that they are capable to vent the atmosphere within during launch. Stable compartments which can hold vacuum or normal eart atmosphere are a lot of mass and are avoided.--Stone (talk) 14:57, 12 June 2008 (UTC)

Martian North Pole

Just a quick question...When it is said that the Phoenix probe is on the north pole of Mars, I assume they mean relative to Earth's north pole? (Which is really the south magnetic pole...) I've also heard 'the north pole of the sun', this has the same meaning?--Shniken1 (talk) 04:59, 12 June 2008 (UTC)

That's a really good question. Seriously. Wiki has a detailed article discussing the various definitions of the poles of astronomical bodies, which answers your question very nicely. In brief, yes, the standard definition is as you say, but it is not the only one possible. Best regards, --Dr Dima (talk) 05:57, 12 June 2008 (UTC)

Actually, the Earth's North pole is the Earth's magnetic North pole as well. The pole of the magnet that gets attracted to the Earth's North pole is named as the magnet's North pole. In fact, the North pole of the Earth is the pole in which all magnetic lines of force converge. So a magnet's North pole point's to the Earth's North pole. In case of a magnet, the North pole is the pole from which the magnetic lines of force diverge. 117.194.226.11 (talk) 09:37, 12 June 2008 (UTC)

Yes, but if you consider the Earth as a magnet (it functions much like a bar magnet, if you don't look too closely), the Earth's magnetic north pole would be the magnet's south pole. This is due, I believe, to lazy people changing the English language - what we call the "north pole" of a magnet was originally called the "north seeking pole", which makes much more sense. --Tango (talk) 14:20, 12 June 2008 (UTC)

Except...Mars doesnt have a planet-wide magnetic field, so it has no "magnetic north pole". The only pole on Mars is the rotational pole, and as you say, it is only North because it is in roughly the same direction as our own magnetic north pole.

I wonder in the future, when we first visit another solar system, which way will be consider "north"? -RunningOnBrains 21:09, 12 June 2008 (UTC)

Probably the same way we do in this solar system - the direction closest to Earth's north. --Tango (talk) 21:21, 12 June 2008 (UTC)

One could also use the angular momentum vector of the planet to unambiguously define a north and south pole. Outstairs (talk) 06:40, 13 June 2008 (UTC)

Huh? The north magnetic pole is located near Ellef Ringnes Island in Nunavut. That's below 80N. The south magnetic pole is located near 65N so how are these exactly at the poles? Thanks. ~AH1^(TCU) 00:57, 14 June 2008 (UTC)

Did anyone claim the magnetic poles were exactly at the geographic poles? If they did, they were completely incorrect, but I can't see anyone claiming that. --Tango (talk) 15:44, 14 June 2008 (UTC)

Similar to the answers from Tango, Dr Dima and Outstairs, my reply to a related question at Talk:Phoenix (spacecraft)#Northern hemisphere followed the definition from poles of astronomical bodies and does not depend on magnetism:

See Poles of astronomical bodies, which has "The north pole is that pole of rotation that lies on the north side of the invariable plane of the solar system". The north side is that determined by the Earth's geographic north "side". So looking at the solar system from "above" (think of a spaceship launched from Earth's north pole straight up), looking "down" one sees all the planets' rotational North poles.

In turn, the Earth's geographic north pole does not need to depend on magnetism either, but is just defined historically (by Northern Hemisphere dwellers).-84user (talk) 14:23, 14 June 2008 (UTC)

I think all the talk about magnetism was just an aside. --Tango (talk) 15:46, 14 June 2008 (UTC)

Baseball

Hello. A pitcher throws a ball at 28 m/s [S] toward a batter. The ball contacts the bat for 2.0 ms and leaves the bat at 46 m/s [N]. What is the displacement of the ball when contacting the bat? The answer key multiplied the average velocity by time. Why? Thanks in advance. --Mayfare (talk) 06:00, 12 June 2008 (UTC)

Why what? --Dr Dima (talk) 06:05, 12 June 2008 (UTC)

I think Mayfare's asking why "the answer key multiplied the average velocity by time". But what I don't get is what is the question in the first place, as in, what do we have to calculate here? 117.194.226.11 (talk) 09:31, 12 June 2008 (UTC)

If the answer did indeed multiply the average velocity by a time then it would have produced a distance, and it is not at all clear how this could be a physcially meaningful quantity in this scenario. I suspect there may be a numerical coincidence here somewhere. It would help to know the units in which the answer was given (as well, of course, as knowing the full question, as pointed out above). Gandalf61 (talk) 09:50, 12 June 2008 (UTC)

Perhaps it's a misapprehension of the calculation. The average acceleration of the ball is Δv/t = (28 + 46)/2ms. The average of the speeds is (28+46)/2.

What was the question on the paper? AlmostReadytoFly (talk) 10:34, 12 June 2008 (UTC)

The speed averaged over what? You need to know how long it's travelling at each speed. Also, the question said average *velocity*, so you need to throw a minus sign in there somewhere. --Tango (talk) 12:39, 12 June 2008 (UTC)

Not averaged over anything. The point was that a naïve misinterpretation of the answer could be the reason for confusion. AlmostReadytoFly (talk) 13:20, 12 June 2008 (UTC)

Ah, sorry, you said "average of the speeds", not "average speed", my bad. It's a fairly meaningless number, though. --Tango (talk) 14:17, 12 June 2008 (UTC)

The question is asking how far the ball traveled while it was still in contact with the bat. The average velocity it traveled at while on the bat is (46 - 28)/2 (assuming contant acceleration for simplicity) the dispalcement is then the average velocity multiplied by time. -- Mad031683 (talk) 19:41, 12 June 2008 (UTC)

So if it left the bat at the same speed that it arrived (say 28 m/s in both cases), you'd have an average velocity of (28-28)/2 = 0 m/s, and you would calculate a distance of 0 m no matter how long it was in contact. I'm still not seeing the physical significance of this calculation. -- Coneslayer (talk) 19:50, 12 June 2008 (UTC)

The physical significance is the distance between where the bat starts and where it finishes. In your example, the bat would move backwards as it slows the ball down, and then forwards as it speeds it up in the other direction, ending up at the same place it started, hence the 0. In the case given by the OP, the bat would end up further forward than where it started. This is all assuming constant acceleration, though, which seems very unlikely to be even approximately true. In my experience of hitting balls, the bat moves forward far more than it moves back, regardless of the difference in speeds, this is probably because the bat is already moving before it contacts the ball. Keeping the bat still until the ball hits is more the ball bouncing off the bat than you hitting the ball with the bat. --Tango (talk) 19:57, 12 June 2008 (UTC)

Covalent Bond

I am a little confuse at the definition of covalent bond,it is the bond formed due to the sharing of electron,i say how is it possible becoz electron has the same charge they should repel each other how atom share orbitals (electron) —Preceding unsigned comment added by 202.125.143.78 (talk) 06:25, 12 June 2008 (UTC)

Covalent bonds do indeed share electrons and this is because electrons are actually more happy to be in pairs than they are on their own. I don't really know how this works out, I too would have thought they'd repel each other but i'll leave that to someone else. Regards, CycloneNimrod ^talk?_contribs? 06:44, 12 June 2008 (UTC)

(ec) Electrons certainly seem like they should repel each other because they have the same charge, but electrons in orbitals can be more stable when paired. Crazy, eh? Electrons have a quantum property called "spin" that can be either of two values, and an orbital can hold one of each: a spin-paired set is often more stable than a single electron in an orbital. The idea of two electrons (of opposite spins) per orbital isn't limitted to covalent bonds, by the way: consider how you do electron configuration for individual atoms, with two s electrons, etc. DMacks (talk) 06:51, 12 June 2008 (UTC)

Electrons do indeed repel one another! Please keep in mind, however, that for a covalent bond to be formed, you must also have at least two atomic nuclei in the neighborhood. And while these nuclei are electrically repelling one another, they are also electrically attracting all the electrons in the neighborhood! So things settle down into this nice snuggly, er, that is low potential energy arrangement we call a covalent bond. It's only when people ask questions about why the arrangement isn't even snugglier than we observe that you need to invoke things like the Pauli exclusion principle. --arkuat (talk) 10:28, 13 June 2008 (UTC)

The most powerful earthquakes...

...occur on Destructive Plate boundaries. Am I right? Thanks 79.78.3.4 (talk) 07:32, 12 June 2008 (UTC) (Moved from Humanities) 79.72.162.214 (talk) 09:46, 12 June 2008 (UTC)

Some of the most powerful earthquakes, though rare, occur in the middle of current plates. See New Madrid Seismic Zone as an example. This particular zone is on an ancient "failed rift" that never evolved into a plate boundary. -Arch dude (talk) 11:52, 12 June 2008 (UTC)

All the most powerful earthquakes, M_w 9.0 or greater, since 1900 have occurred on destructive plate boundaries, see our article Megathrust earthquake. Mikenorton (talk) 09:19, 13 June 2008 (UTC)

Science do not solve all of man's problems

I was aked to state my opinion on whether or not I agree with the above mentioned statement 'science do not solve all of man's problems.

i simply said, "issues in today's society or environmentally/ globally even!!!always seems to have some sort of scientific reasoning behind it.How ironic that as a people we are put together to work colaboratively, but wait if there is too much friction, we do have a solution its called proven speculation namely science..what happened to reasoning"

Now I am required to elaborate on this statement.

My question to you is 1. help me to elaborate and give facts to my statement. 2. Give and enlighten me on your opinion and what you would of said (provide). 3. A answer with an opinion that differs from mine.

Thank you in advance

Regards

Miss Inquisitive —Preceding unsigned comment added by 41.241.47.178 (talk) 10:41, 12 June 2008 (UTC)

Although this post seems like homework, do research whether the level of knowledge regarding the conception and birth of a human child has any effect on people's views on abortion. That would be a case where people can know the relevant scientific facts and yet still disagree on an issue.--droptone (talk) 11:37, 12 June 2008 (UTC)

I recommend you think about what science is not. For instance I would say that science cannot solve ethical problems. AlmostReadytoFly (talk) 13:25, 12 June 2008 (UTC)

That there are problems that science cannot solve is [1] obvious, and [2] unremarkable. A more interesting question would be, "Are there problems which are solved better by something other than science?". It would be fun to argue that everything that is not science is equally ineffective as science at "solving" ethical problems. - Nunh-huh 16:52, 12 June 2008 (UTC)

Your first step there is to define "solve". --Tango (talk) 18:54, 12 June 2008 (UTC)

blood

who invented the blood —Preceding unsigned comment added by Anandh heart (talk • contribs) 13:07, 12 June 2008 (UTC)

Nobody. We've always had blood. There's no individual who discovered blood either, as people have been injuring themselves and others since prehistory. AlmostReadytoFly (talk) 13:40, 12 June 2008 (UTC)

Firstly, as AlmostReadytoFly pointed out, blood cannot be invented, moreover, just because of the injuries, even animals that came to existence before humans must have noted it. —KetanPanchal^taLK 13:56, 12 June 2008 (UTC)

You could take a look at intelligent design, if you really want to. --Tango (talk) 14:16, 12 June 2008 (UTC)

And if you are actually asking who discovered the circulation of blood, see Ibn al-Nafis, Michael Servetus and William Harvey. Gandalf61 (talk) 14:22, 12 June 2008 (UTC)

There are some new artificial blood. Wasn't a single person who created them though. ScienceApe (talk) 15:24, 12 June 2008 (UTC)

S/he's not actually asking anything. This 'question' was posted on the Entertainment desk at the same time. You shouldn't waste time with this one, but I'm not the boss of you. -.-; Kreachure (talk) 15:55, 12 June 2008 (UTC)

We are obviously very literal here at WP:RD/S. The responses to this question at WP:RD/E are more ... umm ... creative. Gandalf61 (talk) 16:02, 12 June 2008 (UTC)

Exponential equation, solve for I0?

I have been struggling for some time (like 2 years pretty much!) to solve the equation given below for $I_{0}$:

$I=I_{0}\cdot e^{I_{0}\cdot t}$

I have tried to use Lambert's W function to find $I_{0}$, however the solution does not converge at the high values of $I$ that I am using. The equation is used to correct the measured signal intensity $I$ for a given detector deadtime $t$.

How can I solve this equation without using Lambert's W function (Which doesn't work). I'm sure (and really hope) that there is a much more simple way of solving this. Thanks Jdrewitt (talk) 16:49, 12 June 2008 (UTC)

I doubt that can be solved without using Lambert's W function. Lambert W function#Evaluation algorithm gives some ways to calculate its value outside the disc of convergence of its Taylor series, does that help at all? --Tango (talk) 17:16, 12 June 2008 (UTC)

I'll give it a go, since the evaluation algorithm section links to the desy webpage, there is a good chance that they developed it to try and solve a similar deadtime problem. Thanks, Jdrewitt (talk) 17:49, 12 June 2008 (UTC)

Since you aren't going to get a better closed-form solution than with W, why not just solve the equation numerically? I'm assuming that all your variables are positive (since you talked about I being "large"): then the function on the right is strictly increasing with $I_{0}$, and you should be able to apply something trivial like bisection search to it. (Since you're starting with the unbounded interval $[0,\infty )$, you'll have to start with some sort of interval-widening until you bracket the solution: evaluate the sign of $I-I_{0}e^{I_{0}t}$ at 1, 2, 4, 8, ..., until it changes (to negative) and then do the bisection search on $[2^{n},2^{n+1}]$.) Of course, other approaches like Newton's method might work better, but Newton's method in particular seems to converge very slowly for this function (18674 iterations with $t=3,\,I=5\times 10^{5},\,\varepsilon =10^{-6}$ like I tried). --Tardis (talk) 23:49, 12 June 2008 (UTC)

There are several numerical methods implemented as computer programs like Newton Raphson which are used for solving large matrix equations like tohse describing a power system which do not have a determinate solution. You may wind up with a small error term if you are successful. There are ways of determining whether you have found a good solution, and tricks for approaching that solution. I greatly admire those who are comfortable with such mathematics. I just use it. Edison (talk) 04:05, 13 June 2008 (UTC)

Magnetic monopoles and turning matter into energy

It seems that magnetic monopoles potentially can turn matter into energy. Is this process 100% efficient? Can it perform 100% conversion like antimatter? Will any of the energy be released as harmless neutrinos like in antimatter-matter reactions? ScienceApe (talk) 18:54, 12 June 2008 (UTC)

Given that the existence of magnetic monopoles remains conjuncture and speculation, much less their actual behavior, no answer can be given. — Lomn 19:26, 12 June 2008 (UTC)

Not even theoretical predictions? If we assume proton decay takes place? ScienceApe (talk) 20:50, 12 June 2008 (UTC)

Various grand unified theories do predict that magnetic monopoles will catalyze nucleon decay. I think the decay modes are the same as without the monopole, e.g. $M+p\rightarrow M+e^{+}+\pi ^{0}\,$ where M is the monopole (see proton decay). Whether this could be turned into a safe energy source I can't say. It's not "100% efficient", but neither is matter-antimatter annihilation—not all of the energy comes out as photons and you can't turn the photons into useful work with 100% efficiency anyway. -- BenRG (talk) 22:49, 12 June 2008 (UTC)

But will it turn a given piece of matter into its energy equivilant. And will any of that energy be in the form of neutrinos? ScienceApe (talk) 02:05, 13 June 2008 (UTC)

Eye myopia

I just recently got glasses for my myopia. I heard that the more you wear your glasses/contacts, the "lazier" the eye muscles get, making them more dependent on the corrective agents, thus making your vision worse. Is this true? I want to wear my glasses, but not at the expense of my eyesight. DISCLAIMER: NOT MEDICAL ADVICE (AND ALL THAT BLAH BLAH BLAH)...JUST WANT TO KNOW THE SCIENCE BEHIND IT. Thanks for your help. --71.98.22.225 (talk) 21:33, 12 June 2008 (UTC)

I've heard the opposite... I believe that, in some cases, wearing correct lenses can help your eyesight improve. I'm not sure what those cases are, though. --Tango (talk) 21:40, 12 June 2008 (UTC)

Unlike eyeglasses, contact lenses can mold the shape of the cornea, at least temporarily.Scray (talk) 01:57, 13 June 2008 (UTC)

What you heard doesn't sound well-informed. Are you thinking vision therapy? Applies to some conditions... Julia Rossi (talk) 09:40, 13 June 2008 (UTC)

Need Help in Finding an article previously found in Wikipedia

Wikipedia has an article that I recently read about an unusual mental condition in which a person can see spoken words, musical notes etc. in the air. And sometimes in colors. And in some individuals the colors are different depending on whether the other person speaking the words has a change in his/her emotions.

The Wikipedia article went on to give a fairly long list of famous people, both past and present, with this condition. George Gershwin was mentioned. Possibly Leonard Bernstein, other artists and composers.

I would greatly appreciate your advising the name of this mental condition.

BMany thanks,Bob Christman at <email removed - see page header> —Preceding unsigned comment added by 65.13.109.109 (talk) 22:40, 12 June 2008 (UTC)

I'd guess you were looking at Synesthesia, or the associated article List of people with synesthesia. Confusing Manifestation(Say hi!) 22:47, 12 June 2008 (UTC)

June 13

Any ideas on how to create a concrete sign?

Sorry I wasn't sure where to place this, but I thought science would be good because of physics/construction. So, I'm trying to create a concrete sign for a community organization. This is the type of signs I mean: http://www.centurygrp.com/precast_detail.asp?id=1

It doesn't need to be as "showy" as some of the ones on there, but still it's going to be a decent sized concrete sign. Problem is, I'm not really great at this stuff, and I'm not sure how to get started. I already have a location to construct this on (the base is present). I'm figuring I'd need to use bricks to create the frame around the sign. Would I need metal supports or something in the inside? Also, I have no idea on how to create the sign itself. Any suggestions will be much appreciated.

Thank you very much. —Preceding unsigned comment added by Legolas52 (talk • contribs) 04:33, 13 June 2008 (UTC)

These signs look highly developed. Without knowing what you expect to do (such as lettering in the concrete or external to it, colouring the concrete with pigments before mixing, the dimensions etc), there are companies via google that sell many styles of molds from precast stone and timber onwards (search precast concrete molds); you can even talk to them via email to research your project, and we have a tiny article Precast concrete for background. If yours is a tight budget and a rustic finish is acceptable, you can form by cutting a shape into earth and pouring directly or avoid casting by making a brick structure that you are happy to render. You can make a form box the size and shape you want, pour cement into it and presto – use an angle grinder and coarse metal file for finishing touches. Pigment colours are mixed dry before adding water etc. Your local hardware store could help with questions too. Hope this helps, Julia Rossi (talk) 09:13, 13 June 2008 (UTC)

And let me add, if it isn't already obvious, that the face of the sign would be in the bottom of the mold or form. The cheapest way to create a form would be to carve it out of Styrofoam, but this might not hold up to the weight of a thick concrete sign. You could put liquid or powdered pigments in the bottom of the letters in the form to get the desired results. And yes, there should be metal inside the concrete. It's called rebar (reinforcement bar) and should be in the form of a three dimensional grid (or two dimensional, for a thin sign). You might also want some heavy duty hooks, attached to the rebar, sticking out of the back of the sign, for easy handling. You will likely need to let it set for several rain-free days (cover it with a tarp, being sure to keep the tarp from touching the concrete, if rain is expected). If you are new to this, I'd expect to take several tries to get it right. (Although, if only the coloring is bad, you could opt to paint it to cover the imperfections. Beware that the paint won't last as long, though, requiring a repaint every few years.) StuRat (talk) 11:38, 13 June 2008 (UTC)

A couple other comments. Don't use water-based pigments and avoid concrete mixes which have loose chunks of metal in them. The pigments will run and the iron will rust and look horrid. In case you don't already know this: you need to pour the concrete right after mixing, so be ready to do so. StuRat (talk) 12:08, 13 June 2008 (UTC)

Make sure the sign is stable (not top heavy) so that if the base settles unevenly, or if someone pushes it it cannot fall over and crush someone. Children have been killed by old tombstones falling over. If you mold it flat, calculate how much it will weign and plan to have a way of lifting it. It could wind up being very heavy. Concrete often leaves voids when poured: sometimes a vibrating device it used to get it to fill in all the areas. Concrete mix (with gravel) is generally stronger, but sand mix would be needed to fill in fine details. The form has to be lubricated. Edison (talk) 13:15, 13 June 2008 (UTC)

And practice several times on smaller scales before going for the final job. 200.127.59.151 (talk) 14:13, 13 June 2008 (UTC)

Black hole confusion

I'm a little confused about what happens to you when you fall into a black hole. My understanding is that an outside observer sees a object take an infinite amount of time to cross the event horizon as the time dilation goes to infinity. An observer falling into the black hole sees itself take a finite amount of time to reach the singularity. My questions are: Does this effect apply to photons, and other objects without rest mass? If an outside observer never sees anything cross the event horizon, how can the black hole ever gain mass? On a related note, what happens when two black holes have overlapping event horizons? Does a region of "safe" space form between them? Outstairs (talk) 06:17, 13 June 2008 (UTC)

Your understand is correct. Photons falling into the black hole can't be observed from outside it, since the photons have to hit your eye for you to see them, photons emitted from an object falling into the black hole will be redshifted, and the redshift will tend towards infinity as the object approaches the event horizon (in the same way time dilation tends to infinity). To be honest, I'm not entirely sure how the time dilation thing fits with the black hole gain mass - I suspect that, from the point of view of the outside observer, the black hole's mass is whatever it was when it formed, but the mass of the accretion disk increases, so the mass of the whole thing is what it ought to be. From the point of view of the person falling into the black hole, it's all perfectly normal. The way two black holes interact (especially when merging) is an area of active research, and I know very little about it. Even if there was a region that wasn't causally disconnected from the rest of the universe (ie. you can leave it), the tidal forces would be enormous, so it still wouldn't be "safe". --Tango (talk) 12:54, 13 June 2008 (UTC)

There are a couple of things stopping a person from even getting close to the event horizon. The event horizon is surrounded by a very hot accretion disk. These disks are usually much hotter than the sun. The size of the accretion disk also tends to dwarf the event horizon, even if the event horizon is enormous as is the case with super massive black holes, the accretion disk is still much bigger. There's also a tremendous amount of radiation. So the heat, combined with the radiation make it impossible for a guy in a spacesuit to ever come close to an event horizon unless he's invincible. Both of these come into effect before tidal forces are present btw. ScienceApe (talk) 16:38, 13 June 2008 (UTC)

The accretion disk is, as the name suggests, pretty flat, so if you approached the black hole from one of the "poles", you would stand a better chance (unless there's a jet coming out of the pole, of course, which I believe there is in cases). If you pick an old enough (isolated) black hole that has already sucked in its accretion disk so that it's all extremely close to the event horizon (from the perspective of an outside observer), all the radiation from it will be redshifted to harmless levels. --Tango (talk) 19:19, 13 June 2008 (UTC)

Like you said, there would still be polar jets. I don't think we know of any black holes without accretion disks. The accretion disk is primarily how we detect them in the first place. It is actually possible to orbit a black hole indefinitely, without ever being sucked in. I don't see why this wouldn't apply to some of the matter in an accretion disk, especially considering the size of the disk, which can extend very far out. I should really emphasize the size of these accretion disks. If you were to look at a black hole from a safe distance, you probably wouldn't even see the event horizon, because it would be dwarfed by the much larger accretion disk. It's THAT big. ScienceApe (talk) 20:00, 13 June 2008 (UTC)

From the point of view of the matter in the disk, it will get sucked in eventually, from the point of view of an external observer, it won't, since nothing can. I'm not sure what your point was, though... As far as I know, you can have black holes without accretion disks, we just can't detect them. You put a large star in an isolated region of space, let it go supernova and the core collapse into a black hole, that black hole will then pull all the rest of the matter star (except for anything that escapes) in towards it and eventually there will be none left that is far enough from the event horizon to be observable from the outside universe (it will still be there, just extremely redshifted). --Tango (talk) 20:15, 13 June 2008 (UTC)

Hypothetically I guess there can be black holes without accretion disks. Thing is, as long as the matter around a black hole sustains orbital speed, it won't fall in. It will revolve around the black hole indefinitely. So in practice, there will always be an accretion disk around the black hole. ScienceApe (talk) 22:51, 13 June 2008 (UTC)

If it's not falling in, it will be cold, so there's no need to worry about it. If it's radiating heat, then it's losing energy and falling in. --Tango (talk) 22:58, 13 June 2008 (UTC)

Not at all, the accretion disk is hot because of friction. The matter is colliding with each other. It can still be hot and maintaining orbit. ScienceApe (talk) 02:27, 14 June 2008 (UTC)

The energy has to come from somewhere. When the bits of the disk rub together, their kinetic energy is turned into heat energy and then radiated as photons. If it's emitting radiation, it must be losing energy, and therefore spiralling down. (Obviously, it can radiate energy because of heat it had before it entered the disk, but that's a negligible consideration.) --Tango (talk) 15:42, 14 June 2008 (UTC)

Point taken. But like I said before, if the black hole has an accretion disk, then you can't approach the event horizon without dying. ScienceApe (talk) 18:31, 14 June 2008 (UTC)

This has been asked many times on the reference desk before. One of the best answers is in this thread. SpinningSpark 22:33, 13 June 2008 (UTC)

earth's magnetism

does earth have null points[since it behaves like a magnet]? if so where are they? —Preceding unsigned comment added by 59.92.248.129 (talk) 08:11, 13 June 2008 (UTC)

There are certainly "imperfections" in Earth's magnetic field, but I'm not sure your "null points" terminology is in standard use. The simplest model is a dipole or offset dipole (i.e. assuming the earth's magnetic field is a "bar magnet" centered at either the exact center of the planet or somewhere else to better fit measured data). Beyond this, you may want to read on the International Geomagnetic Reference Field model: here's a page from NOAA describing it in detail. You may also be interested in the South Atlantic Anomaly; theories to explain this geomagnetic feature vary wildly. Nimur (talk) 10:57, 13 June 2008 (UTC)

See Earth's magnetic field. There is a measurable magnetic field everywhere, though there are low strength fields around the south Atlantic. -- kainaw™ 11:24, 13 June 2008 (UTC)

Also, the Earth's magnetic field isn't constant. When it's about to invert it becomes quite sporadic, with null points and points with the reverse of the expected field all over the place. StuRat (talk) 11:26, 13 June 2008 (UTC)

How can I know if a telephone is also touch tone?

Are all cell phones also touch tones? —Preceding unsigned comment added by 80.58.205.37 (talk) 12:03, 13 June 2008 (UTC)

I don't think that term really applies, since they likely don't send the phone number as an audio signal at all (either as tones or clicks), but as a digital code, instead. However, after you connect to your party, I'd expect to be able to send audio touch tones so you can navigate phone message systems. For example: "Your call is important to us, although obviously not important enough to actually answer ... Press 1 if, for some strange reason, you speak English". StuRat (talk) 12:16, 13 June 2008 (UTC)

I think you mean "Press 1 if, unlike us, you speak English." :-) --Anon, 22:20 UTC, June 13, 2008.

(Edit conflict) Cell phones transmit their dialing information to the network digitally. But once a call is established, they'll generally emulate a Touch Tone phone and transmit the cirrect audio boops and beeps so that automated call response systems work as you'd expect. So yes, in the way that you probably care about this, they are all "Touch Tone".

Atlant (talk) 12:24, 13 June 2008 (UTC)

Actually, in many cases, cell phones work better with automated systems that are expecting analogue DTMF tones. A lot of modern POTS (analogue phones) output the DTMF tone for a short burst of predetermined duration. This can cause problems, especially on noisy lines, because the server at the other end had insufficient time to decode the tone. This is not generally such a problem with older models which will carry on outputting the tone for as long as you hold your finger on the button; so the human can compensate for the bad connection by putting out longer bursts. Cell phones also (most models anyway) tend to follow the old scheme of "tone while button down". Not sure why this is, possibly because cell phones by there nature have greater problems maintaining a good connection and the sesigners are trying to compensate. SpinningSpark 22:19, 13 June 2008 (UTC)

raccoons

I live in an area near a river where raccoons come into the neighborhood looking for dog and cat food or kittens or whatever else they can find to eat. Whenever someone leaves a bucket or other container out and it fills with rain water they make a habit of pooping in it. What might be the reason for this behavior? -- Taxa (talk) 13:06, 13 June 2008 (UTC)

Raccoons are not dumb. They know that standing feces can cause a lot of health problems. So, the defecate in water to keep it away from where they may step. If no water is available, all raccoons in a group will tend to defecate in the same spot to keep it localized. This is not unique to raccoons. Non-domesticated animals try to be clean. Even my hedgehogs will go in a litter box to keep their area clean. This came up on Futurama:

Fry: Psst! Leela! You've got to get me out of here! It's horrible! Eating scraps; letting my waste drop wherever it falls, like an animal in a zoo!

Leela: Animals go in the corner.

Fry: The corner! Why didn't I think of that?

-- kainaw™ 14:39, 13 June 2008 (UTC)

Come now. Just because an animal is "not dumb" doesn't mean it has sufficient capability for abstract thought to know that some practice "can cause a lot of health problems". Much more likely we are talking about instinctive behavior, or behavior taught in infancy, resulting from natural selection. (I use the term broadly here, not limited to genetically determined traits as that article applies. In other words, it could be that raccoons that learned to do this live longer and have children that observe them doing it and copy it.) --Anonymous, 22:28 UTC, June 13, 2008.

I don't think that what you're are seeing in the water is their "poop." Normally raccoons have communal defecation sites (latrines), often at the base of trees or on flat elevated surfaces. It is true that containers of water accessible to raccoons look as if they have been defecated into. However, what you are most likely seeing is the dirt and other foreign materials that result from their habit of "washing" or "dousing" their food in water. They do not always put their food in water before eating it, and there seems to be no concensus as to the function of this behavior. Take a look at these links with regard to where racoon "latrines" are located.[30] [31]--Eriastrum (talk) 21:20, 14 June 2008 (UTC)

Shovel-Shaped Incisors

Why do Asians (mongoloids) have shovel-shaped incisors? A friend of mine says it is because they evolved to subsist on a diet that contained less meat and more vegetables.

Are there any other modern animal species, besides humans, that have shovel-shaped incisors? 71.231.122.22 (talk) 13:26, 13 June 2008 (UTC)

Your friend has the cause and effect of evolution backwards. Animals do not evolve to serve a purpose. They purposely attempt to fill a niche in the environment and evolve to better fill that niche. So, your friend is actually claiming that the Asians found more vegetables than meat and attempted to fill the primarily vegetarian niche in their area and, as a result, evolved shovel-shaped incisors to better fill that niche. A quick scan of medical studies on this topic shows that it was suggested that this evolutionary trait was a result of a vegetarian diet. However, most studies refute that claim and leave the trait to a pure chance mutation. Otherwise, it would be reasonable that more vegetarian-based cultures would develop the same trait. -- kainaw™ 14:31, 13 June 2008 (UTC)

See genetic drift. ScienceApe (talk) 16:44, 13 June 2008 (UTC)

BTW, quite a large number of Asians are not mongoloids Nil Einne (talk)`

Big red ant!

I just flushed a large red ant from my apartment. I've been having an ant problem, but, so far, they've all been the usual small black ants. This is the only one I've (ever) seen like this. It was nearly an inch long and a light/bright red color all over. It had no wings (thankfully). When I first saw it, it was so large, I didn't expect it to be an ant, but up close that's certainly what it seemed to be. Unfortunately, I don't have any pictures to show.

Naturally, I was wondering if anyone here might know what it was. I live just outside Washington, DC, in a heavily wooded area (Takoma Park, MD). Or, maybe someone could point me to a list of local species?

Thanks! — 68.49.3.251 (talk) 15:24, 13 June 2008 (UTC)

It's swarming time and you probably encountered a queen who has shed her wings.

Atlant (talk) 16:03, 13 June 2008 (UTC)

Perhaps it was a Mutillidae? (Although not an ant, they do appear as one.) Ζρς ι'β' ^¡hábleme! 19:14, 13 June 2008 (UTC)

Is Dorylus fulvus found in the US (as an invasive species, that is)? The males a.k.a. drones a.k.a. "sausage flies" are by far the largest ants I've ever seen. They are up to an inch long and brownish-red, definitely matching what you say. They have wings when they fly, but AFAIK the workers chew the males' wings off as soon as the males land nearby. There are pics of Dorylus drones on the net. Is that close to what you saw?! I've never heard of Dorylus in the US, but if it is one, I'd be concerned. --Dr Dima (talk) 22:07, 13 June 2008 (UTC)

fruit contamination

Is it possible for bacteria to enter intact fruit through the root system? —Preceding unsigned comment added by 1022wcharles (talk • contribs) 20:44, 13 June 2008 (UTC)

Biology isn't my area, but Plant disease#Bacteria might give you some useful information while you wait for an expert. --Tango (talk) 20:54, 13 June 2008 (UTC)

I would think it would be possible, but unlikely. Bacteria entering through intact roots would be like bacteria entering your body through intact skin. It's possible, but first the bacteria would have to set up a colony on the surface and sufficiently damage the surface so that it could gain entry. StuRat (talk) 23:27, 13 June 2008 (UTC)

water pressure

If I had a column of water 1 millimeter in diameter and 1 mile tall, would the pressure at the bottom of the column be the same as the pressure at the bottom of a column 1 mile in diameter and 1 mile tall? Nadando (talk) 21:03, 13 June 2008 (UTC)

That's correct. The volume of water in the container isn't what creates pressure at any point inside the volume; it's the height of the volume above the measurement point that matters. Imagine dipping a 1-mile hollow tube, open at both ends vertically into the ocean. The pressure inside the bottom end of the tube will still be the same as the pressure outside the bottom end of the tube.

However, when you get down to a really small-diameter container (less than the 1mm in your example), friction and capillary action are the dominant forces, not gravity. Make the diameter small enough, and water can simply stick to the sides, completely filling the container, no matter how tall it is. ~Amatulić (talk) 21:10, 13 June 2008 (UTC)

Presumably that means there is significantly less pressure in a capillary? So the answer to

the OPs question would then be no, its different? SpinningSpark 21:57, 13 June 2008 (UTC)

Amatulic said a capillary was narrowing than 1mm, which would mean in the OP's case, they would be equal. --Tango (talk) 22:27, 13 June 2008 (UTC)

Its not exactly an on/off effect. It just diminishes with increasing diameter according to inverse R which you can see in the article. So there is still a noticeable effect (the article says 0.5mm will lift 2.8mm of water) at 1mm. The effect on pressure is going to be small but it must happen surely?, otherwise the water would not rise. SpinningSpark 01:01, 14 June 2008 (UTC)

On June 29, 1973, in Philadelphia, a task for liquefied natural gas was under construction. Its main structure was 85 feet high (25 m) and consisted of a 5/16 inch (8 mm) steel liner surrounded by an 8-inch (20 cm) prestressed concrete wall. The space between the steel and the concrete,as built, was only 1/100 inch (0.25 mm) thick -- but when water accidentally got into it, the pressure at the bottom was enough to push the concrete out of position. Of course, this then widened the gap and more water got in and the concrete continued to shift. (Source: Design and Construction Failures: Lessons from Forensic Investigations by Dov Kaminetzky, published 1991 by McGraw-Hill, ISBN 0-07-033565-6. More precisely, my source is notes taken when I had that book out of the library.) --Anonymous, edited 22:49 UTC, June 13, 2008.

Addicted to you

Hello smart wikipeoples. Could all psychological addictions (i.e. those lacking the presence of psychoactive substances) be considered addictions to dopamine (and certain endorphins)? Thanks in advance, Kreachure (talk) 22:44, 13 June 2008 (UTC)

What's wrong? Too dumb? Too hard? Makes no sense? Please, say something about it! (This is the only unanswered question right now in the desk, and it's been so for almost a day!) Kreachure (talk) 20:25, 14 June 2008 (UTC)

Patience is a virtue, right? I don't really know much about the topic but for example say if you were addicted to sex then the only thing involved in 'how you feel' is endorphins, so yes, it could be assumed that the addiction was to endorphins as that provides the feeling. Regards, CycloneNimrod ^talk?_contribs? 20:56, 14 June 2008 (UTC)

The Wikipedia article for addiction states in the first line: "Addiction is a state in which the body relies on a substance for normal functioning". Considering that all humans and many other species are reliant on dopamine/endorphins you could say they are all addicted.

What I'm guessing instead is that your argument has spawned from something like: "Bob has sex a lot. Bob says he is addicted to endorphins". Apart from the issue that sex doesn't just involve endorphin release (i.e. oxytocin), you have to realise that animals strive for homeostasis, and behaviour such as addictions can be seen as decisions made as a result of calculations by the brain, in order to maintain homeostasis. --Mark PEA (talk) 23:12, 14 June 2008 (UTC)

Hmm, I'd rather consider addictions of any kind to be behavior against homeostasis, since your body goes out of control all over from an excessive yearning for substances it doesn't really need... which could lead to a total system imbalance and breakdown, in fact. Kreachure (talk) 23:49, 14 June 2008 (UTC)

June 14

Flood stage and topographic maps:Cedar Falls,Iowa: A question touching on the sciences of mapping and hydrology.

In the recent flood news in Iowa, I am left confused by the lack of relation between the river being "so many feet above flood stage" and how that relates to topographic maps showing only how many feet above sea level various parts of a town are."Flood stage" is an arbitrarily river level at which it "starts to do damage" and cannot readily be determined from a toporaphic map. For instance, in Cedar Falls, Iowa, how many feet above sea level is "flood stage?" A USGS topo map, 7.5 minute, downloadable at [32] shows the river normally at about 841 feet above sea level, and the first contour lines shown near the riverbank are 850 feet, but how is one to know if the water getting there "starts to do damage" or just makes some mud a bit wetter? On the other hand some structures seem to be below the 850 contour, basically at the normal river level. Where is a tabulation of "flood stages" for various cities in relation to elevation above sea level? Where are maps showing the 100 year and 500 year flood plains for that city?(or other cities in general)? Also, some news stories give the river level in "gauge" relative to some arbitrary historic measurement point. Where is a listing of "gauge" levels relative to actual elevation? Edison (talk) 00:13, 14 June 2008 (UTC)

I finally tracked dow a site [33]relating "gage" and "flood stage" to topographic map elevation for this town, but I still would like a general source for 100 year/500 year flood maps for various U.S. locations. Thanks. Edison (talk) 00:39, 14 June 2008 (UTC)

Ants native to the South Pole

Are there any ants native to the South Pole? 122.107.192.10 (talk) 06:41, 14 June 2008 (UTC)

There is no life native to the South Pole. Antarctica, couldn't say. ~~ N (t/c) 07:42, 14 June 2008 (UTC)

I'm relatively sure that there are no ants at either of the poles, it's simply too cold. If you mean the southern hemisphere, i'm sure someone can help you. Regards, CycloneNimrod ^talk?_contribs? 07:50, 14 June 2008 (UTC)

According to our article on ants, ants are native to all continents in the world except Antarctica. (see subsection here). So, the short answer would be no, there are no ants native to the South Pole or Antarctica. Eric (EWS23) 08:28, 14 June 2008 (UTC)

Ants, being insects, are cold-blooded. All cold blooded insects need a warm enough environment to keep them from freezing solid. Some insects do have the ability to freeze and then thaw when the temp warms up, but the temp never warms up enough to thaw an ant at the South Pole. Also, there would be nothing for the ants to eat at the South Pole, as nothing else (plants or animals) can live at those temps for long. StuRat (talk) 14:21, 14 June 2008 (UTC)

No ants in antarctica? Edison (talk) 20:00, 14 June 2008 (UTC)

It was too cold for them so they all "said uncle", and left. StuRat (talk) 02:05, 15 June 2008 (UTC)

Biology

Please Suggest some topics for class 12 to do a project on biology. —Preceding unsigned comment added by 218.248.70.235 (talk) 09:42, 14 June 2008 (UTC)

I presume that you are not the teacher and this is homework, which you should do yourself. But to help you out, take a look at Portal:Biology, taht might give you a few ideas. SpinningSpark 09:51, 14 June 2008 (UTC)

Autism

Does autism affect the age that one lives to? Interactive Fiction Expert/Talk to me 10:40, 14 June 2008 (UTC)

No, not much and not directly. It can affect how one lives their life and make certain causes of death more likely because of their choices but as a disease it will not kill you. Regards, CycloneNimrod ^talk?_contribs? 11:43, 14 June 2008 (UTC)

Question on atomic structure

Hi! I'm a grade 10 high school student and this has been a doubt that has been persisting for long...... In Bohr's model of the atom, he says that the electron doesn't lose energy as long as it's revolving in the same orbit. But why?? why doesn't it lose energy? I've had people explaining it as, because of centrifugal force, but in one of my textbooks, I read that Rutherford proposed the same thing in his model of the atom; but he was later proved wrong, as "according to electrodynamics", to quote from the book, "a charged particle revolving around an oppositely charged particle should lose energy and its radius should decrease, ultimately causing the electron to collapse into the nucleus. As this does not happen in the case of an atom, Rutherford's model failed to explain the stability of the atom". I know Bohr made a major advance, where models of atoms are concerned, with the quantization of energy concept,but I still don't understand how the electron could keep accelerating(by change of direction) along a circular path without losing energy...........can anyone tell me how he explained it? none of the books I have gave a satisfactory explanation on that part. Surely he must have had a good explanation for that statement?? 116.68.76.47 (talk) 11:17, 14 June 2008 (UTC)A 15-year old

The Bohr model is actually a very primitive model and not representative of the real situation. You are probably taught this model in school because it is easy to explain and understand, however it is a very simple view and is fundamentally incorrect. In reality, the electron does not actually orbit the nucleus at all, in the way described by the Bohr model. We move onto the more complex valence shell model of the atom. In this model, the electron is not considered a particle and instead exhibits wavelike behaviour, see Wave–particle duality. The electron may exist in a particular region, or spatial distribution, around the nucleus. The shape of this region is dependant upon the particular quantum state of the electron. This region is called an orbital but this may be mis-leading, since due to the wierdness of quantum mechanics, the electron may exist in all regions of the orbital simultaneously. I hope this helps in your understanding and I commend you for asking such a question, it only goes to show that you shouldn't believe everything you are taught in school. Jdrewitt (talk) 11:35, 14 June 2008 (UTC)

If the electron is moving in a path of constant electric field potential (ie in a spherical shell at constant distance (radius) from the proton(s) ) ... and E(total) = E(kinetic) + E(potential).. E(total) cannot change.. so...87.102.86.73 (talk) 11:36, 14 June 2008 (UTC)

No, any charged particle undergoing a circular trajectory will emit electromagnetic radiation, see cyclotron radiation. So the Bohr model, although nicely introducing quantised energy states etc, doesn't get around the fact that the electron will eventually lose its kinetic energy and the electron will fall into the nucleus. The only way to overcome this problem is to introduce the electronic probabilty distribution valence shell model as described by quantum mechanics. Jdrewitt (talk) 12:05, 14 June 2008 (UTC)

Bohr feigned no hypothesis regarding the reason for the fixed orbitals. His only justification was that it led to correct predictions, which was also Newton's only justification for his inverse-square law of gravity. But Bohr's model, unlike Newton's, turned out to be wrong in almost every respect. In a real (unexcited) hydrogen atom, the electron essentially does fall into the nucleus. See my comment in this thread. Of course, my explanation appeals to the uncertainty principle, about which we also feign no hypothesis. -- BenRG (talk) 22:18, 14 June 2008 (UTC)

Eutanasia

• This question has been removed as it may be a request for medical advice. Wikipedia does not give medical advice because there is no guarantee that our advice would be accurate or relate to you and your symptoms. We simply cannot be an alternative to visiting the appropriate health professional, so we implore you to try them instead. If this is not a request for medical advice, please explain what you meant to ask, either here or at the talk page discussion (if a link was provided). Regards, CycloneNimrod ^talk?_contribs? 12:03, 14 June 2008 (UTC)

I don't see anything in the deleted question that's a request for medical advice. The question asks for names of hospitals that provide certain services in a certain locale. This is the type of information that a dentist referral service would provide. --71.162.233.228 (talk) 14:49, 14 June 2008 (UTC)

Agreed. Doesn't look like medical advice to me. I'll talk to Cyclonemim on his/her talk page. --Tango (talk) 15:31, 14 June 2008 (UTC)

Perhaps you're right, i'm not really sure, I kind of saw euthanasia and a request and, wrongly, assumed. Feel free to restore it. Apologies! Regards, CycloneNimrod ^talk?_contribs? 16:32, 14 June 2008 (UTC)

The question was:

In what hospitals of Belgium the procedure of eutanasia is made for woman`s been ill for some years. She in the terminal state. No :treatment is of help.

Help,please !

///,,,... —Preceding unsigned comment added by 92.47.113.132 (talk) 11:49, 14 June 2008 (UTC)

Anyone know the answer? --Tango (talk) 17:38, 14 June 2008 (UTC)

From this it sounds as though euthanasia is pretty tightly regulated in Belgium. Given tight regulation and a progressive health-care system like Belgium's, it would seem reasonable for the patient to make the request of her physician, in accord with the regulation referred to in the article I cited. Sounds as though they'd have to assess appropriateness (the law apparently requires "constant and unbearable physical or psychological pain" among other things) and then if appropriate either assist or refer to the proper specialist. Sorry I don't have a more direct answer. Scray (talk) 19:31, 14 June 2008 (UTC)

Ununoctium

Can anyone tell me why, according to it's article, Ununoctium is expected to have a tetrahedral shape in a molecule with fluorine, whereas the other noble gases have planar shaped molecules? Regards, CycloneNimrod ^talk?_contribs? 14:32, 14 June 2008 (UTC)

The article tells you (read the "Properties" and "Compounds and uses" sections of the Ununoctium article) and provides cites to explain further the principles and the actual full details of the calculations leading to this conclusion. DMacks (talk) 18:20, 14 June 2008 (UTC)

bread mold causing dancing

i heard a rumor that sounds fake (i would be shocked if it were true)
its that there was a town during the medieval period that danced for hours and it was due to a mold in their bread that was caused by them not cleaning their grain and apparently (this is where the story goes from bad to worse) the type of mold refered to is used in the production of the drug "acid"
so am i wrong?
is this true?

See the article Ergotism. Ergotamine, the principal alkaloid produced by the ergot fungus, is, in fact, closely related to LSD. Deor (talk) 16:00, 14 June 2008 (UTC)

Growth rings versus Wood grain

The question here: [34]: what is the distinction (if there is one) between Growth rings and Wood grain. Answers on Talk:Wood grain please. Thank you. --VanBurenen (talk) 20:36, 14 June 2008 (UTC)

Growth rings are the circles seen in a cross-section of a log. Grain is the pattern seen running longitudinaly down the length of a sawn log. SpinningSpark 23:59, 14 June 2008 (UTC)

That's right, they are really growth cylinders. If you cut them across, you get circles, if you cut them lengthwise, you get lines. If you cut them at an angle, you can even get growth ellipses. StuRat (talk) 00:11, 15 June 2008 (UTC)

I agree with the descriptions of growth rings, but isn't grain whatever pattern one sees in a cut surface of wood (cross-sectional or longitudinal)? Scray (talk) 00:44, 15 June 2008 (UTC)

Well, the grain does come from the growth rings. There are variations in the rings where branches join the trunk, where there is a knot, or damage from insects, disease, storms, or human activity. All this will also affect the grain produced when the wood is cut in the opposite direction. StuRat (talk) 02:03, 15 June 2008 (UTC)

Polyphenylethene residues

I recently dissolved a large quantity of expanded polystyrene in propanone. As I understand it, this involves the structure of the polyphenylethene changing so that the polymer molecules are more densely packed.

However, after the reaction, there was left a beige residue. I removed this from the vessel and it was extremely sticky, like melting plastic. From the articles on polystyrene and propanone, I can't work out what this was: phenylethene is a liquid at room temperature and polyphenylethene a brittle solid. Perhaps this is an oxide?

Hopefully I am missing something obvious. Thanks very much in advance for your help!

86.149.177.103 (talk) 22:59, 14 June 2008 (UTC)