# Energy stores and transfers

Energy cannot be seen, but it sits in stores (kinetic, gravitational, thermal, chemical, elastic) and moves between them. It is measured in joules (J).

Physics (school) · Part 03: Energy, work and power · Card 1 of 8 · Last updated 2026-10-19

## Analogy

Money in different pockets: it moves between pockets, but the total stays the same.

## Example

**Kettle**

Electrical energy in.
Thermal energy in the water.
A little sound and heat
escape to the room.

## In practice

A phone battery holds energy in a chemical store. Using it moves energy to light, sound and heat.

## Practice

### Flashcards

- **What is the unit of energy?** The joule (J).

## Questions people ask

### What are the main energy stores?

The main stores are kinetic (moving), gravitational potential (height), elastic potential (stretched or squashed), chemical (food, fuel, batteries), thermal (heat in a material) and nuclear. Energy is always measured in joules, and it moves from one store to another when something happens.

### What is the unit of energy?

The joule (J). One joule is the energy needed to lift a small apple, about 1 N, upwards by 1 metre. Larger amounts use kilojoules (kJ, 1,000 J) or megajoules (MJ, 1,000,000 J). A food label usually shows energy in kJ.

## Related concepts

- [Conservation of energy](https://studyvisually.com/learn/science/physics-school/physics-school-part-3/physics-school-part-3-concept-2)
- [Kinetic energy](https://studyvisually.com/learn/science/physics-school/physics-school-part-3/physics-school-part-3-concept-3)
- [Gravitational potential energy](https://studyvisually.com/learn/science/physics-school/physics-school-part-3/physics-school-part-3-concept-4)
- [Work done](https://studyvisually.com/learn/science/physics-school/physics-school-part-3/physics-school-part-3-concept-5)

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