http://www.gaffer.org/game-physics/integration-basics
http://www.gaffer.org/game-physics/fix-your-timestep
http://www.myphysicslab.com/
http://www.codeproject.com/cs/media/PolygonCollision.asp
http://files.slembcke.net/chipmunk/chipmunk-docs.html
http://www.box2d.org/
http://www.bulletphysics.com/
http://www.gphysics.com/
http://www.essentialmath.com/