Abstract: This article provides a proof that the non loss of kinetic energy is equivalent to the recovery coefficient e=1 in a fully elastic collision between three-dimensional rigid bodies. This article extended the applicability of previous results which obtained in collisions between particles, and collisions between particle and rigid body. This proof avoids the calculation of rotational energy of rigid bodies, and completes a simple proof by starting with impulse and work done.

Key words: Fully elastic collisions, rigid body, recovery coefficient