# 1.2 Using Energy

• Created by: Twins 1&2
• Created on: 16-06-13 11:01

## 2.1 Forms of Energy

Energy exists in different forms such as:

• Light
• Sound
• Kinetic
• Electrical
• Gravitational Potential
• Elastic Potential
• Chemical

Energy can be transferred from one place to another or from one form to another.

Any object above the ground has gravitational potential energy.

A falling object transfers gravitational potential energy into kinetic energy.

1 of 6

## 2.2 Conservation of energy

The law of conservation of energy states that energy may neither be created nor destroyed. Therefore the sum of all the energies in the system is a constant. Stretching an elastic band transfers chemical energy to elastic potential energy. Swinging pendulum transfers energy from gravitational potential energy to kinetic energy and back again as it swings.      PE = mgh <---Formula

2 of 6

## 2.2 Conservation of energy

PE = mgh <----- Formula

The mass of the ball = 10kg
The height, h = 0.2m
The acceleration due to gravity, g = 9.8 m/s^2
Substitute the values into the formula and you get:

PE = 19.6J (J = Joules, unit of energy)

3 of 6

## 2.3 Useful Energy

A machine is something that transfers energy from one form to another.

The energy we recieve consists of:

·         Useful energy - has been transferred to the place and form we want.

·         Wasted energy - has not been usefully transferred

Both useful and wasted energy will eventually be transferred to the surroundings, which will be heated up. Energy is often wasted due to friction although some friction is useful.

As energy spreads out it becomes more and more difficult to use for further energy transfers.

4 of 6

## 2.4 Energy and Efficiency

Energy is measured in Joules ( J ). This unit is used for all forms of energy.

The energy supplied to a machine is called the input energy.

Input energy = useful energy output + wasted energy

Efficiency = useful energy output  /  total energy input

Efficiency can be left as a fraction or multiplied by 100 to give a percentage.

The energy transfer through an appliance can be shown in a sankey diagram.

As efficiency is a ratio it does not need a unit.

5 of 6

6 of 6