How long would it take? (Physics question, sort of. Maybe)

by AlmostAtheist 39 Replies latest jw friends

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  AlmostAtheist

  Let's say I've got a length of solid material that is one light year long. It's just hanging there in space, between galaxies, not affected by gravity enough at any point along its length to be twisted, bent, whatever. Let's also say that it is resistent to flexing.

  I'm at one end of this impossibly-existing rod, and you are at the other. If I push my end toward you by an inch, how long would it take for your end to move an inch toward you? (Let's say there's a rocket engine on my end that does the pushing)

  (If this is an impossible question to answer since the set up for it is impossible, just say so. But please note what about it is impossible.)

  Dave
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  candidlynuts

  put down the bong man! lol
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  AlmostAtheist

  "Dude, this rod.. is like... HUGE...."
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  Darth Yhwh

  It would take the same amount or volume of time but because your "material" is a light year long the time between the recorded movements of both ends would be exactly a light year.
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  Darth Yhwh

  That is assuming that the coefficient of expansion and contraction across the entire length of your "material" is constant.
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  Elsewhere

  It would come down to a science called "shock wave propagation".

  What would happen is you will have a very very long compression wave propagate through the length of the object at a certain velocity..

  You also have to remember that the individual atoms in this substance will start out with a certain distance between them and then compress closer to each other which is what will propagate the wave.

  The problem you are having is that you are viewing this object as a single solid object, which is not accurate. You have to think about this object as being composed of a bunch of little atoms near each other, but not actually "touching" each other.
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  Cygnus

  It would take .0000000000001 seconds. The same amount of time it takes me consider going back to the JWs.
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  Darth Yhwh

  Elsewhere, how does shock wave propagation affect the time it takes for the material to move an inch though. Granted the shock wave propagation will increase as the length of your material increases but how much and can it be measured?
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  stevenyc

  (Takes a hit on the bong)

  Oooo.Kay!

  If the speed of light in a vacuum is a given constant, and is the fastest 'speed' any information can travel, (exhales slowly a big puff), then the other end of the rod would move no sooner than in the time it takes light to travel that distance, 1 year.

  Also, if you and the other person pushes the rod an inch at the same time, both ends would move an inch, and it would take at least 1 year before both end were back to their original position.

  steve.

  (passes the bong)
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  AlmostAtheist

  So the material would "bunch up" at the point where the thrust began, and it would spread out along the length?

  I think the same question would still be there, how long would it take to travel the length? Does such a wave travel at light speed?

  Thanks for the responses so far!

  Dave