Talk:Fictitious force/Archive 2

message: :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:<BR>
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.<BR>
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)
thread_title:  When is a force doing work? 

message: What a legacy Einstein left us!<BR>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.<BR> 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)
thread_title:  the Feb 2 version of the article. 

message: Cleon Teunissen 16:02, 9 Feb 2005 (UTC)
thread_title:  The importance of inertia 

message: Cleon Teunissen 11:33, 11 Feb 2005 (UTC)
thread_title:  The invariance principle of relativistic physics 

message: 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)
replies: text: I moved it back; it was not a good idea. --Cleon Teunissen 16:51, 20 Feb 2005 (UTC)
thread_title:  The part ot the article on general relativity has been moved 

message: William M. Connolley, your first edit to this article included the statement "Simply characterising a force as fictitious because it arises from a change of reference is not reasonable."  What is your basis for this claim?  ‣ᓛᖁ[ ᑐ] 06:10, 21 September 2005 (UTC)
replies: text: Because that is an entirely arbitrary choice of definition. William M. Connolley 08:17, 21 September 2005 (UTC)
replies: text:  Do you have a source that supports this?  ‣ᓛᖁ[ ᑐ] 08:20, 21 September 2005 (UTC)
replies: text: I disagree with the idea that it is arbitrary; a real force in classical mechanics requires an interaction.  On the other hand since not everyone likes using the idea of a fictitious force, do you have any source that claims it is not reasonable? Salsb 11:47, 21 September 2005 (UTC)
thread_title:  Validity 

message: William has raised one very good point.  This article is poorly-written, and it may be confusing to people who don't know already what it's talking about.  I've worked on the intro, but that's it so far.  I'll do more, but hopefully I can get some help.  -- SCZenz 01:54, 22 September 2005 (UTC)
replies: text: Yes. The article is very poorly written. Why was why reverting to this version was a very bad idea. William M. Connolley 08:40, 22 September 2005 (UTC)

text: I agree. I think the examples should probably just be blanked and started over again. Salsb 12:33, 22 September 2005 (UTC)
replies: text:  The examples are valuable; they do make the concept easier to understand, even if they could be better.  If one could be cleaned up and made concise (preferably regarding centrifugal force, as that seems most obviously fictitious), and placed before the formulas begin, it would be very helpful to laypeople.  ‣ᓛᖁ[ ᑐ] 12:51, 22 September 2005 (UTC)

text:  I disagree with blanking them.  I think they can be fixed, but seriously rewritten of course.  -- SCZenz 13:15, 22 September 2005 (UTC)

text: I also just added a section on fictitious forces as they arise from rotating references frames. I followed Kleppner, since the section above did, but the derivation is essentially identical in Fetter and Landau, along with the admonishments, about the forces not being real, and presumeably in any other mechanics text, although I only cited the ones I have on had to consult. I had to hurry at the end, since I'm supposed to be in a meeting one minute ago, but if someone could make the equations look nicer, I would apprecitate it. Salsb 12:33, 22 September 2005 (UTC)
replies: text:  I think we should be careful about making this article too much more technical than it now is.  We need to have examples of applications and real-world effects, and move them to the top. -- SCZenz 13:15, 22 September 2005 (UTC)
replies: text: I agree, I think its pretty much at the limits of technicality. I put it in mostly to make it obvious -- to the mathematically able -- where the fictitious forces arise, and since there was a request for more citations, as this is a concept found in essentially every intro mechanics book. It might be fruitful to move the technical parts to the end, so readers get the examples then the math. Salsb 13:58, 22 September 2005 (UTC)
replies: text: I went ahead and reorganized the sections. It still needs ample work, but thats all I can do for now Salsb 14:18, 22 September 2005 (UTC)

text: I have rewritten "acceleration in a straight line" to be a useful general illustration of the concept.  Does it serve this purpose?  Are there other comments? -- SCZenz 18:05, 22 September 2005 (UTC)
thread_title:  Cleanup 

message: OK, you're right there - I read through too quickly. I agree: within newtonian mechanics this provides a consistent definition. I maintain my other objections. William M. Connolley 18:34, 22 September 2005 (UTC)
replies: text: Ok, I claim there is also a consistent definition in generally relativity, that is also mathematical.  Unfortunately, writing it down would be too complex, especially since forces and reference frames are handled differently in GR.  (Plus it would take me many hours of reading to understand it, I suspect.)  I can certainly find a book that goes over this, and cite it, however. -- SCZenz 19:00, 22 September 2005 (UTC)

text: I'd like to note, though, that there is not consistent mathematical definition between newtonian mechanics and GR, again because reference frames, forces, and equations of motion are handled differently in the two theories.  The definitions would be conceptually equivalent, however.  The question of whether gravity is a fictitious force in GR arises from the fact that gravity is not a true force in GR.  (iIn non-inertial reference frames, there is no force of gravity, although obviously objects still fall into each other.)  -- SCZenz 19:00, 22 September 2005 (UTC)
thread_title:  No problem within Newtonian mechanics 

message: Does it at all? Or are you refering to frame-dragging here, or is there some other case? GangofOne 00:34, 23 September 2005 (UTC)
thread_title: "It is extremely rare for space-time geometry to rotate significantly with respect to the universe as a whole,"

message: Even though I would like a mention of relativity to be in here, I approve of the deletion of the section on it.  I had not had much time to look it over, but once I did, I realized the SCZenz was right to want it out.  All that is needed here is a short blurb on gravity being "fictitious" under the equivalence principle of general relativity.  A few extra sentences to somewhat explain that is advisable, but discussion of the technical details of GR (such as the description of geodesics) does not belong here.
For now, my feeling is that it is best left out until this article has had a chance to stabilize and mature some more.  Then it can be brought in as an aside.  However, the editors of this page can and should be willing to veto any such addition (even if it is mine) if in their opinion it does not "fit". --EMS | Talk 22:39, 27 September 2005 (UTC)
replies: text: Heh.  I'm glad you like it.  You can quibble about the perentheticla remark, but it's important for clairty to people who don't know a lot of physics.  Also I think your quibbling would be wrong. ;)  But if you want to argue it, let's take it to user_talk pages, rather than risk fanning any more debate on this article. -- SCZenz 04:14, 28 September 2005 (UTC)
replies: text:  I am going to edit that stuff at some point, to tighten it up and make it technically correct (or at least more correct).  A major issue is how to do this in a way that enhances your excellent work instead of muddying it up again.  The existing text communicates well without being buzzwordy, and this is essential to the success of this article.  So you have left me with a interesting puzzle to work through. --EMS | Talk 16:16, 28 September 2005 (UTC)

text: My only concern now is that we have two sets of footnotes (yours, and the references), with identical labelling. ;)   Not sure what to do with that. -- SCZenz 23:05, 29 September 2005 (UTC)
replies: text:  The comments can be combined with the paper/book reference in the references. That's not my style, but sometimes you see this in scientific articles.Count Iblis 00:20, 30 September 2005 (UTC)
replies: text:  Hmm... Not my style either. And, generally, not Wikipedia's.  Let's think about it, or failing that leave it and hope nobody notices.. ;) -- SCZenz 00:25, 30 September 2005 (UTC)

text:  I did notice and correct that.  I am not sure that I like the corrections, as that is not my style either.  (I would like the letters to be in square brackets.)  However, this at least this resolves the conflict.  Unfortunately, footnoting is not robustly supported in Wikipedia at this time.  I will keep an eye out for a better way to do this, but for now I think that this the best I can do.  --EMS | Talk 03:42, 30 September 2005 (UTC)
thread_title:  Good move (removing relativity stuff) 

message: Now that I have looked at that, all that is needed is already in this article.  Indeed, this is a very well-written paragraph on it.  I can quibble with the parenthetical remark at the end noting the gravity is "real" in Newtonian physics, but I will edit that when I can.  As I see it, the use of the "force" of gravity is required in Newtonian physics, independent of whether that force is fictitious or not. --EMS | Talk 22:46, 27 September 2005 (UTC)
replies: text: Heh.  I'm glad you like it.  You can quibble about the perentheticla remark, but it's important for clairty to people who don't know a lot of physics.  Also I think your quibbling would be wrong. ;)  But if you want to argue it, let's take it to user_talk pages, rather than risk fanning any more debate on this article. -- SCZenz 04:14, 28 September 2005 (UTC)
replies: text:  I am going to edit that stuff at some point, to tighten it up and make it technically correct (or at least more correct).  A major issue is how to do this in a way that enhances your excellent work instead of muddying it up again.  The existing text communicates well without being buzzwordy, and this is essential to the success of this article.  So you have left me with a interesting puzzle to work through. --EMS | Talk 16:16, 28 September 2005 (UTC)
thread_title:  Just saw the current introduction 

message: I have put my changes in.  I think that I have succeeded in explaining how GR turns gravity into a fictitious force in the main narrative, while having put some needed elaboration into the footnotes.  So hopefully readers will be able to get the gist of what is going on in the view of general relativity.  --EMS | Talk 23:01, 29 September 2005 (UTC)
replies: text: My only concern now is that we have two sets of footnotes (yours, and the references), with identical labelling. ;)   Not sure what to do with that. -- SCZenz 23:05, 29 September 2005 (UTC)
replies: text:  The comments can be combined with the paper/book reference in the references. That's not my style, but sometimes you see this in scientific articles.Count Iblis 00:20, 30 September 2005 (UTC)
replies: text:  Hmm... Not my style either. And, generally, not Wikipedia's.  Let's think about it, or failing that leave it and hope nobody notices.. ;) -- SCZenz 00:25, 30 September 2005 (UTC)

text:  I did notice and correct that.  I am not sure that I like the corrections, as that is not my style either.  (I would like the letters to be in square brackets.)  However, this at least this resolves the conflict.  Unfortunately, footnoting is not robustly supported in Wikipedia at this time.  I will keep an eye out for a better way to do this, but for now I think that this the best I can do.  --EMS | Talk 03:42, 30 September 2005 (UTC)
thread_title:  Modifications done 

message: In the section examples of fictitious forces, this figure is included.
:
Animation: driving from block to block
In this illustration the car accelerates after a stop sign until midway up the block, at which point the driver is immediately off the accelerator and onto the brake so as to make the next stop.
For the accelerated frame this shows both the real and fictitious force. Which is incorrect in this case.
In the section gravity as a fictitious force, this is included.
:
Animation: ball that rolls off a cliff
Note: The rain frame perspective here, rather than being that of a raindrop, is more like that of a trampoline jumper whose trajectory tops out just as the ball reaches the edge of the cliff.  The shell frame perspectiveEdwin F. Taylor and John Archibald Wheeler (2000) Exploring black holes (Addison Wesley Longman, NY)  may be familiar to planet dwellers who rely minute by minute on upward physical forces from their environment, to protect them from the geometric acceleration due to curved spacetime.
For the rain frame it shows the ball going down as the rain drop falls, whereas it should be coming up because of the fictitious force in the rain frame. Including these figures, although were well intentioned, ends up misguiding the reader. These need to be revised by the uploader. --Fatka (talk) 23:20, 4 November 2008 (UTC)
thread_title:  Possible errors 

message: I have not looked at this article for ages, but I am very impressed with the way it has turned out.  My compliments to the authors. -- ALoan (Talk) 13:58, 28 November 2005 (UTC)
thread_title: Well done

message: In the introduction, it is said that the surface of the Earth is a rotating frame of reference. and at the end, that an observer on the surface of a planet (thus in general, which means the Earth too, and include the rotating as well than the non rotating planets) is in a accelerate frame.
What I understand from that, is that the rotating frame of the Earth is the accelerate frame of 'a planet'. If it is so, we are talking here of a rotating planet, not a planet having no rotation at all.
Is everybody here understand the same thing or understand it in another way? --24.202.163.194 15:33, 3 January 2006 (UTC)
thread_title:  Earth, planet and accelerated frame