## Momentum

Momentum is a property of an object with mass. It is a measure of its instantaneous kinetic energy and is a measure of how easy it is to change its velocity, i.e. to change its direction or speed it up/slow it down. The higher the momentum, the harder it is to stop.

## Momentum and Collisions

If two objects collide, the total momentum before the collision will be the same as the total momentum after a collision. Momentum is conserved. You might be asked to calculate velocities after a collision. Remember that velocity is a

**vector**! If two objects are travelling in opposite directions, one will have a**negative**momentum.## Momentum and Forces

We can rearrange Newton's second law to look at momentum and we find out that if you take a longer time to change momentum, ie. you slow down more gently, you need less of a force. This is important in accidents.

You might find the following Phet simulation useful: