GCSE Physics Energy Stores & Transfers Notes
Every energy question comes down to which store energy starts in, which store it ends in and how it got there. Learn the stores and pathways and you can describe any transfer.
Key concepts
- The eight stores
- Kinetic, gravitational potential, elastic potential, chemical, thermal, nuclear, electrostatic and magnetic.
- The four pathways
- Mechanical (a force doing work), electrical (charge flowing), heating (temperature difference) and radiation (light or sound).
- Sankey diagram
- A flow diagram whose arrow widths are proportional to energy. The useful output branches off; the wasted energy (usually thermal) continues along the bottom.
- A falling object transfers energy from the gravitational store to the kinetic store mechanically.
- A battery-powered lamp transfers from the chemical store electrically, then by radiation and heating.
- Wasted energy is nearly always dissipated to the thermal store of the surroundings.
Worked example
Describe the energy transfer when a car brakes to a stop.
- 1Identify the starting store: energy is in the kinetic store of the moving car.
- 2Identify the pathway: friction between the brakes and wheels does work (heating pathway).
- 3Identify the ending store: energy is transferred to the thermal store of the brakes and surroundings.
- 4State the outcome: the car stops and the brakes get hot.
Answer: Kinetic store → thermal store of the brakes/surroundings, by heating (friction).
Common mistakes
✗ Naming a pathway (e.g. 'electrical') as if it were a store.
✓ Stores hold energy; pathways move it. Keep the two lists separate.
✗ Saying 'heat energy' or 'movement energy'.
✓ Use the correct store names: 'thermal store' and 'kinetic store'.
✗ Drawing Sankey arrows without scaling the widths.
✓ Arrow width must be proportional to the amount of energy.
Quick check
Try these, then reveal the answers.
Which store does a stretched spring have energy in?Reveal answer
The elastic potential store.
By which pathway does a kettle transfer energy to the water?Reveal answer
Heating.
On a Sankey diagram, what does the width of an arrow show?Reveal answer
The amount of energy transferred.
Exam tips
- Answer transfer questions in the form: 'from the … store to the … store by … '.
- Never write 'heat energy' — examiners want 'thermal store' and 'heating pathway'.
- For efficiency, useful output is the branch that goes up; wasted energy continues along the Sankey diagram.
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Frequently asked questions
What is the difference between an energy store and a pathway?+
A store is where energy is held (e.g. kinetic, thermal); a pathway is how energy moves between stores (mechanical, electrical, heating, radiation).
Why is a Sankey diagram useful?+
It shows at a glance how much energy is transferred usefully and how much is wasted, because the arrow widths are drawn to scale.
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