Conservation of Energy and Energy Transfers — AQA GCSE Physics
Energy cannot be created or destroyed, but it can be transferred and dissipated.
The law of conservation of energy
Energy cannot be created or destroyed, only transferred, stored or dissipated. The total energy in a closed system stays constant.
Useful and wasted energy
In any energy transfer:
- some energy is transferred usefully, and
- some energy is dissipated ("wasted") to the surroundings, usually as thermal energy.
The wasted energy still exists (energy is conserved), but it spreads out into the surroundings and becomes less useful.
Reducing wasted energy
Unwanted energy transfers can be reduced by:
- Lubrication — reduces friction between moving parts, so less energy is wasted as heat.
- Thermal insulation — reduces the rate of energy transfer by heating. The rate of heat loss through a wall depends on its thickness and the thermal conductivity of the material — thicker walls and lower conductivity reduce heat loss.
Worked idea
When a ball bounces, some kinetic energy is dissipated as heat and sound at each bounce, so it does not return to its original height — but the total energy is still conserved.
Exam tips
- State the conservation of energy law precisely.
- Identify where energy is transferred usefully and where it is dissipated (usually as heat).
- Lubrication reduces friction; insulation reduces heat loss.
- Heat loss depends on thickness and thermal conductivity.