Vehicles and Car Safety

The force of an impact is given by

Impact force = Change in Kinetic Energy
                              Impact Distance

 

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

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 3^rd law of motion.

 

 

Push of tyre on road           Push of road on tyre