Answer the following question given this paragraph: 

For all collisions in a closed system, momentum is conserved. In some collisions in a closed system, kinetic energy is conserved. When both momentum and kinetic energy are conserved, the collision is called an elastic collision. Most collisions are inelastic because some amount of kinetic energy is converted to potential energy, usually by raising one of the objects higher (increasing gravitation PE) or by flexing the object. Any denting or other changing of shape by one of the objects will also be accompanied by a loss of kinetic energy. The only commonly seen elastic collisions are those between billiard balls or ball bearings, because these balls do not compress. And, of course, collisions between molecules are elastic if no damage is done to the molecules.


Q: When both momentum and kinetic energy are conserved in a closed system, the collision is called what?


A:
an elastic collision