When two billiard balls collide the collision is nearly elastic. An elastic collision is one in which the kinetic energy of the system is conserved before and after impact. Therefore, for simplicity one can assume that for collisions involving billiard balls, the collision is perfectly elastic.

When two billiard balls collide which is always conserved?

When two objects collide, they interact during the collision and the elastic forces that arise upon contact of the two objects with each other provide the change in object's velocity and/or direction of motion. However, total momentum and masses of two objects are usually conserved in collisions.

What happens to two billiard balls that collide?

If the cue ball strikes a stationary billiard ball straight on, then the cue ball will stop moving after the collision. It will have transferred all of its kinetic energy to the other ball, which will move forward with the same velocity that the cue ball had before the collision.