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Natural Science Forum / Physics / Relativity / February 2007Magnetism and SR - how is this explained
I'm posting this problem in simpler form. I haven't found how observers in a moving frame explain what occurs using Einstein's notions of space and time. There is a circular disk rotating in the X-Y plane of the rest frame. The disk is centered at x=0, y=0. As measured in the rest frame there is an iron rod positioned along a diameter of the disk. There is a moving frame with velocity V moving along the x-axis relative to the rest frame. For observers in this frame, according to Einstein, when one end of the iron rod is at x=R, where R is the radius of the disk, the coordinate of the other end is not on the x-axis (These events are not simultaneous events in the moving frame since they are separated by 2R and are simultaneous events in the rest frame). The moving frame observers do not measure this iron rod to be a straight line. Let this iron rod be weakly glued to the disk. And let there be two weak magnets in the rest frame. These magnets cannot pick up the iron rod from the rotating disk unless all segments of the magnet are aligned with the iron rod. One magnet is a straight line the length of the diameter of the disk. The other magnet is shaped to be identical to what the moving observer measures the shape of the iron rod to be when one end of the rod is at x=R. If the moving observer is instructed to use one of these rest magnets to remove the iron rod from the rotating disk, and at least one end of the magnet must be on the x-axis at x=R (as measured in the rest frame), and the the magnet must have zero velocity relative to the rest frame, should the moving frame observer choose the magnet shape where all segments of the magnet are simultaneously aligned with the iron rod as he has measured it in the moving frame, or should he choose the straight magnet which he measures to be only partially aligned to the iron rod? Since the only magnet that works per the given information in the problem is the straight magnet, how does the moving observer explain the fact that if less points of the magnet are aligned with the rotating iron rod, the iron rod can be removed from the disk? And also if all points of the magnet (as per the shape of the other magnet) are simultaneously aligned with the iron rod, the magnet is not strong enough to remove the iron rod from the disk? Dave Seppala > I'm posting this problem in simpler form. I haven't found how > observers in a moving frame explain what occurs using Einstein's [quoted text clipped - 40 lines] > > Dave Seppala Einstein's notions were the same as Maxwell's. Time-independent Maxwell equations Time-dependent Maxwell's equations Relativity and electromagnetism http://farside.ph.utexas.edu/teaching/em/lectures/lectures.html Maxwell's equations in classic electrodynamics (classic field theory)_ a) Maxwell equations (no movement), b) Maxwell equations (with moved bodies) http://www.wolfram-stanek.de/maxwell_equations.htm#maxwell_classic_extended http://web.mit.edu/8.02t/www/802TEAL3D/visualizations/light/index.htm http://www.ee.surrey.ac.uk/Personal/D.Jefferies/antennas.html Sue... > I'm posting this problem in simpler form. I haven't found how > observers in a moving frame explain what occurs using Einstein's [quoted text clipped - 40 lines] > > Dave Seppala Simple. Just use the Lorentz transformations for EM fields. >> I'm posting this problem in simpler form. I haven't found how >> observers in a moving frame explain what occurs using Einstein's [quoted text clipped - 42 lines] > > Simple. Just use the Lorentz transformations for EM fields. Simple-minded moron, you cannot derive the cuckoo malformations, fuckhead. > I'm posting this problem in simpler form. :) I haven't found how > observers in a moving frame explain what occurs using Einstein's > notions of space and time. They "explain" what occurs in the same way that observers in non-moving frames do, since all observe the *same occurences*, albeit from different perspectives. How do the American football spectators whose seats are in-line with the goal posts, explain field goals? > There is a circular disk rotating in the X-Y plane of the rest frame. > The disk is centered at x=0, y=0. As measured in the rest frame [quoted text clipped - 36 lines] > > Dave Seppala >> I'm posting this problem in simpler form. > [quoted text clipped - 10 lines] > How do the American football spectators whose seats are in-line with the > goal posts, explain field goals? Brilliant :-) Dirk Vdm > > I'm posting this problem in simpler form. > [quoted text clipped - 9 lines] > How do the American football spectators whose seats are in-line with the > goal posts, explain field goals? Would a football travelling at the speed of light through the goal posts see that I have two eyes? >> I'm posting this problem in simpler form. > [quoted text clipped - 10 lines] >How do the American football spectators whose seats are in-line with the >goal posts, explain field goals? The spectators can take in all the information. They actually have a three dimensional view of the field, albeit in your analogy they cannot determine by one point in space whether or not there was a field goal. But if they are aligned with the goal posts, they can view the football's trajectory, the three dimensions of the field, etc, the location of the players and officials, their reaction and the crowd's reaction and come to a valid conclusion based on all aspects of the problem. But why do the moving frame observers think that a magnet that is simultaneously aligned with all points of an iron rod exerts less force on the rod than a magnet that is not-simultaneously aligned with all points of the iron rod? David >> There is a circular disk rotating in the X-Y plane of the rest frame. >> The disk is centered at x=0, y=0. As measured in the rest frame [quoted text clipped - 36 lines] >> >> Dave Seppala >>>I'm posting this problem in simpler form. >> [quoted text clipped - 20 lines] > crowd's reaction and come to a valid conclusion based on all aspects > of the problem. Which is the point. The spectators don't "explain" the occurence of a field goal any differently than the referees do (i.e. the ball travels between a pair of goal posts), despite the fact that they describe the occurence differently. > But why do the moving frame observers think that a magnet that is > simultaneously aligned with all points of an iron rod exerts less > force on the rod than a magnet that is not-simultaneously aligned with > all points of the iron rod? Here's a simpler problem. Assume there's a theory T which indicates that if tall observers measure a particular collection of events E as m, then short observers will measure E as m+4. Now suppose a tall observer O happens to measure that particular collection of events E as 7. Then, according to theory T, a short observer O' will measure E as 11. How does O' /explain/ that the measurement is 11? Got an answer for that? Then here's a generalized version of your problem. Suppose a non-moving observer O views a series of events E and makes a collection of measurements M based on E. Then, according to the theory of Relativity, an observer O', who's moving relative to O, will make a corresponding set of measurements M' upon viewing E. How does O' /explain/ M'? Did you notice that the two problems are essentially the same? And the "explanation", in each case, is that the measurement(s) logically follow(s) from the given information using the applicable theory, which is the only sort of explanation that's possible in Physics. Now perhaps you think that there may be some current theory other than Relativity that could indicate the measurement(s) of O' will be different than M'. However, that simply can't be the case as long as the /given/ measurements of O (i.e. M) are consistent with current theory, since Relativity is the *only* current theory that relates the measurements of relatively moving observers. > David > [quoted text clipped - 38 lines] >>> >>>Dave Seppala >>>>I'm posting this problem in simpler form. >>> [quoted text clipped - 43 lines] > >Got an answer for that? Jem, I am not asking how does someone in one frame explain the measurement in another frame. I am asking how does someone in an inertial frame measure that when all points of a magnet simutlaneously align with all points of an iron rod as measured in his own frame that magnet exerts less force on the iron rod then when all points of the magnet are not simultaneously aligned with the iron rod as measured in the same frame. In your responses, you keep asking how does one frame explain the measurements of another's frame - that is not what I am asking. David >Then here's a generalized version of your problem. > [quoted text clipped - 59 lines] >>>> >>>>Dave Seppala [..] Why do you never actually try to solve your own problems, David? >>>>>I'm posting this problem in simpler form. >>>> [quoted text clipped - 53 lines] > In your responses, you keep asking how does one frame explain the > measurements of another's frame - that is not what I am asking. If that weren't what you were asking then your question couldn't be answered by SR, because the only thing SR can tell you is how the measurements of one observer relate to the measurements of another observer. In particular, other than such measurement /relationships/, SR says nothing about the effects of electromagnetism (except for perhaps a specification of the speed of light in vacuum). At any rate, it /is/ what you're asking. The implication of your question (and of all your Rube Goldberg inspired questions) is that you can understand the effects as seen from the standpoint of a stationary observer, but you can't understand them from the standpoint of a moving observer. And that's the issue my previous posts in this thread have addressed. > David > [quoted text clipped - 61 lines] >>>>> >>>>>Dave Seppala >>>>>>I'm posting this problem in simpler form. >>>>> [quoted text clipped - 60 lines] >SR says nothing about the effects of electromagnetism (except for >perhaps a specification of the speed of light in vacuum). If the moving observer cuts a straight line segment out of the disk along the x-axis by cutting all points simultaneously, and he also stops the rotation of this line segment by stopping all points simultaneously, he finds that he does not end up with a straight line segment. If there are just two points rotating around a circle in a rest frame, and they happen to both cross the x-axis simultaneously as viewed by a frame moving with V along the x-axis, and there is a rod in the rest frame that spans those two points, that length of that rod is longer than the span of those two points - if the masses of rotating objects are large, the rod will be compressed if it is attached to the rotating masses, and it will no longer be straight. You say that makes perfect sense to the moving observer because its a consequence of Einstein's equations. He can cut and stop all points on a straight line segment, and that segment will not be a straight line. That consequence of Einstein's theory simply doesn't make sense to me. So you must have a consequence or series of consequences from special relativity which are so logically powerful that they permit you to accept consequences like the above. What are those experiments that let you override these consequences? David >At any rate, it /is/ what you're asking. The implication of your >question (and of all your Rube Goldberg inspired questions) is that you [quoted text clipped - 68 lines] >>>>>> >>>>>>Dave Seppala > >>>>>>I'm posting this problem in simpler form. > [quoted text clipped - 83 lines] > that let you override these consequences? > David Oh gee David, I don't know. Why don't you actually do some research? Perhaps go to a library? Maybe then you will understand why relativity is accepted. http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html While your there, why not pick up a book on relativity so you can stop pestering this newsgroup with your unimaginative problems. Every few weeks, its the same thing. A rotating cylinder, a rotating disk - no change, no imagination, and you show no sign of having learned from the last ten thousand rotating <whatever> problems you asked. [snip] >>>>>>>I'm posting this problem in simpler form. >>>>>> [quoted text clipped - 81 lines] > special relativity which are so logically powerful that they permit > you to accept consequences like the above. The "powerful logic" is that onlookers don't affect events. All SR does is relate the measurements of observers with different perspectives. IOW, you have to /specify/ what somebody measures in order to get the theory to tell you what anybody measures, and whether the results the theory tells you are feasible depends solely on whether the measurements that you specified are feasible*. * as was explained in more detail earlier in this thread, there simply is no other basis for determining the feasibility. What are those experiments > that let you override these consequences? > David [quoted text clipped - 71 lines] >>>>>>> >>>>>>>Dave Seppala > I'm posting this problem in simpler form. I haven't found how > observers in a moving frame explain what occurs using Einstein's [quoted text clipped - 17 lines] > rod from the rotating disk unless all segments of the magnet are > aligned with the iron rod. Do you mean all segments of the magnet are aligned with the iron rod *at the same time*, or do you mean that one small segment of the magnet can pick up one small segment of the rod if the small segments are aligned? You see, the first constraint on the magnet (that the global shape of the magnet and rod must be the same) is impossible, given Maxwell's equations. Each part of the magnet and rod must act locally, without influences faster than the speed of light. What will happen is that, in the rest frame, an observer will see the magnet pick up the entire rod at the same time, but will note that due to speed of light constraints each part of the rod must have been picked up by a local interaction. In the other frame, the observers will see each small segment of the rod get attracted to each small segment of the magnet, as the rod rotates under the magnet. They will stick when they get aligned, non- simultaneously. The details of the magnetic field really have no relevance beyond a discussion of the details of which field actually causes the attraction. Relativity of simultaneity saves the day again! (As well as rejecting the notion of absolutely rigid bodies.) > One magnet is a straight line the length > of the diameter of the disk. The other magnet is shaped to be [quoted text clipped - 20 lines] > > Dave Seppala >> I'm posting this problem in simpler form. I haven't found how >> observers in a moving frame explain what occurs using Einstein's [quoted text clipped - 37 lines] >rotates under the magnet. They will stick when they get aligned, non- >simultaneously. Why doesn't this moving frame think the magnet (of the rest frame) that is identical to the shape of the iron rod in which all points of the magnet are simultaneously aligned (in the moving frame) with all points of the iron rod on the rotating disk exerts a greater force on the iron rod than a magnet that is non-simultaneously aligned to the iron rod. That's what I don't see. David >The details of the magnetic field really have no relevance beyond a >discussion of the details of which field actually causes the [quoted text clipped - 27 lines] >> >> Dave Seppala > I'm posting this problem in simpler form. I haven't found how > observers in a moving frame explain what occurs using Einstein's > notions of space and time. > > There is a circular disk rotating [...] Gee, another rotating disk problem from David Seppala. |
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