Inelastic Collisions of Two Spheres
In an elastic collision, both momentum and kinetic energy are conserved. However, in an inelastic collision (where the coefficient of restitution is smaller than 1) only momentum is conserved.
Snapshot 1: After a completely inelastic head-on collision both spheres move together.
Snapshot 2: In an elastic collision, the trajectories of two identical spheres in any angular collision are exactly perpendicular.
Snapshot 3: However, if the collision is inelastic the angle between the trajectories is smaller than 90°.
Snapshot 4: Here is the same collision as in snapshot 2, viewed in center-of mass frame.
Snapshot 5: The same collision as in snapshot 3, viewed in center-of mass frame.