On a billiards table there may be a few balls moving at the same time. We call the sum of the linear momenta of all of them linear momentum of a particle system. Observe the fact that, as linear momentum is a vector, when you carry out the sum of linear momenta you must sum them as vectors, not as simple numbers.

When a few balls collide, their individual momenta alter: some decelerate, others accelerate... However, what happens to the combined linear momentum of all the balls?

In the following visual we will try to find out the answer to this question.