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A taut rope pulled - delay on the other end?

  1. Aug 10, 2011 #1
    My father and I were just having a conversation. The scenario he presented to me was this;

    There are 2 ropes fixed on 3 points, like so:


    The distance of AB is approximately 10 meters, while BC is approximately 100 meters long. Given that both ropes are being pulled with the same amount of force and already taut, how would point B react if both A and C increased force at the same time in the same increment? More specifically, would point B feel the pull of both A and C at the same time, or would there be a slight delay? Would either pull take time to be recognized, or would it be immediate?

    The next question is, if the pull from both A and C is felt by B at the same time, would this property apply along an infinitely longer length? For example, a light year.
    If not, is there an equation (perfect world, of course) that would explain any delay between the pull of A and/or C and the reaction of B, in relation to the length of both ropes?
  2. jcsd
  3. Aug 10, 2011 #2


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    Tension in the rope would propagate at about the speed of sound in the rope.
  4. Aug 10, 2011 #3
    To add to what rcgldr said (which is correct), that speed of sound is determined by the electromagnetic forces holding the atoms together, so the speed of light is a theoretical upper-limit on the speed of sound.

    The tensions felt at point B would simply be felt at different times. You can calculate the times based on the lengths of the rope segments and the speed of sound in the rope.
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