Energy can be transferred — Physical education, 11–13 years
Energy is not a substance kept in one place. It is a way to track what can make changes happen, and it can move between objects or change form.
The ability to cause change
A moving ball, a warm drink and a charged battery have energy in different forms. When energy is transferred, something changes: the ball moves another object, the drink warms the air or the battery makes a lamp glow. Energy is measured in joules.
Why track energy?
It is hard to follow every push, sound, heat loss and movement in a machine. Energy gives us a useful account: where it started, where it went and what form it took. This helps explain why no machine gives out more energy than it receives.
A falling book
A 2-kilogram book is held 3 metres above the floor. Its gravitational energy is about mass × gravity × height: 2 × 10 × 3 = 60 joules. As it falls, this energy becomes movement energy; when it stops, much becomes sound and heat.
Energy is not used up
People often say that a lamp or a person ‘uses up’ energy, because the original battery or food is no longer available. The energy has not vanished: it has spread into light, motion, sound and mostly heat. The useful part may be gone while energy remains.
Energy in homes
A kettle transfers electrical energy into heating, while a speaker transfers it into sound and a fan into movement. Labels showing kilowatt-hours help compare how much electricity appliances transfer. Choosing efficient appliances means more energy becomes useful output and less becomes unwanted heat.
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