# Transmission of energy

If you have a stick and push it from one end, the whole stick moves instantly. You have given the other end of the stick kinetic energy. So doesn't this mean that you have transmitted energy at an infinite rate, rather than at or below the speed of light?

Doc Al
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If you have a stick and push it from one end, the whole stick moves instantly.
No it doesn't. The impulse moves through the stick at about the speed of sound. So nothing is being transmitted anywhere near the speed of light, much less infinitely fast.

Doc Al:
What if you push it with a speed that's twice the speed of sound- wouldn't that mean that you could see a noticeable difference in the length of the stick, as the atoms were compressed together, if you filmed it?

Doc Al
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Doc Al:
What if you push it with a speed that's twice the speed of sound- wouldn't that mean that you could see a noticeable difference in the length of the stick, as the atoms were compressed together, if you filmed it?
I'm talking about how long it takes for a smack given to one end of a stick to travel to the other end. If you push one end of the stick, it takes time for all parts of the stick to get moving. It's not instantaneous. So, yes, the stick will be compressed a bit when you push on one end. (Push too hard and you'll just break it, though. )

What if it's in space and there's no friction- would it be transmitted faster?

Doc Al
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What if it's in space and there's no friction- would it be transmitted faster?
Not sure I understand what you're getting at with this question. I see no reason why being in space would have anything to do with it.

Ok, how about if I put it like this:
There is a long tube full of marbles which are all touching each other. I put another marble in at one end and another comes out of the other end. I have transferred kinetic energy through the marbles. How quickly was it transferred, or how long did it take between the original marble at the entry end starting to move, and the exiting marble starting to move.

Actually, forget it- I've realised my error.

russ_watters
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