Energy stores and systems
Energy stores
Energy is never made or used up. It is kept in and moves between them. AQA uses eight stores:
| Store | Example |
|---|---|
| A moving bike | |
| A book on a high shelf | |
| A stretched spring or a squashed sponge | |
| (internal) | A hot cup of tea |
| Chemical | Food, fuel and batteries |
| Magnetic | Two magnets pushed apart, north to north |
| Electrostatic | Two positive charges pushed close together |
| Nuclear | The nucleus of a uranium atom |
Key terms
Systems and energy transfers
A is the object, or group of objects, you are studying. When a system changes, energy moves from one store to another. Energy can be transferred in four ways:
- Mechanically – a force does work, such as a push or a pull.
- Electrically – a current flows, such as a battery driving a motor.
- By heating – from a hotter object to a cooler one.
- By radiation – waves carry it, such as light or infrared from the Sun.
In a , no energy gets in or out, so the total energy stays the same. Energy only moves between stores inside the system.
Key terms
Describing energy flows
To describe a change, say which store empties, which store fills and how the energy gets there.
A falling ball: the ball's store empties and its store fills. Gravity transfers the energy mechanically. A little goes to the store of the air because of air resistance.
A car braking: the car's kinetic store empties. Friction between the brake pads and the wheels transfers energy mechanically to the thermal store of the brakes, which then heat the surroundings.
A kettle boiling water: energy is transferred electrically from the mains to the thermal store of the heating element. The element then heats the water, filling the water's thermal store.
Common mistake
Don't say energy is "used up" or "lost". It is transferred to other stores, often the thermal store of the surroundings.