iPhysics is a physics engine and comes with a bunch of levels/examples to play with.

Release notes:

This is mostly an update to help those with the flicker problems… There is now an “Compatibility mode” in the options screen, that make the engine slower, uglier and behave nicer with other apps… The flicker problem is a compatibility problem with other apps, so if you disable the other apps which may be interfering with iPhysics, you don’t need the compatibility mode… If you can’t disable it, or can’t find the app which is causing problems, now at least you can play…

http://iphysics.r4m0n.net/index.php?title=Latest_Updates