How do we describe energy as it moves between stores in a system?
Energy stores and systems: describing how energy is transferred between stores when a system changes, and the principle of conservation of energy.
A focused answer to AQA GCSE Physics 4.1.1, covering the eight energy stores, how energy is transferred between stores when a system changes, and the principle of conservation of energy.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
AQA wants you to describe a system as an object or group of objects, name the energy stores energy can be transferred to and from, and use the idea that energy is conserved: it is never created or destroyed, only shifted between stores or dissipated.
Energy stores
The store-and-pathway model is the way AQA wants you to talk about energy, replacing older phrases like "heat energy" or "movement energy". The advantage of the model is that it makes conservation of energy easy to track: you can follow the total amount of energy as it moves out of one store and into another, checking that the total is unchanged. Every change in the world can be described as energy moving between these stores along one or more pathways, and being precise about which is a store and which is a pathway is rewarded in the exam.
Energy is held in stores. AQA expects you to name and recognise these stores:
- Kinetic (a moving object)
- Thermal (a warm object)
- Chemical (fuel, food, batteries)
- Gravitational potential (a raised object)
- Elastic potential (a stretched or compressed spring)
- Electrostatic (separated charges)
- Magnetic (two magnets pushed together)
- Nuclear (the nucleus of an atom)
Systems and transfers
For example, a kettle transfers energy electrically to the thermal store of the water. A falling ball transfers energy from its gravitational potential store to its kinetic store. The distinction between a store and a pathway is heavily tested by AQA. A store is where energy is held (kinetic, thermal, chemical and so on), while a pathway is how energy gets from one store to another (mechanical working, electrical working, heating, radiation). Heating, for instance, is not a store: it is the pathway by which energy reaches the thermal store. Writing "heat energy" as if it were a store loses marks; the correct phrasing is "energy is transferred by heating to the thermal store".
Conservation of energy
Energy that is dissipated (often to the thermal store of the surroundings) is no longer useful, but it is not lost: the total energy stays the same.
Try this
Q1. State the principle of conservation of energy. [2 marks]
- Cue. Energy cannot be created or destroyed, only transferred between stores or dissipated.
Q2. A child slides down a slide. Name the main energy transfer. [2 marks]
- Cue. From the gravitational potential store to the kinetic store (with some to the thermal store by friction).
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20194 marksA ball is thrown vertically upwards and then falls back down. Using the idea of energy stores and conservation of energy, describe the energy transfers as the ball rises and as it falls. Ignore air resistance.Show worked answer →
As the ball rises, it slows down, so energy is transferred from its kinetic store to its gravitational potential store (1 mark); at the highest point the kinetic store is at a minimum and the gravitational potential store is at a maximum (1 mark). As the ball falls, energy is transferred back from the gravitational potential store to the kinetic store, so it speeds up (1 mark). Because air resistance is ignored, the system is closed and the total energy is conserved, so the ball returns to the thrower's hand with the same speed it left at (1 mark). Markers reward correct store names (not "movement energy"), the direction of transfer in each phase, and reference to conservation of energy.
AQA 20213 marksDefine what is meant by a closed system, and state the principle of conservation of energy as it applies to one.Show worked answer →
A closed system is an object or group of objects in which no energy is transferred in or out, only between the stores inside it (1 mark). The principle of conservation of energy states that energy cannot be created or destroyed (1 mark); it can only be transferred between stores or dissipated, so the total energy of a closed system stays the same and there is no net change (1 mark). Markers reward "no energy in or out" for the closed system and both halves of the conservation statement (cannot be created or destroyed, only transferred). A common error is to say energy is "lost", when it is only transferred or dissipated.
Related dot points
- Kinetic, gravitational potential and elastic potential energy: calculating each store and using conservation of energy to link them.
A focused answer to AQA GCSE Physics 4.1.1, covering the kinetic energy, gravitational potential energy and elastic potential energy equations and how conservation of energy links them in a transfer.
- Specific heat capacity: the energy needed to raise the temperature of a substance, the equation linking change in thermal energy to mass, specific heat capacity and temperature change, and the required practical.
A focused answer to AQA GCSE Physics 4.1.1, covering the meaning of specific heat capacity, the equation linking thermal energy, mass, specific heat capacity and temperature change, and the required practical to measure it.
- Power and efficiency: power as the rate of energy transfer, the power equations, useful versus wasted energy, the efficiency equation and ways to reduce unwanted transfers.
A focused answer to AQA GCSE Physics 4.1.2 and 4.1.3, covering power as the rate of energy transfer, the two power equations, useful and wasted energy, the efficiency equation and methods of reducing unwanted energy transfers.
- Energy resources: the main renewable and non-renewable resources, their uses for transport, heating and electricity, and the environmental and reliability trade-offs.
A focused answer to AQA GCSE Physics 4.1.3, covering the main renewable and non-renewable energy resources, how they are used for transport, heating and electricity generation, and the trade-offs in reliability, cost and environmental impact.
Sources & how we know this
- AQA GCSE Physics (8463) specification — AQA (2016)