Talk:Fictitious force/Archive 2

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When is a force doing work?

It is possible to characterise a "fictional force" as those which, in principle, do no work. William M. Connolley 13.06 5 Nov 2004 (UTC))

Here's a physicist's point of view:
Imagine the following setup: a beam of charged particles is led trough a succession of 8 chambers. In each chamber there is a uniform magnetic field with exactly the right fieldstrength to make the Lorentz force deflect the path of the particles 45 degrees. (Actually that is quite a normal design for a storage ring. Storage rings ar usually polygons, not the smooth circles of schematic drawings) In each chamber work is done, the momentum of the particle is changed. The 8 chambers together form a closed loop, effectively the charged particles are going around in a circle. In a cyclotron, where the motion is perfectly circular the same is valid. The momentum is changing all the time, so the force is doing work all the time.
That is rather spooky, how can a force that is perpendicular all the time do work?

One way of interpreting that is to consider circular motion as a superposition of two linear independent harmonic oscillations. That is valid in mathematics, and stunningly, it appears it applies to actual physics. If you set up a single harmonic oscillation then there is a constant back and forth conversion between kinetic energy and potential energy in that particular direction, and once a kinetic oscillation is set up its direction is conserved. Conservation of direction is a fundamental property of nature. With a single harmonic oscillation it is quite obvious that there is constant conversion of a conserved quantity of energy, and that there is conservation of direction. In circular motion there is also constant conversion, althought that is less obvious. Cleon Teunissen 22:34, 31 Jan 2005 (UTC)

the Feb 2 version of the article.

What a legacy Einstein left us!
In every school physics is first introduced by teaching newtonian physics, and they should. Learning newtonian physics is such a good entry to physics, it teaches thinking physics, without overwhelming, you can't teach basic physics any other way. It's the only way to pave the way for relativistic dynamics. Schools should never skip newtonian dynamics. [...] only particle accelerator physicists and cosmologists use relativistic calculations, that's like point zero zero one percent of the physics community.
So there we are: a science with two current paradigms simultaneously.

Err, don't get me wrong; if particle accelerator physicists wouldn't use relativistic calculations the machines wouldn't work, that proves beyond doubt that Einstein was right.Cleon Teunissen 07:50, 30 Jan 2005 (UTC)

I feel the article should start with discussing in newtonian terms and that it should subsequently move on to relativistic dynamics.
the reader doesn't have to plough through the relativistic stuff, the newtonian discussion is sufficient. The only purpose of the general relativity section is to show that as far as the fictitiousness is concerned general relativity agrees with newtonian dynamics. Cleon Teunissen 07:37, 30 Jan 2005 (UTC)

The importance of inertia

Cleon Teunissen 16:02, 9 Feb 2005 (UTC)
In terrestial kinematics, inertia always manifests itself, and because of that it tends to be overlooked. Newton proposed the following definitions: if two forces balance each other, then there will be no acceleration. If they do not balance, or if there is only one force, then there will be acceleration. These definitions work well, but they tend to relegate inertia to obscurity. Inertia is a force to be reckoned with. But unlike for example friction, inertia cannot prevent motion, nor sustain it. Inertia is not only powerful, it seems, but also quite powerless.

When two objects collide, their inertia and relative velocity determine how much kinetic energy can be converted into damage and heat. There is one reference frame in which all kinetic energy is converted to damage and heat, that is de reference frame that is co-moving with the common center of mass of the two colliding objects. So single objects do not have an intrinsic kinetic energy, but if two objects are considered as a single system, then this system does have a unique amount of kinetic energy.

Gravity accelerates without manifestation of inertia, and that is very odd, for inertia is the universal "currency" of kinetic energy. When two objects are accelerating towards each other under the influence of each others gravity, and they collide, their kinetic energy has been building up, leading up to the collision. How can that be if there was no manifestation of inertia during the acceleration?
I don't quite understand that, but it seems to me that it must be related to the fact that gravity changes the progression of time.

The name 'fictitious force' is ill chosen, because the force involved is real physics; inertia is far from imaginary. It just that inertia cannot prevent acceleration. --Cleon Teunissen 16:02, 9 Feb 2005 (UTC)

Now the stage is set to get an understanding why gravity fits the description of a fictitious force rather well:

(William M. Connolley 17:10, 9 Feb 2005 (UTC)) Now the stage is set to get an understanding why gravity fits the description of a fictitious force rather well... which is a problem, because very few people would agree with you that gravity is fictitious. In some ways, what you have achieved is an a proof-by-contradiction: you have managed to show that your definition of fictitious force is not a good one. I would rather the article began with something like: "the concept of fictitious force is not clearly defined and is of no obvious physical use" and perhaps continued from there.

I shall rephrase that tongue-in-cheekish part of the article in order to avoid the misunderstanding you mention. Gravity fits the discription of fictious force to an extend, but not completely.
I get the impression you have read the article only partly.
(William M. Connolley 17:20, 11 Feb 2005 (UTC)) True. I think its too long.
It says in the article that in the case of for example centrifugal force, releasing grip is the first step to getting out of trouble. After you have released grip (say a helicopter has lifted you from the rotating disk) you stil have a velocity, but that velocity won't increase; and it won't increase in any perspective, from local to universal.
In the case of gravity, releasing grip is the last thing you want to do if you are hanging on to a rope under a helicopter.
But this does not address the deeper issue. Your paradigm is a different one. Your physics paradigm is alien to general relativity.
(William M. Connolley 17:20, 11 Feb 2005 (UTC)) I disagree. But I think yours is...
As is the way with paradigms, all words and expressions have a different meaning in your world. This is making communication very difficult.
Einstein was interested in what formulations are invariant under relativistic transformation,and the phyiscs community has followed his example. In special relativity there is the space-time interval:
(dx)2 + (dy)2 + (dz)2 - c2(dt)2
The space-time interval is invariant under Lorentz transformation, hence it is seen als more fundamental than space and time separetely. --Cleon Teunissen 22:32, 10 Feb 2005 (UTC)


(William M. Connolley 17:10, 9 Feb 2005 (UTC)) I would rather the article began with something like: "the concept of fictitious force is not clearly defined and is of no obvious physical use"

A statement of that sort would be an flagrant contradiction of physics facts.
(William M. Connolley 17:20, 11 Feb 2005 (UTC)) I disagree. I can't think of any physical use for the concept of "fictitious force", or any problem which is simplifies or makes possible. Can you? Does the page provide any?
Manifestation of inertia is definable and it is very important to take account of inertia correctly.
I am in favor of replacing all mention of 'fictitious force' with 'manifestation of inertia'. --Cleon Teunissen 22:32, 10 Feb 2005 (UTC)
I mean: what I am in favor of is that in all future physics textbooks the expression 'fictitious force' is avoided, and that it is called 'manifestation of inertia'. In order to explain why the expression 'fictitious force' was introduced in the first place, an encyclopedia should devote an article to it. --Cleon Teunissen 22:48, 10 Feb 2005 (UTC)

(William M. Connolley 17:20, 11 Feb 2005 (UTC)) You are coming very close to (may have exceeded) the "no original research" guidelines. Wiki is not here for your personal opinions (or mine) but to report what is out there.

The invariance principle of relativistic physics

Cleon Teunissen 11:33, 11 Feb 2005 (UTC)
In relativistic phyisics, expressions that are invariant under transformation are considered the true 'nuts and bolts' of the underlying physics. An example from relativistic dynamics at non-relativistic velocities: when two objects collide, kinetic energy is converted to damage and heat. The amount of kinetic energy that is converted can be calculated in any inertial reference frame, it will allways come out the same: it is an invariant quantity. At relativistic velocities the full relativistic expressions must be used, and they have the same property.

The aim of relativistic physics is to allow observers in different reference frames to agree. Each observer has the full set of transformations at his disposal, so he can transform his instrument readings to what these readings would be in another reference frame than his own. Thus, two observers, performing transformations, can verify that they agree on the underlying physics.

The invariance principle of relativistic physics is that in all reference frames the same physics is going on.

An example from the history of phyisics. Before 1900 it was widely known in the physics community that the Maxwell equations are not invariant under galilean transformation. That seemed to indicate that going from one velocity to another, the physics of elektromagnetism would change. Lorentz showed that there is a set of transformations under which the Maxwell equations are invariant, these transformations are known as the Lorentz transformations. Einstein concluded that the Lorentz transformations are the fundamental transformations between inertial reference frames. Thus the central principle of relativistic physics is satisfied: in all reference frames, the same physics is going on. Any hypothesis that doesn't satisfy that criterium is alien to relativistic phyisics. --Cleon Teunissen 11:33, 11 Feb 2005 (UTC)

Variance theory is the opposite of the relativistic physics

But this does not address the deeper issue. Your paradigm is a different one. Your physics paradigm is alien to general relativity. --Cleon Teunissen 22:32, 10 Feb 2005 (UTC)

(William M. Connolley 17:20, 11 Feb 2005 (UTC)) I disagree. But I think yours is...
I think the paradigm you believe in is 'variance theory'. I call it variance theory because it is the opposite of the invariance principle of relativistic phyisics. I get the impression that you believe that a coordinate transform is an act with physical consequences. In variance theory, coriolis force and centrifugal force are considered to be the result of a coordinate transform. Conversely, according to variance theory it is possible to make a force disappear with the help of a suitable coordinate transform.
Can you confirm that this is your belief system?
According to relativistic phyiscs, the same physics is going on in all references frames. Or, phrased in another way: according to relativistic physics, laws exist (and they are found by physicists) that are invariant under transformation, they are valid in all reference frames.
Do you reject the invariance principle?
Second question: is there something that would falsify your theory? What is your explanation of the behavior of gyroscopes? I insist that you show how your theory takes account of the behavior of gyroscopes. All frictionfree mounted gyroscopes on Earth will, after they have been spun up, display the sidereal rotation period of Earth, 23 hours, 56 minutes, 4 seconds. How do they obtain that information? --Cleon Teunissen 08:01, 12 Feb 2005 (UTC)

The no original research guidelines

You are coming very close to (may have exceeded) the "no original research" guidelines. Wiki is not here for your personal opinions (or mine) but to report what is out there. (William M. Connolley 17:20, 11 Feb 2005 (UTC))

That is an important guideline. Let me discuss an example where that guideline was neglected. In weather patterns the coriolis effect is causing air movement that would be absent on a non-rotating planet. In calculating weather, it must be taken into account that on Earth the manifestation of inertia is doing work.
Yet in the coriolis effect article somebody stated that 'coriolis force doesn't do work'. This opinion is novel, and it is wrong: the coriolis effect is causing air movement that would be absent on a non-rotating planet; work is being done.
I support the policy that Wiki should report what is out there, and not personal opinions.
In science, I believe that Wiki should report the best that is out there. I mean: in science Wiki should not report folklore, it should report the best of scientific knowledge. For example, I think the Wiki article on 'tidal forces' (that you have contributed to) is excellent. Many if not most books and articles get it wrong, the current wikipedia article gets it right. (Explaining that a gravity gradient alone is sufficient for a tidal effect, and subseqently explaining in what way the geometry of orbiting contributes to tidal effect.) --Cleon Teunissen 08:33, 12 Feb 2005 (UTC)

GPS incorporates the Sagnac effect for optimal accuracy

--Cleon Teunissen 21:57, 15 Feb 2005 (UTC)
The Global Positioning System is incredibly precise, its accuracy is being pushed to below the one meter range. GPS achieves its accuracy by correcting for a range of effects, among them the geometric phenomenon called Sagnac effect. A GPS around a non-rotating planet would not have to deal with a Sagnac effect.

The non-rotating reference frame is the only frame in which there is no Sagnac effect; this is one of the ways rotating reference frames can be distinguished from each other. The angular velocity of a reference frame can be measured by several methods, one of which is to measure the magnitude of the Sagnac effect in that reference frame.

The laws of physics are identical in all inertial reference frames: this does not extend to rotating reference frames. This is of course recognized in general relativity. Special relativity was developed in response to the finding that all available evidence indicates that the same physics is going on in all inertial reference frames. General relativity is called general because it provides a complete set of mathematical tools for all transformations, whereas special relativity only covers the relativity that is expressed in the Lorentz transformations. In other words: general relativity not only describes gravity, but it also enables physicists to calculate for example the relativistic coriolis effect. (And general relativity predicts that the Sagnac effect, like all other physics, will be subject to frame dragging, whenever there is frame dragging.)

Rotating reference frames are distinguishable. Therefore rotating reference frames are not equivalent for describing physics. --Cleon Teunissen 21:57, 15 Feb 2005 (UTC)


The following text is from an article by Neil Ashby. Source of the article: Reference frames and the Sagnac effect

Now consider a process in which observers in the rotating frame attempt to use Einstein synchronization (that is, the principle of the constancy of the speed of light) to establish a network of synchronized clocks.
Observers fixed on the earth, who were unaware of earth rotation, would use just use the coordinate distance for synchronizing their clock network. Observers at rest in the underlying inertial frame would say that this leads to significant path-dependent inconsistencies, which are proportional to the projected area encompassed by the path. Consider, for example, a synchronization process that follows earth’s equator in the eastwards direction.
From the underlying inertial frame, this can be regarded as the additional travel time required by light to catch up to the moving reference point. Simple-minded use of Einstein synchronization in the rotating frame uses only the coordinate distance, and thus leads to a significant error. Traversing the equator once eastward, the last clock in the synchronization path would lag the first clock by 207.4 nanoseconds. Traversing the equator once westward, the last clock in the synchronization path would lead the first clock by 207.4 nanoseconds.
In an inertial frame a portable clock can be used to disseminate time. The clock must be moved so slowly that changes in the moving clock’s rate due to time dilation, relative to a reference clock at rest on earth’s surface, are extremely small. On the other hand, observers in a rotating frame who attempt this, find that the proper time elapsed on the portable clock is affected by earth&'s rotation rate.
Path-dependent discrepancies in the rotating frame are thus inescapable whether one uses light or portable clocks to disseminate time, while synchronization in the underlying inertial frame using either process is self-consistent.
GPS can be used to compare times on two earth-fixed clocks when a single satellite is in view from both locations. This is the common-view method of comparison of Primary standards, whose locations on earth's surface are usually known very accurately in advance from ground-based surveys. Signals from a single GPS satellite in common view of receivers at the two locations provide enough information to determine the time difference between the two local clocks. The Sagnac effect is very important in making such comparisons, as it can amount to hundreds of nanoseconds, depending on the geometry. In 1984 GPS satellites 3, 4, 6, and 8 were used in simultaneous common view between three pairs of earth timing centers, to accomplish closure in performing an around-the-world Sagnac experiment. The centers were the National Bureau of Standards (NBS) in Boulder, CO, Physikalisch-Technische Bundes-anstalt (PTB) in Braunschweig, West Germany, and Tokyo Astronomical Observatory (TAO). The size of the Sagnac correction varied from 240 to 350 ns. Enough data were collected to perform 90 independent circumnavigations. The actual mean value of the residual obtained after adding the three pairs of time differences was 5 ns, which was less than 2 percent of the magnitude of the calculated total Sagnac effect.


External link: Reflections on Relativity, by Jonathan Vos Post section 2.7 The Sagnac effect.

External link: Ring interferometry experiment. University of Canterbury, New Zealand

External link to a PDF document (1,086 KB) featuring the 1984 GPS validation of the predicted Sagnac effect. IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT

External link: GPS overview According to this source, the first GPS satellites that were launched could switch to either a newtonian compliant mode, or a relativistic compliant mode. It soon became clear that the system had to comply with general relativity in order to be accurate.

The part ot the article on general relativity has been moved

I have shortened the article by moving the 'general relativity' section. The method I used is an improvisation, and probably a method that is recommended against. I have used image space for extra article length.

I have modeled this on the tidal force article, where the reader can follow a link to a larger image. The page with that image has some explanatory text.

If there are disadvantages to this method that I am unaware of please inform me. My guess is that image space is not to be used for article; I guess on that page the history won't be recorded.

I hope there is another way of achieving this. I don't think it is enough just to link to the general relativity article, for that article does not focus on discussing the similarity and difference between gravity and fictitious force.~--Cleon Teunissen 13:16, 16 Feb 2005 (UTC)

I moved it back; it was not a good idea. --Cleon Teunissen 16:51, 20 Feb 2005 (UTC)

Perp to V

(William M. Connolley 20:03, 23 Mar 2005 (UTC)) Coriolis is f K cross V. It is always perpendicular to the motion, independent of what the motion is. Indeed, since the coriolis is an instantaneous force (so to speak) it doesn't "know" if the motion is circular or not, not being able to perceive the past or the future.

The coriolis force is certainly perpendicular to the direction of motion in the case of inertial wind. When the motion is inertial, when only the coriolis effect is involved, the coriolis force is perpendicular to the direction of motion.
But when a mechanical force tends to accelerate an object in one direction, while a coriolis force tends to accelerate it in another direction, what is the formula then? What formula describes that dynamic equilibrium? That is a more complicated situation than in the case of centrifugal force.
When motion is circular the direction of acceleration is perpendicular to the direction of velocity. In other non-circular motion, the direction of accelereation is at another angle than perpendicular to the direction of velocity. I'm not sure how that affects the coriolis inertia.
We may not be using exactly the same demarcation of 'centrifugal force' and 'coriolis force' I have encountered two quite different conventions: Coriolis_effect#Defining_coriolis_force
--Cleon Teunissen | Talk 14:37, 24 Mar 2005 (UTC)
The analysis of Dragon flight of the Lorentz force example was good. I will remove the remark about not perpendicular. --Cleon Teunissen | Talk 14:43, 24 Mar 2005 (UTC)

Revert

I've long disliked CTs version of this article, as the "discussion" above makes clear. I've really never been sure that he knows what he is talking about, and following the discussion at coriolis effect and Inertial frame of reference has made me even more doubtful. CTs articles are characterised by the "image a spaceship" style of writing, which I find very unhelpful and handwavy. So... here is my preferred version. William M. Connolley 14:56:54, 2005-08-02 (UTC).

I will not contest the reversion. However, much of the ground that Cleon was trying to cover is valid. The examples of what you feel when a car accelerates are good ones, and I call for that material to be restored to this page, but in context with what is now here and in a more conpact form.
I have updated the GR-related part of this a bit. --EMS | Talk 16:23, 2 August 2005 (UTC)
OK. Thanks for taking a look. I too won't contest the re-introduction of some of CTs stuff in context and (as you say) more compact. I'm taking your Therefore gravity acts like a fictitious force, and in general relativity, it is one. on faith, since my GR doesn't go nearly that far. Is that (forgive me) a generally recognised view of gravity in GR? I suppose I mean, does anyone call it "fictitious" in papers and suchlike? William M. Connolley 17:23:16, 2005-08-02 (UTC).
Under the equivalence principle as it was originally stated, freefall is inertial motion. Therefore gravity is not a real force in general relativity. I don't know that anyone actually calls gravity "fictitious". After all, that is not going to keep you from getting killed if you jump off a cliff. However, it is a key insight of Einstein's that it is in the same "boat" as centrifugal "force", etc.
If you really don't like it, you can delete it. I won't mind that. What I do mind in GR being brought up incorrectly. --EMS | Talk 19:00, 2 August 2005 (UTC)
Sorry: I wasn't complaining. You know more about it than me: I was trying to understand it for myself. William M. Connolley 19:23:15, 2005-08-02 (UTC).
No need to apologize. I did mean to accuse you of complaining. Instead, it is a matter that I debated between removing or updating the GR part of this article. Gravity as a "pseudo-force" is relevant but it is also a subtle point (as well as being amazing). If it seems to be causing people grief, then feel free to remove it. It is nice to have, but it does not need to be here. --EMS | Talk 20:42, 2 August 2005 (UTC)
I'm happy with it in. Can you (for my own enlightenment really rather than the article) point me towards any kind of discussion of gravity-as-a-psuedo force (if at all possible, with comparisons to Coriolis) in any of the sci literature (it would even be worth renewing my university library card for...). William M. Connolley 22:22:16, 2005-08-02 (UTC).
I would advise an introductory general relativity book. See general relativity resources. --EMS | Talk 03:51, 3 August 2005 (UTC)
I sometimes get the impression that William M Connolley feels that 'coriolis force' ought to be recognized as a fundamental force in itself. William M Connolley has expressed serious doubts whether any of the current meanings of "fictitious" applies at all for 'coriolis force'.
William M Connolley doesn't commit himself, and I think he should: there are the four fundamental interactions of nature: Gravitation, Electromagnetism, w. nuclear, s. nuclear. Does William M Connolley feel that 'coriolis force' ought to be recognized as a fifth fundamental?
Of course, coriolis does not constitute a fifth fundamental, looking at coriolis is looking at the role that inertia plays in motion, which of course is a very important role. --Cleon Teunissen | Talk 08:16, 3 August 2005 (UTC)

EMS - thanks. CT: you're talking nonsense. William M. Connolley 17:19:33, 2005-08-03 (UTC).