Car Design and Safety

When brakes applied, work is done by reducing kinetic energy of a car when transferred into heat and sound energy (traditional braking systems).

Some electric or hybrid cars use regenerative braking systems where energy instead of just converting it to heat.

System driving vehicle ised to do majority of braking.

Instead of converting kinetic energy of vehicle into heat energy, brakes put motor into reverse.

Motor runs backwards so wheels slowed.

Motor acts as electric generator converting kinetic energy to electrical energy stored as chemical energy in vehicle battery.

Energy stored instead of wasted.

Cars designed to convert kinetic energy safely.

A car slowing down quickly will have lots of kinetic energy converted into other forms of energy quickly which is dangerous. Big change in momentum over short time so huge forces.

Usually car safety increase time over which momentum happens as to lessen force on passengers.

Crumple zones at front and back crumple so car's kinetic energy converted into other forms as car changes shape.Also increase impact time decreasing force produced by change in momentum.

Side impact bars are strong metal tibes fitted into car doors to direct kinetic energy of crash away from passengers towards crumple zones.

Seat belts stretch slightly increasing time for passenger to stop, reducing force on chest. Some kinetic energy absorbed by seat belt stretching.

Air bags slow down gradually and prevent hitting hard surfaces.

Size and design of a car determines power. More powerful engine transfers more energy from fuel per second, so faster top speed.

Cars designed to be aerodynamic - shaped so air flows easily and smoothly, reducing air resistance.

Cars reach top speed when resistive force equals driving force of engine. Less air resistance means higher speed before terminal velocity.

Aerodynamic cars have higher top speeds.