Energy is stored in different ways. The IGCSE Physics syllabus requires you to identify and describe these energy stores and explain how energy is transferred between them.
Energy stores
| Energy store | Description | Example |
|---|---|---|
| Kinetic | Energy of a moving object | A rolling ball |
| Gravitational potential | Energy due to height in a gravitational field | A book on a shelf |
| Chemical | Energy stored in chemical bonds | Food, fuel, batteries |
| Elastic (strain) | Energy stored in a stretched or compressed object | A compressed spring |
| Nuclear | Energy stored in atomic nuclei | Uranium fuel rods |
| Thermal (internal) | Energy related to the temperature of an object | A hot cup of tea |
| Electrostatic | Energy due to separated charges | A charged capacitor |
| Magnetic | Energy due to magnets or current-carrying conductors | An electromagnet |
Energy transfers
Energy moves between stores by four main pathways:
- Mechanical work (a force moves an object)
- Electrical work (charge flows through a component)
- Heating (energy transfers due to a temperature difference)
- Radiation (energy carried by waves such as light, infrared, sound)
Example: a ball thrown upward
Chemical energy (in muscles) transfers to kinetic energy of the ball. As the ball rises, kinetic energy transfers to gravitational potential energy. At the highest point, kinetic energy is zero and gravitational potential energy is at its maximum.
Common errors and how to correct them
Describing energy as “lost.” Energy is never created or destroyed. When energy seems to disappear (friction, air resistance), it has been transferred to the thermal energy store of the surroundings. Use “dissipated” or “transferred to thermal energy of the surroundings.”
Confusing energy stores with energy transfers. “Heat” is a transfer pathway, not an energy store. The store is “thermal energy” or “internal energy.”
How to apply this in an exam
Describe the energy change as a transfer between named stores, using the pathway where relevant. For example: “Kinetic energy is transferred to thermal energy of the brakes and surroundings by friction (mechanical work).”
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