How do I implement physics in a tetromino/Tetris game.

Using this simple Tetris example as a base

http://www.scirra.com/arcade/puzzle/1259/tetris

I want to implement a small physics based tetromino game. The physics should only be enabled after a tile is fully positioned and the physics shouldn't be too extreme.

Is this possible, somehow? Are there any good examples out there?

EDIT: I think I got most of it.

Was easier than I thought. It's still a bit buggy, though. The tetrominos sometimes start stacking on the top of the screen, destroying each other before the actual impact with the ground.