Science · Physics foundations
Energy stores & transfers
Kinetic, thermal, chemical, elastic.
What is energy?
Energy is the ability to make things happen or change. We cannot see energy itself, but we see what it does. Energy exists in different stores and moves between them through transfers. Understanding energy stores helps us explain how the world works.
Kinetic energy store
Kinetic energy is the energy in moving objects. Faster objects have more kinetic energy than slower ones. Heavier objects have more kinetic energy than lighter ones moving at the same speed. A rolling ball or a flying aeroplane both have kinetic energy.
Thermal energy store
Thermal energy is stored in hot objects. The hotter something is, the more thermal energy it contains. Particles inside hot objects move faster than in cold objects. A cup of tea has more thermal energy than an ice cube.
Chemical energy store
Chemical energy is stored in substances like food, fuel, and batteries. The energy releases when chemical reactions happen. Our bodies get energy from food through chemical reactions. Petrol in cars and wood on a fire store chemical energy.
Elastic energy store
Elastic energy is stored in stretched or squashed objects that can return to their original shape. Springs, rubber bands, and trampolines store elastic energy when deformed. When released, this stored energy transfers to other stores, often kinetic.
Worked examples
1. A child stretches a catapult and fires a stone into the air. Describe the energy transfers.
- The child does work stretching the catapult, storing elastic energy.
- When released, elastic energy transfers to kinetic energy as the stone accelerates.
- As the stone rises, kinetic energy transfers to gravitational potential energy.
- Air resistance causes some energy to transfer to thermal energy in the surroundings.
2. Explain why a hot oven and a warm room have different amounts of thermal energy.
- The oven is at a much higher temperature than the room.
- Higher temperature means particles move faster and have more energy.
- Therefore the oven contains more thermal energy per kilogram than the room air.
- The oven transfers thermal energy to cooler surroundings until temperatures balance.
3. A cyclist eating a banana then riding faster. Identify the energy stores involved.
- The banana contains chemical energy stored in its molecules.
- Digestion releases this chemical energy in the cyclist's body.
- Muscles use the chemical energy to do work on the pedals.
- The bicycle and cyclist gain kinetic energy as they speed up.
Try it yourself
A compressed spring inside a toy car is released. The car rolls across the floor and stops. Describe the energy stores at three stages: compressed, rolling, stopped.
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