Conservation and Dissipation of Energy
Revise Conservation and Dissipation of Energy for GCSE Physics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Energy is always conserved, but some is dissipated to less useful stores such as heat and spreads out into the surroundings.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Energy can be transferred usefully, stored or dissipated, but it cannot be created or destroyed. This is the principle of conservation of energy.
In a closed system there is no net change in the total energy. But energy is often dissipated, meaning it is transferred to the surroundings in ways that are not useful, usually to thermal energy stores. Once dissipated it becomes spread out and much less useful.
Friction between moving parts is the main cause. Lubrication reduces friction so less energy is dissipated. Thermal energy loss from a building can be reduced by thicker walls and by using materials with lower thermal conductivity.
Revision notes
Conservation of energy
Energy cannot be created or destroyed. It can be transferred usefully, stored or dissipated.
In a closed system there is no net change in the total energy — the total before equals the total after, however the energy has moved between stores.
Dissipation
Dissipated energy is transferred to the surroundings in ways that are not useful, usually to thermal energy stores.
It becomes spread out and much less useful, which is why it is sometimes described as wasted — though it has not been destroyed.
Reducing unwanted transfers
Lubrication reduces friction between moving parts, so less energy is dissipated as thermal energy.
Streamlining reduces air resistance. In buildings, thicker walls and materials with lower thermal conductivity reduce the rate of energy transfer to the surroundings.
Key points
- Energy cannot be created or destroyed.
- Energy can be transferred, stored or dissipated.
- A closed system has no net change in total energy.
- Dissipated energy goes to thermal stores in the surroundings.
- Friction causes unwanted energy transfer.
- Lubrication reduces friction and dissipation.
Worked examples
Example 1
State the principle of conservation of energy. [2 marks]
Model answer
Energy cannot be created or destroyed (1 mark). It can only be transferred usefully, stored or dissipated (1 mark).
Example 2
Explain what is meant by dissipated energy. [2 marks]
Model answer
Dissipated energy is energy transferred to the surroundings in ways that are not useful (1 mark), usually to thermal energy stores where it becomes spread out and much less useful (1 mark).
Example 3
Explain how lubricating a machine reduces unwanted energy transfers. [2 marks]
Model answer
Lubrication reduces the friction between the moving parts (1 mark), so less energy is dissipated to the thermal energy store of the surroundings (1 mark).
Common mistakes
Saying energy is lost.
It is dissipated to the surroundings, not lost. It still exists.
Saying dissipated energy is destroyed.
It is transferred and spread out, becoming less useful but not disappearing.
Forgetting the closed system condition.
Conservation applies to the total energy in a closed system.
Saying lubrication removes friction entirely.
It reduces friction, it does not eliminate it.
Exam tips
- Use the word dissipated rather than lost.
- State that energy becomes spread out and less useful.
- Name friction as the cause of unwanted transfers.
- Link each reduction method to the transfer it reduces.
Key terms
- Conservation of energy
- The principle that energy cannot be created or destroyed.
- Dissipated
- Transferred to the surroundings and spread out.
- Closed system
- A system where no energy enters or leaves.
- Lubrication
- Reducing friction between moving parts.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.