Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
Explain, using examples, how in all system changes energy is dissipated so…
Full specification wording
Topic 8 – Energy – forces doing work: 8.10 Explain, using examples, how in all system changes energy is dissipated so that it is stored in less useful ways
Every change in a system moves energy between stores, and some of it always ends up spread into the surroundings as thermal energy, which is harder to use for further work.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 10 of 15
Study notes
From the checked teaching notes for this specification point.
The idea
Every change in a system moves energy between stores, and some of it always ends up spread into the surroundings as thermal energy, which is harder to use for further work. A falling ball transfers energy from its gravitational store to its kinetic store, but friction with the air and the impact warm the ball and the ground, so a little energy is dissipated into the thermal store of the surroundings. A car braking converts kinetic energy into heating the brakes and air. In each case the total energy is conserved, yet the dissipated portion is stored in a less useful way because it is spread thinly and cannot easily be recovered to do useful work. Recognise that dissipation happens in all system changes, not only obvious ones.
What earns the marks
- Identifies that energy is conserved overall while some is transferred to the thermal store of the surroundings.
- Explains that dissipated energy is stored in a less useful, more spread-out way that is hard to recover for useful work.
- Gives a valid example such as a falling ball or a braking car and traces the energy transfer through it.
- States that dissipation occurs in all system changes, not only in obvious cases of friction or heating.
Common mistakes and how to put them right
Claims that dissipated energy is destroyed.
Put it right by stating that total energy is conserved and the energy is spread to the surroundings.
Treats dissipated energy as equally useful as stored energy.
Put it right by explaining it is stored in a less useful, spread-out way.
Gives an example without tracing the energy transfer.
Put it right by naming the stores involved and the transfer to the surroundings.
Exam tips
- Name the energy stores at the start and end of the example, then identify where energy is dissipated.
- Use the phrase 'stored in a less useful way' and explain why it is hard to recover.
- Check that your example shows dissipation to the surroundings, not just a change of store within the object.
Try the lesson
The start of the Topic 8 – Energy – forces doing work: 8.10 Explain, using examples, how in all system changes energy is dissipated so that it is stored in less useful ways lesson, made from checked teaching notes for this specification point.
Have a go first
A book slides across a table and slows to a stop. Into which store has most of its kinetic energy been transferred?
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