For an elastic collision it is characteristic that the sum of the kinetic energies of the involved bodies is constant. After a perfectly inelastic collision, however, both bodies have the same velocity; the sum of their kinetic energies is reduced, compared with the initial value, because a part of it has changed into internal energy (warming up).

The animations of elastic and inelastic collisions below demonstrate how the two object behave in a collision, while the applet lets you experiment with various aspects of collisions such as velocities of the bodies involved and their masses. The applet also shows such aspects as kinetic energy and momentum. Note the total momentum of the involved bodies is conserved, regardless whether the collision is elastic or inelastic. The movement of the common center of gravity is not influenced by the collision process.