# Supersonic pushing

1. Aug 5, 2006

### daniel_i_l

When you push one end of a pole the other end reacts (starts moving to) after the amount of time that it would take sound to travel to that side. So what happens when one end is pushed faster than the speed of sound?
Thanks.

2. Aug 6, 2006

### Meir Achuz

The speed of sound is with respect to the pole.
The stress pulse always moves with that speed in the rest frame of the pole, independently of how the struck end moves.

3. Aug 6, 2006

### Clausius2

If with "pushing faster" you mean that the strain velocity applied is faster than the speed of the sound in the medium, I would expect to see "sort of" shock wave in the solid. If $$t_o$$ is the characteristic time of strain and $$t_1=L/c$$ is the time of a travelling stress wave, I would expect to see for times $$t/t_o\sim O(1)$$ a bunch of stress waves stored at the compressed pushed end, and for $$t/t_o>>1$$ such that $$t/t_1\sim O(1)$$ the stress waves would reach the other end and the deformation is propagated collaborating in the bulk motion of the pole. That's the case of a supersonic deformation.

4. Aug 7, 2006

### LURCH

I know that in the case of supersonic fluids energy from a collision is transfered back upstream by EM. Perhaps something similar would happen in a solid?