Car Safety

Car Safety

When a car stops suddenly, the car and its occupants will all experience a force as they stop. It is this force that causes the damage.

The force experienced can be explained by Newton's 2nd Law:

Force = change in momentum/time taken

Remember, this can be rewritten as Force = mass x acceleration, so if we want to reduce the force experienced by a passenger in the car, we need to alter the rate of change of momentum.

There is not a lot that can be done to change the mass on impact, but car designers can alter the acceleration by finding ways of making the car stop more slowly. They have introduced various design features to achieve this:

• Crumple zones - increase the time taken for the car to stop
• Air bags - extend the time taken for the driver to come into contact with the interior of the car
• Seat belts - stretch under force so slow down the body over a longer period of time
• Rigid passenger cell - does not deform under force so stops the passenger being crushed

All of these result in very small changes to the time taken to stop; this reduces the rate of change of momentum and so lessens the force experienced by the passengers. However, their combined effect is enough to make cars much safer.