Energy Stores and Systems

Energy is one of the most fundamental concepts in physics. In this lesson you will learn about the different energy stores recognised by AQA, the four transfer pathways, and how to describe changes within a system. This topic forms the foundation of the Energy chapter of the AQA GCSE Combined Science Trilogy specification (8464), Section 6.1.

What Is Energy?

Energy is a quantity measured in joules (J). It cannot be created or destroyed — only transferred between stores. This principle is known as the conservation of energy and applies to every physical process.

In the AQA specification you must describe energy using the language of stores and transfer pathways. Older terms such as "light energy" or "sound energy" are not accepted.

Exam Tip: AQA will penalise answers that use outdated language. Always say "energy is transferred from the kinetic store" rather than "kinetic energy is converted into heat energy." Use stores and pathways consistently.

The Eight Energy Stores

There are eight energy stores you need to know for AQA GCSE Combined Science (8464).

Energy Store	Description	Example
Kinetic	Energy of a moving object	A car travelling along a motorway
Internal (thermal)	Total kinetic and potential energy of the particles in an object	A hot cup of coffee
Gravitational potential	Energy of an object raised above the ground	A skier at the top of a slope
Elastic potential	Energy stored in a stretched or compressed object	A compressed spring in a toy
Chemical	Energy stored in chemical bonds	Food, batteries, fossil fuels
Magnetic	Energy due to the interaction of magnets or magnetic fields	Two repelling magnets held apart
Electrostatic	Energy due to the interaction of electric charges	A charged balloon near a wall
Nuclear	Energy stored in the nucleus of an atom	Uranium fuel rods in a reactor

Exam Tip: Memorise all eight stores. A common 2-mark question gives you a scenario and asks you to identify the relevant stores. Practise naming them until you can list all eight without hesitation.

Energy Transfer Pathways

Energy is transferred between stores by four main pathways.

Transfer Pathway	Description	Example
Mechanically	By a force acting on an object (doing work)	Pushing a box across the floor
Electrically	By charges moving through a circuit	A current flowing through a kettle element
By heating	Due to a temperature difference between objects	A hot radiator warming a room
By radiation	By electromagnetic waves (light, infrared, etc.)	The Sun warming the Earth

graph LR
    A["Energy Store A"] -->|"Mechanical / Electrical / Heating / Radiation"| B["Energy Store B"]
    B -->|"Some energy always dissipated"| C["Internal energy of surroundings"]
    style C fill:#ffcccc,stroke:#cc0000

Exam Tip: When describing a transfer, always state: (1) the starting store, (2) the pathway, and (3) the final store. For example: "Energy is transferred from the chemical store of the battery electrically to the kinetic store of the motor."

Systems

A system is a defined group of objects being considered. When a system changes, energy is transferred within it or between it and the surroundings.

Examples of Energy Changes in Systems

System	Change	Energy Transfer
Object projected upwards	Rises and slows	Kinetic store → gravitational potential store
Vehicle braking	Slows down	Kinetic store → internal (thermal) store of brakes
Boiling water on a hob	Water heats up	Chemical store of gas → internal store of water
Falling ball	Accelerates downward	Gravitational potential store → kinetic store

Closed Systems

A closed system is one where neither matter nor energy can enter or leave. In a closed system the total energy is constant — energy may transfer between stores but the overall amount does not change.

Exam Tip: If a question states the system is closed, you know total energy is conserved. You can equate the energy before with the energy after to set up equations.

Describing Energy Transfers — Structured Approach

Follow this five-step method in extended-response questions:

Identify the system — what objects are involved?
Identify the initial store(s) — where is energy at the start?
State the transfer pathway — how does energy move?
Identify the final store(s) — where does energy end up?
Mention dissipation — energy transferred to the internal store of the surroundings (wasted).

Worked Example

A battery-powered fan is switched on.

Step	Answer
System	Battery, motor, fan blades
Initial store	Chemical store (battery)
Pathway	Electrically (through the circuit), then mechanically (motor turns blades)
Useful final store	Kinetic store (fan blades and air)
Wasted energy	Internal (thermal) store of the motor (by heating); sound to surroundings (by radiation)

graph TD
    A["Chemical store\n(battery)"] -->|"Electrically"| B["Motor"]
    B -->|"Mechanically"| C["Kinetic store\n(fan blades)"]
    B -->|"By heating"| D["Internal store\n(motor & surroundings)"]
    B -->|"By radiation"| E["Sound to\nsurroundings"]
    style D fill:#ffcccc,stroke:#cc0000
    style E fill:#ffcccc,stroke:#cc0000

Common Mistakes

Mistake	Correction
Using "heat energy" or "light energy"	Use "internal (thermal) store" and "radiation pathway"
Saying energy is "used up"	Energy is transferred and dissipated, never destroyed
Forgetting dissipation	Always mention wasted energy to internal store of surroundings
Confusing stores with pathways	A store is where energy is held; a pathway is how it transfers

Summary

Energy is measured in joules (J) and is always conserved.
There are eight energy stores: kinetic, internal (thermal), gravitational potential, elastic potential, chemical, magnetic, electrostatic, and nuclear.
Energy is transferred by four pathways: mechanically, electrically, by heating, and by radiation.
A system is a group of objects; energy transfers occur when a system changes.
In a closed system the total energy is constant.
Always describe transfers using the correct AQA vocabulary: stores and pathways, not "forms of energy."
This topic is assessed in AQA GCSE Combined Science Trilogy (8464), Section 6.1.