When two object collide, they must lose part of their kinetic energy upon collision. Part of this energy must be turned into sound and played by the system.
Camera.zoom method should take a parameter of type Point and use that as the focal point of the zoom operation. The focal point would stay fixed after the zoom and defaults to the point in the center of the current camera view.
Static and kinetic friction forces should be applied to disks when they are in contact.
Static friction is applied in the opposite direction of the tangential component of the forces applied to a disk. Its magnitude is calculated from the equation Fs = us * N, in which "us" is the co-efficient of static friction and N is the normal force.
Kinetic friction is applied in the opposite direction of the tangential component of a disks' velocity. Its magnitude is calculated from Fk = uk * N., in which "uk" is the co-efficient of kinetic friction and N is the normal force.