Have some ping pong balls? Have some liquid nitrogen (LN2)? You've got yourself a party! Poke two holes in a ping pong ball - angle the holes so they kind of slant sideways. They should point the same direction relative to some axis (think of a hero engine here). Now, dunk the punctured ball in the LN2. Then remove the ball (with tongs, folks - this is super-cold stuff) and as it warms up, it should start spinning.
I didn't think of this demo - there are some pretty cool videos that demonstrate this elsewhere on the internet. But I'm the only person I know of who put the ping pong under blacklights (long wave UV) and suspended it in a stream of air. Think of it as my "value-added" contribution to edutainment...
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