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Forces and Motion

The Change in Momentum and Car Safety.

How do Crumple Zones, Seatbelts and Airbags work?

The previous two pages show that
a car that crashes experiences a much larger force
than a car that has stopped safely by braking.
People (the driver and passengers) inside a car that crashes
are also exposed to a large force and this can cause injuries.

Below are listed three ways in which safety features
try to minimize the force during a crash by making
the change in momentum happen over a longer period of time
(cycle and motorcycle helmets work in the same way).


What is a Crumple Zone?

The car is designed so that the structure of the car
will give way during a collision. The
metal of the car will dent, bend and fold during a collision
which increases the amount of time it takes the car to stop.
The parts of the car that do this
(the front and the back) are called crumple zones.


How do Seatbelts work?

Car seatbelts protect people in two ways during a crash.
The seatbelt prevents the person being thrown about in the car,
possibly through the windscreen
or hitting themselves on the steering wheel or other objects.
The seatbelt also stretches a little, while restraining
the person during a crash. The stretching
increases the amount of time it takes the person to stop.


How do Airbags work?

Airbags are bags which inflate very quickly during a crash.
They provide a softer surface (like a pillow)
to prevent the people hitting themselves on hard objects.
They are designed to be used with a seatbelt.
An airbag will give way a little when a person hits it and this gives an
extra increase to the amount of time it takes the person to stop.

Bubble wrap packaging has the same effect
and is used to protect objects that are being transported.

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