As suspected, the coolest physics things in Second Life aren’t tagged, but are there. Here are some good things I found while trying to figure out shadow rendering in SL, which led to a lot of willy-nilly surfing on YouTube:

Particles in a SL box: http://www.youtube.com/watch?v=592rXlgCnoQ

Rollie-pollie planets: http://www.youtube.com/watch?v=90v2-doDuwA