# The Effects of Moving Matter Across Light-Year distances

If I were to stand at one end of a light-year long metal pole, and another person were to stand one light-year away at the other end, and then I were to push on my end of the pole. How long would it take for their side of the pole to move? I've been told that the matter in the pole would only move at the speed of sound. So it would take however long a sound-wave takes to travel a light-year for the other person to see the pole move. But if this is true, does that mean that if you were to take any still object, and hit it with another object moving at the speed of sound, the still object would compress into itself before expanding back out again?

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I would assume the answer to your second question will depend on the compressibility/rigidity of the body. For example, if you shoot a ping pong ball against a slab of metal at the speed of sound, nothing would happen to the slab, but I'm guessing the ping pong ball would experience something drastic. Solids can experience more than a certain amount of shear without tearing apart, so it'll depend on the momentum of impact between the two bodies. – Kitchi Nov 25 '12 at 11:22