You are viewing a free preview of this lesson.
Subscribe to unlock all 10 lessons in this course and every other course on LearningBro.
This lesson introduces the concept of energy stores and energy transfers, as required by the Edexcel GCSE Combined Science specification (1SC0). Understanding how energy is stored and moved between stores is the foundation of the entire energy topic.
Energy is a quantity measured in joules (J). It cannot be created or destroyed — only transferred from one store to another. This is the principle of conservation of energy.
Energy enables things to happen: heating a room, moving a car, lighting a lamp or powering a phone all require energy transfers.
Exam Tip: You will never be asked to define energy in a single sentence, but you must be able to describe energy in terms of stores and transfers. Avoid outdated language such as "forms of energy" — the specification uses stores and pathways.
The Edexcel specification recognises eight energy stores. You must know all of them and be able to give examples.
| Energy Store | Description | Example |
|---|---|---|
| Kinetic | Energy of a moving object | A car driving along a road |
| Gravitational potential | Energy of an object raised above the ground | A book on a high shelf |
| Elastic potential | Energy stored in a stretched or compressed object | A stretched rubber band |
| Thermal | Energy related to the temperature of an object | A hot cup of tea |
| Chemical | Energy stored in chemical bonds | Food, batteries, fossil fuels |
| Magnetic | Energy due to magnets attracting or repelling | Two repelling magnets held apart |
| Electrostatic | Energy due to charges attracting or repelling | A charged balloon near a wall |
| Nuclear | Energy stored in the nucleus of an atom | Uranium fuel in a nuclear reactor |
Energy moves between stores along four pathways (sometimes called transfer mechanisms).
| Pathway | How It Works | Example |
|---|---|---|
| Mechanically | A force moves an object (work done) | Pushing a trolley |
| Electrically | A current flows through a circuit | A lamp connected to a battery |
| By heating | Energy moves from a hotter region to a cooler one | A radiator warming a room |
| By radiation | Energy is transferred by waves (light, sound, infrared) | The Sun warming the Earth |
Exam Tip: In exam answers, always name both the stores involved and the pathway. For example: "Energy is transferred from the chemical store of the battery to the thermal store of the filament electrically, and then to the thermal store of the surroundings by radiation."
To describe an energy transfer fully you should state:
A ball is dropped from a height.
A battery-powered torch is switched on.
Energy transfers can be represented using simple flow diagrams. Arrows show the direction of transfer and can be labelled with the pathway.
flowchart LR
A["Chemical store\n(fuel)"] -->|Mechanically| B["Kinetic store\n(car)"]
B -->|By heating| C["Thermal store\n(surroundings)"]
A -->|By heating| C
A system is an object or group of objects that you are studying. When a system changes, energy is transferred. You define the boundary of the system depending on the question.
| System | Change | Transfer |
|---|---|---|
| A kettle and its water | Water is heated | Chemical store of electricity supply → thermal store of water |
| A ball and the Earth | Ball is thrown upward | Kinetic store → gravitational potential store |
| A spring and a trolley | Compressed spring released | Elastic potential store → kinetic store |
Exam Tip: When answering a question about a system, first identify which objects are inside the system and which are outside. Energy leaving the system is said to be dissipated to the surroundings.
| Misconception | Correction |
|---|---|
| "Energy is used up" | Energy is transferred, not used up. The total energy is always conserved. |
| "Heat is a store" | Heat is a pathway (by heating). The store is thermal. |
| "Light energy" | Light is a pathway (radiation). Energy is in the thermal or nuclear store of the source. |
| "Sound energy" | Sound is a transfer by mechanical waves. The energy ends up in the thermal store. |
Energy is measured in joules (J). Larger quantities use:
| Unit | Symbol | Equivalent |
|---|---|---|
| kilojoule | kJ | 1 kJ = 1 000 J |
| megajoule | MJ | 1 MJ = 1 000 000 J |
| gigajoule | GJ | 1 GJ = 1 × 10⁹ J |
A heater transfers 3.5 MJ of energy. Express this in joules.
3.5 MJ=3.5×106 J=3500000 J
A 600 kg roller-coaster car sits at the top of a 25 m drop and then descends to ground level. Ignoring friction, use GPE=mgh with g = 10 N/kg to estimate the energy transferred.
This single example touches on four stores (chemical of operator lift motor, gravitational potential, kinetic, thermal) and three pathways (electrically, mechanically, by heating) — a perfect template for full-mark six-mark questions.
A 2 kW electric kettle is switched on for 90 s to bring water from 20°C to near boiling.
An archer draws a bow, storing 60 J in the elastic potential store of the limbs. When released, 54 J is transferred to the kinetic store of the arrow and 6 J is dissipated to the thermal store of the bow and string.
One of the most common student errors is confusing a store with a pathway. The table below fixes the distinction in place.
| Word a pupil might write | Store or pathway? | Correct terminology |
|---|---|---|
| "Heat energy" | Neither — ambiguous | Thermal store, transfer by heating |
| "Light energy" | Pathway | Transfer by radiation |
| "Sound energy" | Pathway | Transfer mechanically (longitudinal waves) |
| "Electrical energy" | Pathway | Transfer electrically |
| "Movement energy" | Store | Kinetic store |
| "Height energy" | Store | Gravitational potential store |
| "Stretch energy" | Store | Elastic potential store |
Common mistake callout: Writing "heat energy" on its own is almost always marked wrong at GCSE. Examiners want to see either the thermal store or the pathway by heating.
The diagram below shows how energy flows in a petrol-powered car, with the width of each arrow (shown by the label) roughly proportional to the energy involved.
flowchart LR
A["Chemical store\n(petrol) 1000 J"] -->|"Mechanically — 250 J"| B["Kinetic store\n(car)"]
A -->|"By heating — 600 J"| C["Thermal store\n(engine block)"]
A -->|"By heating — 150 J"| D["Thermal store\n(exhaust gases)"]
B -->|"By heating\n(air resistance, tyres)"| E["Thermal store\n(surroundings)"]
Even without numerical widths, this Sankey-style layout tells the story: most of the chemical store of a fuel ends up in the thermal store of the surroundings. Only a fraction becomes the useful kinetic store of the car.
Callout — do not write "energy is lost". Energy is never lost. It is transferred or dissipated to the surroundings. Writing "lost" suggests a violation of conservation of energy and will be penalised.
Callout — avoid "gains" and "loses" as standalone verbs. Prefer "has its ... store increased/decreased" or "energy is transferred from the ... store to the ... store". This mirrors the Edexcel mark scheme.
Grade 3–4 response (foundation floor): "When a ball falls, gravity gives it kinetic energy. Some of it turns into heat because of air." — Correct ideas are present, but imprecise. The candidate conflates a store (kinetic) with an informal action ("gives") and calls heat a thing rather than a process.
Grade 5–6 response (solid pass): "Energy in the gravitational potential store of the ball is transferred to its kinetic store as it falls. A small amount is transferred to the thermal store of the air and the ball by heating because of air resistance." — All stores named precisely, pathway identified. No ambiguity between useful vs wasted energy.
Grade 7–9 response (top band): "The decrease in the gravitational potential store of the ball equals, by conservation of energy, the increase in its kinetic store plus any energy dissipated to the thermal store of the surroundings. In a vacuum, no energy would be dissipated, so the kinetic store at impact would equal the initial gravitational potential store. In air, a fraction is transferred by heating (air resistance) and a small fraction mechanically (as a sound wave), meaning the useful kinetic store is less than the total input. Describing the transfer distinguishes useful from wasted energy and supports the principle that total energy is conserved." — Correct vocabulary (gravitational potential, kinetic, thermal, dissipated, useful vs wasted), a quantitative link and a conservation statement.
The progression from Grade 3–4 to Grade 7–9 is one of precision: the same physics, but each store and pathway is named correctly and the principle of conservation is made explicit.
Edexcel alignment: This content is aligned with Edexcel GCSE Combined Science (1SC0) Physics Topic 3 Conservation of energy — specifically CP3 Energy stores and systems, CP4 Energy changes in systems and CP5 Conservation and dissipation of energy. Assessed on Physics Paper 1.