It is finally time to start implementing a basic Physics Engine. By the end of this chapter we will have particles flying around the screen in a physically realistic way. Before we start implementing our physics simulation, let's take a minute to discuss what we will be simulating, the rigidbody.
A rigidbody is an object that does not change its shape, the object is rigid. Think about dropping a ball filled with air on the ground. At the point of impact the ball would squash, and then it would stretch as it bounces back up. This ball is not rigid; it changes shape (but not volume), which allows it to bounce. Now imagine a ball of solid steel being dropped. It would not change in shape or volume, but it would not bounce either.
Our object can bounce around because we can model the math behind what it would be like if they bounced, but really they will be rigid. Our simulated objects will never change shape as a result of a physical reaction.
A scene can have hundreds of thousands...
