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Distance, speed and acceleration – WJECSafety features in cars

The motion of an object can be predicted by analysing the forces that act on the object. Balanced forces have no effect, while unbalanced forces can lead to change in acceleration.

Part of Physics (Single Science)Forces, space and radioactivity

Safety features in cars

To protect drivers and passengers from serious injury in the event of a crash or other collision, cars have safety features built in:

  • air bags
  • inertia wheel safety belts

All of these prolong the time of impact, reducing the force on the occupants.

Using Newton’s Second Law the force on the car in a collision will be given by this formula.

\(\text{F}={\text{m.a}}={\text{m.}}\frac{\text{v - u}}{\text{t}}\)

The safety features won’t change the mass of the car or the starting and end speeds, but do increase the impact time t in the formula. As impact time increases, the force on the occupants gets less as you are dividing by a higher value.

Speed limits in areas where there are lots of pedestrians – such as schools – are lowered to 20 miles per hour, as the force and kinetic energy of a vehicle in an impact are much reduced. When the speed of a car doubles, the impact force will be doubled and the kinetic energy will be quadrupled, leading to the possibility of fatal collisions with pedestrians and drivers.

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