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 = v2 / 2a



The role of the wheels



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.