Why does energy never disappear?
Energy can never be made from nothing, and it can never be destroyed. It only moves from place to place or changes form — and when it seems to vanish, it has usually turned into heat.
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Energy
What energy is, where it comes from and why it never disappears.
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What it is and why it matters — intuition first, little or no math.
What is electric power?
Electric power tells how fast a device uses electrical energy. It is measured in watts (W): a kettle uses thousands of watts, a small LED lamp only a few.
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What is energy?
Energy is what makes things happen. It lets things move, warm up, shine, make sounds and grow — and it never disappears, it only changes from one form into another.
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Numbers & formulas
How to calculate it, with formulas and worked examples.
How efficient is a heat pump?
The coefficient of performance (COP) tells how much heat a heat pump delivers for each unit of electricity it uses. A COP of 3.5 means 3.5 kilowatt-hours of heat from just 1 kilowatt-hour of electricity.
Numbers & formulasUnder the hood