Press R to RESET (removes all the balls) Holding down the 1,2 or 3 key can be fun! I've been reading a web based tutorials by a guy named Randy Gaul (http://tutsplus.com/authors/randy-gaul) on how to implement a Rigid Body Physics Engine... The upshot is... It's complex! *grin*. I have only begun to implement the basics: Supporting circles with basic Impulse resolution and overlapping object correction. No friction, rotation or torque :S And no non-circular bodies! :S