Momentum

Momentum is a measure of how hard it is to stop a moving object.

Momentum = mass x velocity

p = mv

The units of momentum are kgm/s

Momentum is a vector. It has both size and direction

Force = change in momentum/time taken

The large the change in momentum of an object, the larger the force acting on it

The longer the contact time for the collision, the smaller the force acting on it. 

stopping distance = thinking distance + braking distance

thinking distance is the distance travelled between the driver seeing the hazard and pressing the brake

braking distance is the distance travelled between the brakes being pressed and coming to a stop

Thinking distance: alcohol/drugs, distractions, fatigue/tiredness

Stopping distance: condition of road (icy etc), condition of brakes, the speed of the vehicle