Conservation of Momentum

The CONSERVATION OF MOMENTUM states that in a CLOSED SYSTEM, the total momentum BEFORE an event is equal to the total momentum AFTER the event.

As an example, lets look at a pool cue ball hitting another ball:

If we assume both balls are 1kg, we can show that TOTAL MOMENTUM is CONSERVED:

Here the white ball’s momentum DECREASES and the red ball’s momentum INCREASES.

This means the SPEED of the white ball DECREASES and the SPEED of the red ball INCREASES.

Sometimes, the collision causes the objects to JOIN TOGETHER after they come into contact with each other. In these examples, you treat the two objects as ONE and ADD their masses: