They fill a plastic bottle with liquid nitrogen, screw the cap on, drop it in a bucket full of warm water, cover it with ping pong balls, and when the heated, expanding gas bursts the bottle, the balls go jumping all over the place...
If you scroll the video to 3:50, you can see that the bucket jumps in the air, seemingly at the same time as the ping pong balls. Of course the force of the explosion is not pushing it up, but down. So what exactly is making it rise over 1 m off the ground?
I can only think of two possible explanations:
- Elastic recoil from the material of the bucket. This seems pretty unlikely to me, as in my experience plastic buckets don't bounce much.
- Pressure difference: the explosion drives everything out of the bucket, leaving a partial vacuum behind, so the atmospheric pressure outside the bucket pushes it up before air rushes back in to equalize the pressure. This seems more likely, but I would had thought that there would have been a longer delay.
Am I leaving any other possible explanation? Anybody willing to tackle a back of the envelope calculation of the height or delay for either of these?