Timeline for Where does length contraction occur towards?
Current License: CC BY-SA 4.0
13 events
| when toggle format | what | by | license | comment | |
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| Jun 1 at 15:47 | comment | added | WillO | @fishinear : Clearly we agree on the physics, but I do not see the OP asking the very specific question that you are seeing. | |
| Jun 1 at 14:31 | comment | added | fishinear | @WillO I can agree on that. But it does not invalidate my original comment. You state in the answer that you can accelerate the rod in any way you want. But the OP asks about the very specific way that is needed to keep the proper length of the rod the same. Your answer is not incorrect, I just thought it could be improved by explicitly addressing that way. | |
| Jun 1 at 14:19 | comment | added | WillO | @fishinear : We might be using the phrase "physical stress" slightly differently. My point (and I think you agree) is that in any frame where the rod changes length, it must change length because forces were applied to it, and the details of how it changes length must depend on the details of how those forces were applied. | |
| Jun 1 at 14:12 | comment | added | fishinear | @WillO By applying forces to it, yes, but no physical stress. That is, no (extra) internal forces inside the material. When accelerating each point of the rod differently, when done correctly that does not lead to physical stress in the rod, that is, no change in proper length of the rod. | |
| Jun 1 at 13:34 | comment | added | WillO | @fishinear: But your acceleration protocol causes the rod to shrink in the "stationary" frame, by applying physical stresses to it in that frame. If you accelerate a rod, then its length has to change in some frame (that frame depends of course on how you accelerate it). And that change in length is caused by physical stress in that frame. What else could cause it? (Of course if the rod has never accelerates, then it has different lengths in different frames and no physical stress is involved --- but that's not what the OP is asking about.) | |
| Jun 1 at 10:30 | comment | added | fishinear | @WillO That is, you apply the exact acceleration required on each point of the rod, such that its proper length stays the same. That way, there is no physical stress induced on the rod. That requires the back side to be accelerated more than the front side, of course. | |
| Jun 1 at 10:12 | comment | added | fishinear | @WillO Apparent length contraction of a moving object in Special Relativity does not induce and is not due to physics stress in the object. That is an example of changing length without physical stress, which is what the OP was asking about. | |
| May 31 at 2:47 | comment | added | WillO | @fishinear: Nothing changes length for any reason other than physical stresses. Of course those stresses (and the resulting length change) are frame dependent and relativity tells you how to compare them across frames. But the analysis in a single frame (as the OP is asking for) is strictly about the effects of pushing and pulling. | |
| May 5 at 16:12 | comment | added | fishinear | Good answer, but I think it is clear from the OP's question that he means a type of acceleration that does not induce physical stresses in the rod. That is, the resulting length contraction is purely due to relativistic effects, and not due to physical stresses. | |
| May 3 at 13:31 | comment | added | Arthur | Right, I was thinking about the (non-inertial) reference frame of the rod itself. In the inertial frame that the rod eventually catches up to, you are right, of course, the front started accelerating first. | |
| May 3 at 13:15 | comment | added | WillO | @Arthur: "the frame of the now-accelerated rod" means the inertial frame of the rod after the rod has accelerated. In thag frame, the front accelerated first.9 | |
| May 3 at 10:31 | comment | added | Arthur | "But in the frame of the now-accelerated rod, the acceleration at the front started before the acceleration at the back" This is not true. At the time when the acceleration starts, there is no velocity difference between the frames of reference, so the stationary inertial observer and the rod will agree that the entire rod starts accelerating simultaneously. On the other hand, the front end will accelerate faster than the back end, according to the rod itself. | |
| May 3 at 1:21 | history | answered | WillO | CC BY-SA 4.0 |