Here's a free software site at MIT Media Lab where they're using a
variation of the LOGO language to do simple physics, math, & bio
mass-action simulations (including waves in traffic, burning forests,
emergent behavior in insect populations, etc.)
Looks like fun, but I can't try 'em without a Macintosh.
It seems intended to simulate hundreds of interacting entities (water
molecules?, termites?)
Someone should write "solid object" software, then simulate visible
forces, sound waves, mechanical energy transmission, etc. I wonder if
melting/crystallization could be done?