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 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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