If you've already worked on games before, you should be familiar with Box2D. It's a multiplatform physics library that is broadly used across the gaming community. You'll find it really easy to work with it and get nice-looking physics pretty quickly, but this doesn't mean you have to create another Angry Birds clone, hint hint.
The first step is to create the world that will be in charge of the physics simulation by following the given steps:
module ( "PhysicsManager", package.seeall ) function PhysicsManager:initialize ( layer )