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Press the button on a torch and the battery lights the bulb; nudge a book off a shelf and it gathers speed as it drops; pull back an elastic band and you can feel it straining to fling a paper pellet. Behind every one of these everyday moments lies a single idea: energy is being moved from one place to another. Physicists capture this with two words — stores and transfers. Energy sits in stores, and it is shifted between them along pathways. What it never does is get "made" or "used up"; it is only ever passed from store to store. This first lesson of Topic P5 (Energy) in OCR Gateway Combined Science A introduces the energy stores, sets out the four ways energy can be transferred, and shows how to follow energy as it flows through a system.
By the end of this lesson you should be able to name the main energy stores, list the four transfer pathways, describe familiar changes as energy moving between stores, and explain why it is incorrect to say that energy is "used up".
This lesson is mostly AO1 (recalling the stores and pathways and understanding what "conservation" means), with AO2 when you describe a real change in terms of the correct stores and transfers.
An energy store is simply a description of where energy is being held at a particular moment. Different situations hold energy in different ways, and OCR Gateway Combined Science expects you to know the following stores:
| Energy store | Where the energy is held |
|---|---|
| Kinetic | in anything that is moving (more mass and more speed means more of it) |
| Gravitational potential | in an object that has been lifted up in a gravitational field |
| Elastic potential | in a stretched or squashed spring, band or other springy object |
| Thermal (internal) | in a warm object — the hotter it is, the more it holds |
| Chemical | in fuels, foods and batteries, ready to be released by reactions |
| Nuclear | in the nuclei of atoms, released in nuclear reactions |
| Magnetic | in magnets attracting or repelling one another |
| Electrostatic | in charged objects that attract or repel |
A helpful picture is to imagine each store as a bucket that can hold a certain amount of energy. When something happens, energy pours out of one bucket and into another, but the amount of energy held across all the buckets together never changes — it simply shifts around.
Exam Tip: Always give the proper store names. Write "the chemical store of the fuel" or "the kinetic store of the car" rather than casual phrases such as "movement energy" or "heat energy". Examiners look for exactly those store names, so phrases like "the gravitational potential store" pick up the marks.
Energy does not leap between stores by itself — it is carried along one of four transfer pathways. A pathway describes how the energy gets shifted:
So a store tells you where the energy is, and a pathway tells you how it is moving. The same event can sometimes be described using more than one pathway, and the real skill is matching the correct pathway to what is physically going on.
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[Light and thermal: bulb]
G[Sun] -->|by radiation| H[Thermal store of Earth]
Exam Tip: Memorise the four pathways as one 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. Never mix up the pathway (how) with the store (where).
The heart of this topic is describing an ordinary event as energy moving from one store to another along a pathway. Every time, you should state three things: which store loses energy, which store gains it, and the pathway used.
A book slides off a high shelf and drops to the floor. Describe the energy transfer.
Answer: as the book falls, energy is transferred mechanically from the gravitational potential store to the kinetic store of the book.
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 small desk fan runs on a battery. Describe the energy transfers as its blades spin.
Answer: energy passes from the chemical store of the battery, electrically to the motor, then mechanically to the kinetic store of the spinning blades and moving air.
Exam Tip: A dependable sentence frame is: "Energy is transferred [pathway] from the [store] of [object] to the [store] of [object]." Filling this in for the event described almost always earns the marks.
In everyday language we say energy is "used up" — a torch battery "runs out", petrol is "used up", we feel we have "run out of energy". In physics this is simply not what happens. Energy is never created or destroyed; it is only ever moved from one store to another. When a battery "goes flat", its chemical store has not vanished — that energy has been shifted into other stores (the thermal store of the surroundings, light radiated away, and so on). The energy still exists in full; it has just been spread out to places where we can no longer make use of it.
This is why physicists prefer to say energy is dissipated (spread out to the surroundings, usually as thermal energy) rather than "lost" or "used up". The grand total of energy is unchanged — it has merely moved to less useful stores. Getting this idea clear now makes conservation of energy, the subject of the next lesson, far easier to grasp.
Exam Tip: Never write that energy is "used up", "lost" or "made". The correct wording is that energy is transferred between stores, and dissipated (spread out, usually to thermal stores) when it ends up somewhere less useful. That wording itself scores marks.
Most real events are not a single transfer but a chain, where energy passes through several stores one after another. The skill examiners reward is following that chain carefully, naming each store and each pathway in the right order rather than jumping straight from the start to the finish. It helps to think of it as a relay: the energy is handed on from store to store, and at each hand-over you can name both the store it leaves and the store it arrives in.
Consider a coal-fired power station lighting a lamp in your home. The energy begins in the chemical store of the coal. Burning the coal transfers energy by heating to the thermal store of water, turning it to steam. The steam pushes a turbine, transferring energy mechanically to the kinetic store of the spinning turbine and generator. The generator transfers energy electrically along the wires to your home, where the lamp transfers it by radiation to the surroundings as light (and, unavoidably, some by heating as the lamp warms). That single everyday act — switching on a light — has moved energy through the chemical, thermal, kinetic and (briefly) electrical pathways before it finally leaves as light and heat. At every step the total energy is unchanged; it is only ever handed on.
The value of writing the chain out in full is that it forces you to keep the store (where) and the pathway (how) separate at each stage. A weak answer collapses the whole thing into "the coal's energy becomes electricity"; a strong answer names every store the energy sits in and every pathway it travels along. When a question is worth several marks, that step-by-step chain is exactly where the marks are hidden.
A wind-up torch is powered by turning a handle. Describe the chain of energy stores and transfers from your hand to the light given out.
Answer: energy passes from the chemical store of your muscles, mechanically to the generator, then electrically to the bulb, which finally transfers it by radiation as light (with some wasted by heating). No energy is created at any point — your hand simply keeps topping up the chain from the chemical store in your body.
Exam Tip: For a "describe the energy transfers" question worth 4 or more marks, expect a chain of at least two or three transfers. Write each one as a separate step, naming the store it leaves, the pathway, and the store it enters. Do not merge several transfers into a single vague sentence — you lose a mark for every stage you skip.
Students most often trip up because they treat the four pathways as if they were extra stores. "Heat energy" and "electrical energy" feel like things you can hold, but in the OCR framework heating and electrical are pathways — ways of moving energy — not places energy is held. A warm object holds a thermal (internal) store; the process that filled it was heating. A charged battery holds a chemical store; the process that empties it into a motor is the electrical pathway. Keeping the two columns of ideas apart is the single most reliable way to pick up marks in this topic.
| This is a STORE (where energy is held) | This is a PATHWAY (how energy is moved) |
|---|---|
| Kinetic, gravitational potential, elastic potential | Mechanically (a force does work) |
| Thermal (internal) | By heating (hot to cold) |
| Chemical, nuclear | Electrically (a current flows) |
| Magnetic, electrostatic | By radiation (waves, e.g. light) |
A quick test: if you can point to where the energy is sitting, you are naming a store; if you are describing what is happening to move it, you are naming a pathway. "The kinetic store of the car" is a place; "transferred mechanically by the engine" is a process. Get into the habit of writing both — the store and the pathway — in every description, and the marks follow.
A system is just the object, or the group of objects, you have decided to study. The word is useful because it lets you talk about the total energy of the things you actually care about.
When you describe energy changes, you usually choose a system and then trace how energy moves between the stores within it. The closed-system idea is the foundation of conservation of energy, which comes 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); a warm object holds a thermal (internal) store |
| "A pathway and a store are the same thing" | A store is where energy is; 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 |
| "A machine can create energy" | No machine makes energy; it can only transfer energy that is already there |
Question (6 marks): A diver climbs a ladder, stands on a high board, then dives into the 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 core idea — energy stored at the top becoming movement on the way down — is there, but the store names are loose ("energy stored up", "movement energy") and no pathways are named. To move up a band, use the proper store names (gravitational potential, kinetic) and state that the transfers happen mechanically because gravity is a force doing work.
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 (their legs are a force doing work) from the chemical store in their muscles to their gravitational potential store, which grows 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 passes 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. Every store is named correctly, the mechanical pathway and the force responsible are identified at each stage, the energy is traced from the chemical store right through to dissipation in the water, and the answer closes with the conservation principle — a complete, well-ordered response.
This content is aligned with OCR Gateway Combined Science A (J250), Topic P5 Energy. Refer to the official OCR specification for exact wording.