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A pole one light year long .

  1. Feb 13, 2007 #1
    A pole one light year long.....

    laying in bed last night I had this question pop in to my pointy little head.

    If I had a pole one light year long sitting between points A and B and I pushed it forward one foot from point A toward point B how long would it take to move at point B?


    I've got an answer, but I'll wait to see what the people smarter than me have to say.
     
  2. jcsd
  3. Feb 13, 2007 #2

    russ_watters

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    That's a meaningless answer, funker, since no such thing exists.

    Bender, it the impulse would travel at the speed of sound in that material. For example, if the pole were steel, with a speed of sound of 4500m/s, it would take 6700 years for the impulse to reach the other end of the pole.
     
  4. Feb 13, 2007 #3

    ranger

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    Err, please dont answer like that. You are proposing faster than light communication here. If it were instantaneous, then we could send morse (poking) instantaneously, whereas light would take one year. If you hit one end of stick with a hammer, would the other end hear it instantaneously? No. You must think of the interaction at a molecular level.

    EDIT: Russ beat me to it.
     
  5. Feb 13, 2007 #4

    russ_watters

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    Huh? No, minijumbuk. You are simply wrong. Force has to be transmitted via molecular interactions. If forces propagated instantaneously, there'd be no sound because objects wouldn't oscillate. Striking a large bell with a hammer would just make it swing back and forth.

    Gravity is different, but it still propagates at the speed of light.
     
  6. Feb 13, 2007 #5

    Integral

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    I have deleted some blatentely incorrect posts.

    Locking since the question has been answered and there is no point in further discussion.
     
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