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Getting started: energy stores and transfers
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Energy is the idea that links all of physics. KS3 introduced energy stores and transfers; GCSE adds equations, but the ideas come first.
Energy stores
Energy is measured in joules (J). 1 kJ = 1000 J.
Stores include: kinetic (moving things), gravitational potential (raised objects), elastic potential (stretched or squashed objects), thermal (hot objects), chemical (fuels, food, batteries), magnetic, electrostatic and nuclear.
Stores include: kinetic (moving things), gravitational potential (raised objects), elastic potential (stretched or squashed objects), thermal (hot objects), chemical (fuels, food, batteries), magnetic, electrostatic and nuclear.
Transferring energy
Energy moves between stores in four main ways:
Mechanically: a force moves something.
Electrically: an electric current flows.
By heating: from a hotter object to a cooler one.
By radiation: for example light.
Example: a battery-powered fan. Energy goes from the chemical store of the battery, electrically, to the kinetic store of the blades.
Mechanically: a force moves something.
Electrically: an electric current flows.
By heating: from a hotter object to a cooler one.
By radiation: for example light.
Example: a battery-powered fan. Energy goes from the chemical store of the battery, electrically, to the kinetic store of the blades.
Conservation and waste
Energy cannot be created or destroyed, only transferred. This is the conservation of energy.
total energy in = useful energy out + wasted energy
Wasted energy is usually dissipated (spread out) into the thermal store of the surroundings, warming them slightly.
total energy in = useful energy out + wasted energy
Wasted energy is usually dissipated (spread out) into the thermal store of the surroundings, warming them slightly.
A kettle is supplied with 2000 J of energy. 1700 J goes to the thermal store of the water. How much energy is wasted?
- Wasted = total in − useful
- = 2000 − 1700
Answer: 300 J
Energy is stored in stores and transferred mechanically, electrically, by heating or by radiation. It is never created or destroyed; wasted energy usually ends up heating the surroundings.
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