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Energy on the move

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The amount of 'kinetic energy' that all moving objects have depends on their speed and mass. When a car brakes the kinetic energy is changed into heat energy.

Most cars currently use non-renewable fossil fuels as their energy source. Electricity can be used for example in battery-powered and solar-powered cars.

# Kinetic energy

All moving objects have kinetic energy. The amount of kinetic energy they have depends on:

• speed
• mass

A person has more kinetic energy when running than walking.

If a car and a lorry are driving at the same speed on the motorway the lorry has more kinetic energy than the car.

## Equation - higher tier

kinetic energy = 1/2 x mass x speed2

### Example

Question

How much KE does a person of mass 50kg running at 3m/s have?

kinetic energy = 1/2 x mass x speed2

kinetic energy = 1/2 x 50 x 32

kinetic energy = 1/2 x 50 x 9

kinetic energy = 225J

## Kinetic energy and braking distance

When a car brakes, its kinetic energy is changed into heat energy.

Work done by brakes = loss in kinetic energy

If the speed of the car doubles, the kinetic energy and braking distance quadruple.

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