Add radius to all constructors.
Change return type of physics methods to void.
They don't need to return anything, they just need to change some values.
Add update().
Calls both physics functions and then draws the ball.
Change b.draw() to b.update().
We want to update the ball with every frame, not just draw it.
Change framerate to 100.
We'll be taking time steps of .01 of a second, so if we want it to be in real time, the framerate should be 100 frames per second.
Make physics and drawing functions private.
We should only call constructors and update() from outside classes.