AQA Physics (8463) 4.1.2.1 · Model
Energy transfers in a system
Triple Science · Foundation tier
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A bouncing ball rises a little less after each bounce.
If you had to guess, where does the energy go?
Key words
- conservation of energy
- closed system
- dissipated
- wasted
Key knowledge
Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed.
In a closed system, there is no net change to the total energy.
Energy moves between stores, but the total stays the same.
For example, a swinging pendulum with no air resistance or friction at the pivot moves energy between its kinetic and gravitational potential stores. The total stays the same.
In all system changes, energy is dissipated, so that it is stored in less useful ways.
This energy is often described as wasted.
Useful and wasted energy
| Row | Useful | Wasted |
|---|---|---|
| Car engine | ||
| Filament lamp | ||
| Phone charging | ||
| Electric kettle |
- Lubrication: oil reduces friction between moving parts, so less energy is dissipated.
- Thermal insulation: has a low thermal conductivity, so it reduces the rate of energy transfer by conduction to the surroundings.
Wrong: Energy gets used up.
Right: Energy is transferred or dissipated. It cannot be destroyed.
Wrong: Wasted energy has disappeared.
Right: It is still there, stored in less useful ways in the surroundings.
Key fact
Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed. Dissipated energy is stored in less useful ways and is often described as wasted.
Each bounce transfers some energy to the thermal stores of the ball and the ground.
So each bounce leaves less energy for the next one.
- Describe: say what happens, with an example.
- Explain: say what happens and why.
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