# Physics

## Forms of energy

• Energy exists in different forms such as: Light, Sound, Kinetic, Nuclear, Electrical, Gravitational Potential, Elastic Potential and Chemical.
• Energy can be transferred from one form into another.
• Any object above the ground has gravitational potential energy.
• A falling object transfers gravitational potential energy to kinetic energy.
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## Conservation of energy

• Energy cannot be created or destroyed, only transferred from one form to another, or from one place to another.
• The total amount of energy is always the same, this is called the conservation of energy and it applies to all energy transfers.
• For example:
• when an object falls, gravitational potential energy is transferred to kinetic energy.
• stretching an elastic band transfers chemical energy to elastic potential energy.
• in a solar cell, light energy is transferred to electrical energy.
• a swinging pendulum transfers energy from gravitational potential energy to kinetic energy and back again as it swings.
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## Useful energy

• Useful energy is energy in the place we want it and the form we need it.
• Wasted energy is energy that is not usefully transferred.
• Useful energy and wasted energy both end up being transferred to the surroundings, which then become warmer.
• As energy spreads out, it gets more difficult to use for further energy transfers.
• Energy is often wasted becuase of friction between the moving parts of a machine. Friction is sometimes useful such as in the brakes on a bicycle or a car.
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## Energy and efficiency

• Energy is measured in joules (J). This unit is used for all forms of energy.
• The efficiency of an appliance = useful energy transferred by the appliance

total energy supplied to the appliance

•  No machine can be more than 100% efficient and the less energy wasted, the more efficicent the machine.
• Measures to make machines more efficient include reducing: friction, air resistance, electrical resistance, noise due to vibrations.
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