# Vehicles and Car Safety

The force of an impact is given by

It is possible to reduce the impact force by increasing the time:

· Bumpers ‘give way’ to increase the time of impact.

· Crumple zones increase the time by absorbing the energy. They
deform plastically on collision. Energy absorbed = Force x Distance (extension)

· Seatbelts also increase the time spreading the weight over a
large are decreasing the pressure.

· Air bags increase the impact time by also spreading the force
over a large area reducing the pressure.

Stopping distance = thinking distance + breaking distance

Thinking distance = velocity x time

The reaction time remains constant.

Breaking distance = v^{2} / 2a

### The role of the wheels

Accelerating

Decelerating

The engine provides a torque to the wheels and friction between the tyres
and the road act in the direction of travel, based on Newton’s 3rd
law of motion.

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Car Safety