An elastic collision is a collision in which there is no net loss in kinetic energy in the system as a result of the collision. Both momentum and kinetic energy are conserved quantities in elastic collisions.
Some collisions between atoms in gases are examples of perfectly elastic collisions. Collisions of rigid billiard balls or the balls in a Newton's cradle are examples of elastic collision.
An inelastic collision is a collision in which there is a loss of kinetic energy. While momentum of the system is conserved in an inelastic collision, kinetic energy is not.
A ball dropped from a height h above a surface typically bounces back to some height less than h, depending on how rigid the ball is. Such collisions are simply called inelastic collisions.
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