AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Energy transfers in a system: Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed.
The conservation of energy states that the total energy of a closed system stays constant: energy is not created and not destroyed, only transferred between stores or dissipated to the surroundings.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
The conservation of energy states that the total energy of a closed system stays constant: energy is not created and not destroyed, only transferred between stores or dissipated to the surroundings. Useful energy transfer is the energy delivered to the intended store, such as a motor transferring energy to a gravitational potential store. Dissipated energy spreads into less useful stores, often warming the surroundings by heating, and cannot easily be recovered. For example, a falling ball transfers energy from its gravitational potential store to its kinetic store, while friction and air resistance dissipate some energy to the thermal store of the surroundings. The total energy before and after the change is the same.
What earns the marks
- States that energy cannot be created or destroyed, so the total energy of a closed system is constant.
- Describes useful energy transfer as energy delivered to the intended store or device.
- Explains that energy can be stored in stores such as kinetic, gravitational potential, elastic potential, thermal, chemical and nuclear stores.
- Describes dissipation as energy spreading to the surroundings, often by heating, becoming less useful.
- Applies conservation of energy to a system, showing that energy input equals useful output plus dissipated energy.
Common mistakes and how to put them right
Saying energy is used up or lost.
Put it right by stating that energy is transferred or dissipated, not destroyed.
Treating dissipated energy as destroyed.
Put it right by explaining that it spreads to the surroundings and remains in the total energy account.
Confusing energy stores with energy transfers.
Put it right by naming the store, such as thermal, and the pathway, such as heating or mechanical work.
Exam tips
- Use the words transferred, stored and dissipated precisely rather than saying energy is lost.
- For a system question, list the energy stores before and after the change and account for any dissipated energy.
- Check that any energy account balances: input energy equals useful energy plus energy dissipated.
Try the lesson
The start of the Energy transfers in a system: Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed. lesson, made from checked teaching notes for this specification point.
Have a go first
A ball is dropped and falls towards the ground. Which statement describes the energy change as the ball falls?
Key words
Say what each word means before you turn the card.
Conservation of energy
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Useful energy and dissipation
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Energy stores and pathways
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Energy accounting in systems
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See every definition
- Conservation of energy
- Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed, so the total energy of a closed system stays constant.
- Useful energy and dissipation
- Useful energy transfer is energy delivered to the intended store, while dissipated energy spreads into less useful stores, often warming the surroundings by heating, and cannot easily be recovered.
- Energy stores and pathways
- Energy can be stored in stores such as kinetic, gravitational potential, elastic potential, thermal, chemical and nuclear stores, and transferred by pathways such as heating or mechanical work.
- Energy accounting in systems
- The total energy before and after a change is the same, so energy input equals useful output plus dissipated energy.
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