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Reaction time for a long bar

  1. Sep 21, 2013 #1
    Hello guys,

    The title might be slightly misleading, it's not related to general physics. It's a hypothetical question that's far from being realistic of practical;
    Suppose you have a very very long bar, and suppose it's layed on a type of material with no friction, a person stands at the 1st extremity A of the bar and pushes it, how will the other extremity B react?
    Please note that the lenght here is theoretical (consider it like 1 AU and the bar is layed on some gigatic planet or whatever), if the action happened at A at t0, how long does it take to reach B?
    Does the force that pushed the bar at A have a propagation time through the bar? Or does it happen instantly? And if not, what are the parameters that determines this reaction time? (density of the bar, etc..)
    If this question have been answered somewhere else, please put a link so I can follow it's details.

  2. jcsd
  3. Sep 21, 2013 #2
    See https://www.physicsforums.com/showthread.php?t=536289 [Broken]
    Last edited by a moderator: May 6, 2017
  4. Sep 21, 2013 #3
    Thanks for the post.
    I suspected it would have to do with the bosons (in this case photon) that travels at c:
    " all materials, even unobtainium, are held together by electromagnetic forces at the molecular level. When one molecule moves then the change in its electromagnetic field propagates to its neighboring molecule at the speed of light."
  5. Sep 21, 2013 #4

    Vanadium 50

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    Nor is it related to quantum physics. Moved.
  6. Sep 21, 2013 #5


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    See also https://www.physicsforums.com/showthread.php?t=558506. The motion of a rigid body is limited by the compression wave velocity - or speed of sound in that particular media. Needless to say, there is no known media where the speed of sound is even close to the speed of light.
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