I remember one of my first experiences with GMod was trying to learn how ropes and stuff worked, and I ended up somehow with one washing machine physics-froze in mid-air with another tethered to it whizzing around at an almost game-breaking speed...then I unfroze the first one. Death was instantaneous.
Taken the fuck out by a pair of washing machines traveling at like Mach 2. I was laughing for a good ten minutes.
One of the reasons I got GMod (Aside from the fact that it was like $1.50 or something) is that it has all sorts of gears and stuff for building mechanisms to physically simulate... But after trying to mess around with that, I think I'd be better off concentrating on trying to do that stuff in the real world. ;o