Phun – 2D Physics Sandbox
See this demo.
While it is playing, you may ask, “What is Phun? (pronounced like “fun”?)”. It is a playground where people can build things, following their creative mind, to learn about some physics concepts like restitution and friction. It’s a Master of Science thesis by a Computing Science student Emil Ernerfeldt at VRLab, Umeå University, Sweden.
The program is multiplatform and is best run at a decent computer with hardware graphics acceleration. Try it out.