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Length contraction depends on the distance of the object?

  1. Oct 3, 2008 #1
    [​IMG]

    Not exactly homework, but a problem I found in my lecture notes. The train is moving at a constant speed 0.5c. Question b asks what the length of the train will be then at t = -1. From what I understand, this suggests that length contraction depends on the distance the object is away from an observer? So at t = -5 the length contraction would be different?
     
  2. jcsd
  3. Oct 3, 2008 #2

    Doc Al

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    Staff: Mentor

    It seems that this problem is asking about the visual appearance of length contraction as seen by a particular observer, not the actual measured length contraction--which is obtained after accounting for light travel time and is the same for all observers within a frame. The actual measured--not just "seen"--length contraction does not depend on distance from any particular observer, since it's not a simple visual effect.
     
  4. Oct 3, 2008 #3
    Thanks for your answer. I'm just trying to visualize what is going on and so I made a drawing. Can you tell me if this is in any way resembles what is actually going on?

    [​IMG]

    The green line would be the length Bob observes, while the black thingy denotes the actual length of the train.
     
  5. Oct 4, 2008 #4

    Doc Al

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    Redraw your diagram to show the worldlines of the front and rear of the train. They should be parallel, but not overlapping.
     
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