The Frog Blog has lots of useful reviews and links to recommended apps for teaching science. Including Touch Physics, of which it says:
“is a game where you must use your knowledge of the laws of physics to move a small wheel to a target star. Using your finger, you must draw boulders, levers, ramps and more to complete over 50 levels. It’s so addictive, but educational as well. I’ve certainly revised my law of the lever in preparation for this.”