Sprinkle Islands is a great physics based game by Mediocre. It has a million plus downloads so far on Google's Play Store and the best part is, it's free. It's available for both Android and iPhone.
You drive around on a little red fire truck and put out fires that are all about the islands. The villagers that you have to save are called Titans.
You are given a tank of water and the less you use to put out fires the more points you get. There are also a lot of puzzles that you have to solve, by using a bit of physics.
The game comes with great graphics and the best part is that there are no annoying ads all over the screen. The only downside to it is that you get only eight levels to play and if you want to play more then you have to get the full paid version. For just 17mb I think it's worth a shot. You will definitely enjoy it although it's very short lived.