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Switch on a torch and chemical energy in the battery lights the bulb; let a ball drop and it speeds up as it falls; stretch a catapult and you can feel it ready to fling a stone. In every one of these everyday events, energy is being shifted from one place to another. Physicists describe what is happening using the idea of energy stores and energy transfers: energy is held in stores, and is moved between them along pathways. Crucially, energy is never "used up" or "made" — it is only ever moved from store to store. This lesson opens Topic P7 (Energy) of OCR Gateway Science A by naming the energy stores, describing the four ways energy can be transferred, and showing how to track energy as it moves through a system.
By the end of this lesson you should be able to name the energy stores, list the four transfer pathways, describe everyday changes in terms of energy moving between stores, and explain why it is wrong to say energy is "used up".
Energy can be stored in different ways. An energy store is a description of where energy is held at a given moment. OCR Gateway Science A expects you to recognise the following stores:
| Energy store | Where the energy is held |
|---|---|
| Kinetic | in any moving object (the faster and heavier it is, the more it has) |
| Gravitational potential | in an object raised up in a gravitational field (lifted above the ground) |
| Elastic potential | in a stretched or compressed spring, elastic band or other springy object |
| Thermal (internal) | in a warm object — the hotter it is, the more thermal energy it has |
| Chemical | in fuels, foods and batteries — released by chemical reactions |
| Nuclear | in the nuclei of atoms — released in nuclear reactions |
| Magnetic | in magnets that are attracting or repelling each other |
| Electrostatic | in charged objects that attract or repel one another |
It helps to picture a store as a "bucket" that can hold energy. When something happens, energy drains out of one bucket and into another. The total amount of energy in all the buckets together never changes — it just moves around.
Exam Tip: Use the proper store names. Write "the chemical store of the fuel" or "the kinetic store of the car", not loose phrases like "movement energy" or "heat energy". OCR rewards the correct store names, and a phrase like "the gravitational potential store" is exactly what examiners look for.
Energy does not jump between stores by magic — it is moved along one of four transfer pathways. A pathway describes how the energy is shifted:
So a store is where energy is, and a pathway is how it moves. The same change can sometimes be described using more than one pathway, but the key skill is matching the right pathway to what is physically happening.
graph LR
A[Chemical store of fuel] -->|burning: by heating| B[Thermal store of water]
C[Kinetic store of cyclist] -->|pedalling: mechanically| D[Kinetic store of bike]
E[Chemical store of battery] -->|current: electrically| F[Thermal & light: bulb]
G[Sun] -->|by radiation| H[Thermal store of Earth]
Exam Tip: Learn the four pathways as a set: mechanically (a force), electrically (a current), by heating, by radiation. If a force moves something, the pathway is mechanical; if a current flows, it is electrical. Don't confuse the pathway (how) with the store (where).
The real skill in this topic is describing an everyday event as energy moving from one store to another along a pathway. Always state: which store loses energy, which store gains it, and the pathway.
A ball is dropped from a height and falls to the ground. Describe the energy transfer.
Answer: as the ball falls, energy is transferred mechanically from the gravitational potential store to the kinetic store of the ball.
Describe the energy transfers when an electric kettle boils water.
Answer: energy is transferred electrically to the kettle's element, and then by heating from the element to the thermal store of the water (raising its temperature).
A child's toy car runs on a battery. Describe the energy transfers as the car drives along.
Answer: energy moves from the chemical store of the battery, electrically to the motor, then mechanically to the kinetic store of the moving car.
Exam Tip: A reliable sentence frame is: "Energy is transferred [pathway] from the [store] of [object] to the [store] of [object]." Filling this in for the event in the question almost always scores the marks.
A very common everyday phrase is that energy is "used up" — a torch battery "runs out", petrol is "used up", we "run out of energy". In physics this is not what happens. Energy is never created or destroyed; it is only ever shifted from one store to another. When a battery "goes flat", its chemical store has not vanished — that energy has been transferred to other stores (the thermal store of the surroundings, light radiated away, and so on). The energy still exists; it has simply been spread out to places where it is no longer useful to us.
This is why physicists talk about energy being dissipated (spread out to the surroundings, usually as thermal energy) rather than "lost" or "used up". The energy is still there in total — it has just moved to less useful stores. Keeping this idea straight now will make the conservation of energy (the next lesson) much easier to understand.
Exam Tip: Never write that energy is "used up", "lost" or "made". The correct language is that energy is transferred between stores, and dissipated (spread out, usually to thermal stores) when it ends up somewhere less useful. This wording is itself worth marks.
A system is just the object, or group of objects, you have chosen to study. It is a useful word because it lets you talk about the total energy of the things you care about.
When you are asked to describe energy changes, you will usually pick a system and then track how energy moves between the stores within it. The idea of a closed system is the foundation of the conservation of energy, which you will meet next.
| Misconception | The correct idea |
|---|---|
| "Energy gets used up and disappears" | Energy is only ever transferred between stores; the total never changes |
| "Heat is a type of energy store" | "Heating" is a pathway (how energy moves); the store of a warm object is the thermal (internal) store |
| "A pathway and a store are the same thing" | A store is where energy is held; a pathway is how it is transferred |
| "A flat battery has lost its energy" | The energy has been transferred and dissipated to the surroundings, not destroyed |
| "Movement energy and kinetic energy are different" | They are the same store — always use the proper name, kinetic |
| "Energy can be created by a machine" | No machine creates energy; it can only transfer energy that is already there |
Question (6 marks): A diver climbs a ladder, stands on a high diving board, then dives into the swimming pool below. Describe the energy stores and transfers involved, from climbing the ladder to entering the water.
Mid-band response: "Climbing up gives the diver energy. At the top they have lots of energy stored up. When they dive, this turns into movement energy and they go fast into the water."
Examiner-style commentary: The basic idea — energy stored at the top becoming movement on the way down — is present, but the store names are loose ("energy stored up", "movement energy") and no pathways are named. To climb a band, use the proper store names (gravitational potential, kinetic) and say the transfers happen mechanically by the force of gravity.
Stronger response: "As the diver climbs the ladder, their muscles do work and energy is transferred to the gravitational potential store of the diver. At the top, they have a large gravitational potential store. As they dive, this energy is transferred mechanically to their kinetic store, so they speed up as they fall. When they hit the water, energy is transferred to the water."
Examiner-style commentary: A clear answer with correct store names and the mechanical pathway on the way down. To reach the top band, name the chemical store the climbing energy comes from, state that gravity is the force doing the work, and describe what happens to the energy on entering the water (transferred to the thermal and kinetic stores of the water, and dissipated).
Top-band response: "As the diver climbs the ladder, energy is transferred mechanically (the legs are a force doing work) from the chemical store in the diver's muscles to the gravitational potential store of the diver, which increases as they rise. Standing on the board, the diver has a large gravitational potential store. As they dive, gravity (a force) does work, transferring energy mechanically from the gravitational potential store to the kinetic store, so the diver speeds up as they fall. On entering the pool, energy is transferred from the diver's kinetic store to the kinetic and thermal stores of the water (the splash and a slight warming), and is dissipated to the surroundings. Throughout, the total energy is conserved — it is only shifted between stores."
Examiner-style commentary: Full marks. It names every store correctly, identifies the mechanical pathway and the force responsible at each stage, traces the energy from the chemical store right through to dissipation in the water, and finishes with the conservation principle — a complete, well-sequenced answer.
This content is aligned with OCR Gateway Science A GCSE Physics (J249), Topic P7 Energy (energy stores and transfers; transfer pathways; energy is shifted between stores, not used up). Refer to the official OCR specification document for the exact wording.