Help deciphering a bit101 experiment (extracting physics information)

In my short months working with flash, I’ve learned that I best absorb material if I tinker with existing code.

Basically here, I’d like to differentiate and separate the code pertaining to the actual physics of the ball hitting the drawn surface. In effect, get rid of the neat drawing function and instead adapt it to a pre-drawn movie clip surface.

Any kind of guidance would be greatly appreciated. =)