Speed of ball. These four functions increment or decrement x or y. This function reverses y-axis ball movement. This function causes ball to move. One ball gains speed, the other loses speed.
All balls have the same radius.
If two Green balls collide, both bounce back. If two Red balls collide, both bounce back. If two Blue balls collide, both bounce back. If Green and Red balls collide, both bounce back. If Green and Blue balls collide, both bounce back.