Talk:Coriolis force/Archive 1

"there is no real force acting on the object"... 'k, gotta explain something to me.

Any time a body's world line deviates from a straight line in whatever coordinate system one's using, a force has to be concocted to account for that. If we're fool enough to use polar coordinates, we have to come up with Coriolis forces. If we're fool enough to use a rotating coordinate system, we need to invent centrifugal forces.

But didn't general relativity do the same thing to gravity? Isn't, in fact, any "force" that operates in strict proportion to the mass of the affected body, imaginary - an acceleration term that can be eliminated by an appropriate change of coordinates?

Aren't Coriolis and gravity equally imaginary?

(William M. Connolley 20:26, 21 Feb 2004 (UTC)) I essentially agree with the above... Coriolis force appears as a result of co-ordinate transform. Gravity is equivalent to acceleration. OTOH, Coriolis does no work (being dead. Sorry, no, I mean: being orthogonal to the velocity) - could this be a criterion for it being "imaginary"? Or is that an arbitrary test? I notice several google-found web pages hedge their bets by describing Coriolis as imaginary, but putting imaginary in quotes to weaken it.

Section: is coriolis "fictitious"?

I've added a section to the page about the above. I'm not 100% sure about this - anyone who really knows general relativity (or coriolis) may care to correct.

To make things consistent, I've also cut some text from the article.

A minor point: I cut "(due to Newton's laws of motion)" - I don't think this is right even if coriolis is fictitious - its a kinematic effect.

Your description of GR is pretty accurate except for the bit about gravity not being a pseudo-force. In the context of GR, it certainly is. By the same token, the Coriolis effect should certainly be understood as a pseudo-force, in that it does not occur in inertial frames. -- Xerxes 20:58, 2004 Jul 26 (UTC)

(William M. Connolley 21:07, 26 Jul 2004 (UTC)) I think that might depend on what you mean by a force. But if you are saying that Coriolis is no more fictitious than gravity, that will do, since "everyone" knows that gravity is not fictitious...

[Owen Jones] 11:22 GMT+1 24 Sep 2004. I think all the talk of General Relativity (GR) is beside the point. In classical mechanics fictitious forces arise as a result of moving from an inertial frame to a non-inertial one, ie from the fixed frame of the stars to the rotating frame of the earth. With the advent of relativity we have moved from having one privileged set of non-inertial frames to every frame being equal, and this does complicate matters. The last section is correct, but I feel it should explain that fictitious is being used in a mathematical sense. One could almost read it and get the impression that it is wrong to call the coriolis force a fictitious force. In the wider scheme of things, perhaps we could do a page on mathematical appropriation of everyday terms to describe mathematical concepts. For starters there are differentiation and integration. What is so normal about a normal group? What is so irrational about irrational numbers? What is so fictitious about fictitious forces?

(William M. Connolley 18:31, 24 Sep 2004 (UTC)) Well, in wiki we can do "fictitious (natural language)" and "fictitious (precise)" but you can't do that in speech. But on the cor page, I'm not at all sure we are distinguishing the two meanings or need to. I wrote that bit: I'm happy to be corrected: but as far as I can see there is no physical reason to call coriolis forces fictitious. Thus the word is used in a maths and physics sense. I think it *is* wrong to call cor fictitious. As far as I can see, GR renders the distinction meaningless.

As to irrational numbers: thats a softball: they are irrational because they are not ratios (nothing to do with rational (mental state)). Perhaps you mean imaginary numbers? :-)

In fact there is one sense in which cor is imaginary: it does no work. But... who says that is the test?

(Owen Jones 21:59, Sep 26, 2004 (UTC)) I used to be a big fan of QM and GR as far superior to classical phsyics. But then I realised that for all but the most extreme problems (large velocity, large mass or small scale) classical physics is the rational choice. Also, the majority of people actually think in terms of classical mechanics (when you take a sharp corner in a car you feel a force), so I think it is fair to have it in wikipedia. I think it's important point that this isn't actually a force (I can't think how I would define a force, but for one there is no equal and opposite reaction force anywhere). I would favour something along the lines of

In physics the term 'fictitious force' is used when what appears to be a force is caused by being in an accelerating frame of reference. For example, the force you feel when taking a tight corner in a car is a fictitious force in this sense. This is not to say that the force is imaginary in any sense.

(William M. Connolley 22:12, 26 Sep 2004 (UTC)) But what is an accelerating frame of reference?

(Owen Jones 20:09, Sep 27, 2004 (UTC)) One that is accelerating with respect to the fixed frame of the stars is how it was originally defined.

I am very new to Wikipedia, so do tell me if I should just get on with it and edit the page myself, instead of discussing it here first.

(William M. Connolley 22:12, 26 Sep 2004 (UTC)) Its very much up to you. But if something is a subject already discussed, talking on the talk page is usually a good idea. If (elsewhere) no one responds then just do it.

I don't quite follow: are you saying that it is wrong to call the coriolis force fictitious in a maths and physics sense because we should use GR instead of classical mechanics and in GR there are no fictitious forces because no frame is privileged as being the rest frame?

(William M. Connolley 22:12, 26 Sep 2004 (UTC)) Yes, except that "use GR" isn't meaningful. You can't just pick-and-choose your theory (well not if you really want to know what is going on). GR is the best theory going.

(Owen Jones 20:09, Sep 27, 2004 (UTC)) If you want to compute where a projectile that is fired vertically up from the surface of the earth will land, then you apply classical dynamics (which I think ends up using the coriolis effect). When I say 'use GR' or 'use CD' I mean apply that theory to obtain an answer. You could use GR to get an answer to this problem, but it would be much harder and would give almost the same answer as CD, precisely because CD is a very good approximation to GR. There are situations where you have to use GR to get an answer which tallies with observations, but you only meet them in very specialised situations.

As for irrational numbers, I know that there is a logical argument for why rational and irrational are used as they are, but when people say 'rational' they don't mean 'in ratio' they mean 'in reason', so although maths may not have appropriated the word it does use it in a different sense and can easily be misinterpreted.

(William M. Connolley 22:12, 26 Sep 2004 (UTC)) In maths, 'rational numbers' means 'in ratio'. Yes the word has other meanings in natural language, but so what?

(Owen Jones 20:09, Sep 27, 2004 (UTC)) What I was proposing was a page to explain some of the confusing terms used in maths. Just because 'rational' has a sensible explanation doesn't stop it from being confusing when first encountered. I admit phrases such as 'fictitious forces' are more confusing and really could have been chosen better.

I've decided to remove my comments from this page.

after reading this comment

>>>since radians are dimensionless. <<<

I decided you here need much more help than I can provide. I hoped to clarify things but instead can see it will just start argument.

Sorry for the inconvenience.

Please remove all record of my correspondence. I retract the material I presented and retain all copyright privileges and you or your group retains none.

When you posted, you agreed to license your edits under the conditions at Wikipedia:Copyrights, which include the proviso that "you can never retract the GFDL license for the versions you placed here"... Marnanel 04:06, Apr 5, 2004 (UTC)

Indeed. And since radians *are* dimensionless, its clear who needs the help... though I'm not sure where you found the comment you refer to.

I suppose degrees, gradients, and percent slope, are dimensionless too! :rolleyes

(William M. Connolley 08:41, 2004 Apr 6 (UTC)) See: angle

2 px

I put two pictures in to illustrate two phenomena: atmospheric circulation causing prevailing winds, and rotation of storms. --wwoods 16:54, 8 Apr 2004 (UTC)

(William M. Connolley 17:24, 2004 Apr 8 (UTC)) Yes but... I don't much like the prevailing winds pic, its quite misleading as a pic of the actual circulation. Sometime I'm going to write the ferrel cell does not exist and I'll be in a stronger position then :-) Put it back if you must...

I'm not wedded to that picture, which I found on atmospheric circulation, but it seems like a reasonable subject for a picture. Can you find/make a better one? -wwoods 17:38, 8 Apr 2004 (UTC)

(William M. Connolley 18:40, 2004 Apr 8 (UTC)) That will be part of the ferrel cell page... I have a project for dynamically correct meteorology on wikipedia. But, its liable to be a slow process. Perhaps I'm being too picky. http://www.antarctica.ac.uk/met/wmc/circ.png might be a better picture... it shows the zonal mean meridional wind (admittedly from a climate model, not observations, but its a good climate model...). Or http://www.antarctica.ac.uk/met/wmc/circ1.png. See how much stronger the hadley cell is than the others... hmm, but it may not be a very good general-purpose pic.

Dimensions stuff that doesn't belong here

From the angle link " Note that angles are dimensionless, since they are defined as the ratio of lengths. " So how do the dimensions of R, theta and Phi in spherical coordinates aspire to the claim of being a dimension? Or are two of those a half ratio of the third???

(William M. Connolley 08:25, 2004 Apr 15 (UTC)) You're confusing "dimensionless" with "dimension".

Since the angle can be determined by dividing the arc length by the radius doesn't mean they are defined that way,

(William M. Connolley 08:25, 2004 Apr 15 (UTC)) but it does mean they *can* be defined that way, and that any other way must be consistent with that, and that therefore angles are dimensionless.

and it certainly doesn't mean they are dimensionless because the dimension of length is gone. They have now acquire the dimensional units of radians, degrees, or etc depending on which system you use.

However, as I said you need more help here than I can provide.

(William M. Connolley 08:25, 2004 Apr 15 (UTC)) Then why don't you go away and stop being "helpful"?

Bye! I hope you don't get your dimensionless radians confused with your dimensionless degrees. :rolleyes