Physics 02 builds on Physics 01, by adding another force to those acting on the balls: repulsion.
The balls are all trying to get to your mouse. They are hindered by friction and elasticity, as they were in Physics 01. This time, they are also hindered by each other; each ball is repulsed by the other balls, so they can never sit still. They are all trying to get to the exact same place, but at the same time, they are trying to get away from each other.
I managed to add the repulsion part of the equation myself, without looking at any reference material. I'm quite pleased with myself, if you want to know the truth. It worked on the first try, even.
This time, you can set the friction, elasticity, and repulsion of the balls either globally or individually by selecting either "All balls" or an individual ball from the "Which Ball" list.
The larger the value of friction, the slower the balls will travel.
Elasticity needs to be between 1 and 1.6 to work well. The closer the value is to 1 (say, 1.01), the more elastic the balls are.
I think repulsion works best if it is between 5 and 50. Try different values and see the effects.
You can also see what this looks like with a lot of balls flying around at once. I like the way it looks with 10 balls, myself.