You may interrupt the applet by clicking the Stop -button. The other controls are now available. If you click the Start- button, the balls begin to roll again, unless you have made a change to one of the parameters of the applet. In that case tha applet first fills the screen with new balls. This is also the case if you click the Restart -button, even if you didn't make any changes to the parameters.
All disks have equal thickness.
You can distinguish balls from disks by the highlighting spot that are drawn on balls. The difference between balls and disks is their mass, which is proportional to the ball's volume. For a three-dimensional ball the volume is proportional to the third power of the radius, while a disk's volume is proportional to the square of the radius. This affects the kinetic energy, hence the collision behaviour of the balls. The color of the balls is randomly chosen, but the user may select the Kinetic energy -option, in which case a ball's color reflects it's amount of kinetic energy.