Momentum

Momentum = mass x velocity
simplified: P = m x v
Units: Kg m/s

Ft = mv - mu
Ft is the impulse and is measured in NS

Conservation of momentum:
total momentum before collision = total momentum after collision

Crumple zones
Cars are designed so that, in case of impact, the front and back of the car "crumple" gradually. This links with Impulse because they increase the time it takes for the car to come to a stop and therefore reduce the force that is experienced by passengers.