Energy stores and systems
In GCSE Physics we no longer talk about "types of energy" — we talk about energy stores and transfers between them. This is the modern way to think about energy: energy is never lost or destroyed (the principle of conservation of energy), it just moves from one store to another, sometimes through useful pathways and sometimes wastefully into thermal stores via friction or air resistance.
The eight energy stores
You need to recognise and use all eight named stores:
- Kinetic — anything moving has a kinetic energy store. A bullet, a runner, even an electron.
- Gravitational potential — a mass raised against gravity (a book on a shelf, a ball at the top of a hill).
- Elastic potential — a stretched, compressed or twisted elastic object (a spring, a stretched rubber band, a bow).
- Chemical — energy stored in the bonds between atoms (food, fuel, batteries).
- Thermal (internal) — the kinetic and potential energy of vibrating particles in a hot object.
- Magnetic — two magnets held apart, or a magnet near an iron object.
- Electrostatic — two electric charges held apart (a charged comb, a Van de Graaff dome).
- Nuclear — energy stored in the nucleus that is released by radioactive decay, fission or fusion.
The four ways energy is transferred
Stores fill and empty by transferring energy along pathways:
- Mechanically — by a force doing work on an object (pushing, pulling, lifting, stretching).
- Electrically — by a current flowing through a circuit doing work.
- By heating — when a temperature difference drives energy from a hot object to a cold one (conduction, convection, radiation).
- By radiation — light, sound, infrared and other waves carrying energy.
What is a "system"?
A system is just an object or a group of objects we choose to study. When we draw a system boundary we list which stores are filling and which are emptying. Example — kicking a ball:
Before: the runner has lots of chemical store; ball has very little kinetic store. After: runner has slightly less chemical, slightly more thermal (muscles warm). Ball has gained kinetic store. Surroundings have gained a little thermal store from sound and air drag.
The total energy in all stores (system + surroundings) before equals the total after — that is conservation of energy.
How to describe a transfer in an exam
Examiners want a sentence with the form:
"Energy is transferred from the [start] store to the [end] store by [pathway]."
For example: a coal-fired power station — "Chemical store of coal → thermal store of water → kinetic store of turbine → electrical pathway to the National Grid → kinetic store of an electric kettle."
Useful and wasted transfers
Most real transfers are not 100% useful. Friction, sound and air resistance always shift some energy to a thermal store of the surroundings, which then dissipates and cannot easily be recovered. We call those wasted transfers. The fraction that ends up where we wanted it is the efficiency of the device.
⚠Common mistakes
- Saying "kinetic energy" instead of "kinetic store". You'll lose marks at 9-tier.
- Forgetting that thermal energy in the surroundings counts in conservation.
- Confusing store (what holds energy) with pathway (how it moves).
- Calling sunlight a "store" — it isn't. Light is a radiation pathway; the energy ends up in a thermal store on absorption.
Use the language carefully and the rest of P1 falls into place.
AI-generated · claude-opus-4-7 · v3-deep-physics