Crumple Zones

Cars used to be designed to be robust in a crash and not to dent on impact but modern cars are designed to have a crumple zone that will 'concertina' in on impact - making the front or back of the car be damaged severely in even a slight 'bang'.

The reason why this is done is to protect the occupants of the car, rather than the car itself in a smash. Designers use their understanding of how to change the momentum of the vehicle by extending the time that the car takes to come to a halt and thereby decreasing the force experienced by the car and its occupants.

To stop the car has to experience an impulse.

Ft = impulse

Ft = Δp = mΔv

If a car had no crumple zone the impulse would have a shorter 't' component and a bigger 'F'. The damage to the car might not look as bad but the damage to the occupants would be much more serious!

Nowadays occupant safety is most important and even a small scrape can require replacement of car body parts - more expensive but safer!

Also see seat belts and air bags - they work on the same principle.

 Ft = impulse Ft = Δp = mΔv Always make it clear to the examiner that you understand that the safety feature does not 'reduce momentum'. That depends on the speed of the vehicle! Explain that it causes the time factor in the impulse to increase and that makes the force factor decrease.