Energy (Years 7–11) — Science

Every time something moves, heats up, glows or grows, energy is being shifted from one place to another. Energy is what makes things happen — and the astonishing thing is that you can never make more of it or lose any. You can only move it around.

Why this matters: the idea that energy is always conserved is one of the most powerful rules in all of science. If you can track where the energy went, you can explain almost any physical event, from a falling ball to a lit torch.

A torch: chemical → electrical → light (and heat)

Energy lives in stores

Four everyday energy stores — like separate bank accounts.

Think of energy like money in different bank accounts. It never disappears — it just gets moved between accounts. Each "account" is an energy store:

Kinetic — held by anything that is moving (a running child, a thrown ball).
Gravitational potential — held by anything lifted up high (a book on a shelf, water at the top of a dam).
Elastic potential — held by anything stretched or squashed (a drawn bow, a compressed spring).
Chemical — locked inside fuel, food and batteries, ready to be released.

Transfers: moving energy between stores

A transfer is energy flowing from one store to another. Drop a ball and its gravitational store empties as its kinetic store fills — that is why it speeds up. Switch on a torch and chemical energy in the battery becomes electrical, then light.

Event	Store emptying	Store filling
Ball falling	Gravitational potential	Kinetic
Torch lit	Chemical (battery)	Light (and heat)
Catapult fired	Elastic potential	Kinetic

The rule that never breaks

As the ball falls, gravitational energy pours into kinetic — the total is unchanged.

The law of conservation of energy says energy cannot be created or destroyed, only transferred. Energy is measured in joules (J) — the same currency for every store, which is exactly why you can add it all up and check the total never changes.

Worked reasoning. A ball is dropped from a shelf. Ask: what is moving, and what is happening to its height? It is speeding up, so kinetic is increasing; it is falling, so gravitational potential is decreasing. The total (kinetic + gravitational) stays the same the whole way down — one store simply pours into the other. That is conservation of energy in a single event.

Common mix-up: people say energy is "used up" or "lost". It is not — when a torch battery goes flat, its chemical energy has been transferred to light and heat that spread into the room. The energy still exists; it has just become spread out and hard to use again.

Energy is not lost — it spreads out into useful light plus wasted heat (still 100 J).

Memory hook: "KG-EC" for the four stores — Kinetic, Gravitational, Elastic, Chemical. And the golden rule: energy is never made, never destroyed, only moved — counted in joules.