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EnglandCombined ScienceSyllabus dot point

How is energy stored, transferred and conserved?

Energy stores and transfers, the conservation of energy, calculating kinetic and gravitational potential energy, and dissipation of energy to the surroundings.

A focused answer to Edexcel GCSE Combined Science Topic 3 (CP3), covering energy stores and transfers, the conservation of energy, calculating kinetic and gravitational potential energy, and how energy is dissipated to the surroundings.

Generated by Claude Opus 4.89 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this dot point is asking
  2. Energy stores and transfers
  3. Conservation of energy
  4. Calculating energy
  5. Dissipation of energy
  6. Try this

What this dot point is asking

Edexcel wants you to describe energy stores and the ways energy is transferred, state the principle of conservation of energy, calculate kinetic and gravitational potential energy, and explain how energy is dissipated to the surroundings.

Energy stores and transfers

Conservation of energy

For example, on a roller coaster, gravitational potential energy at the top is transferred to kinetic energy at the bottom; the total (ignoring friction) stays constant.

Calculating energy

Dissipation of energy

Whenever energy is transferred, some is dissipated (spread out) to the surroundings, usually as heat through friction or air resistance. This energy is not destroyed (energy is still conserved), but it becomes spread out and less useful, so it is described as wasted. Lubrication, streamlining and insulation reduce wasteful dissipation.

Thinking in terms of stores and transfers makes energy questions easier. For any change, ask which store is filling up and which is emptying, and which pathway is moving the energy. For a falling object, the gravitational potential store empties and the kinetic store fills, with the transfer happening mechanically through the force of gravity. For a kettle, the chemical (or electrical) supply empties and the thermal store of the water fills, with some energy dissipated to the room.

A closed system is one where no energy enters or leaves, so the total energy stays the same and can only be shifted between stores. A useful check is that, in a closed system, the total energy before equals the total energy after. So if a ball is dropped from a height and air resistance is ignored, the kinetic energy at the bottom equals the gravitational potential energy lost at the top. If air resistance is not ignored, the kinetic energy at the bottom is a little less, because some energy has been dissipated to the air as heat. Recognising where energy goes is what earns the marks in these questions.

Try this

Q1. State the principle of conservation of energy. [1 mark]

  • Cue. Energy cannot be created or destroyed, only transferred or stored.

Q2. Calculate the gravitational potential energy of a 2 kg2\,kg mass raised 3 m3\,m (g=10 N/kgg = 10\,N/kg). [2 marks]

  • Cue. GPE=mgh=2×10×3=60 JGPE = mgh = 2 \times 10 \times 3 = 60\,J.

Exam-style practice questions

Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

Edexcel 20194 marksA ball of mass 0.50 kg0.50\,\text{kg} is dropped from a height of 1.8 m1.8\,\text{m}. Calculate the gravitational potential energy it loses, and state its kinetic energy just before it hits the ground (assuming no air resistance). Use g=10 N/kgg = 10\,\text{N/kg}.
Show worked answer →

A 4-mark calculation using energy conservation.

Gravitational potential energy lost =mgh=0.50×10×1.8=9.0 J= mgh = 0.50 \times 10 \times 1.8 = 9.0\,\text{J} (2 marks). By conservation of energy, with no air resistance, all the gravitational potential energy is transferred to the kinetic store, so the kinetic energy just before impact is also 9.0 J9.0\,\text{J} (2 marks).

Markers reward the GPE calculation with units and the use of conservation of energy to give the kinetic energy equal to the GPE lost.

Edexcel 20213 marksA car is braking. Explain, using energy stores and transfers, what happens to the kinetic energy of the car, and why energy is described as dissipated.
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A 3-mark question on energy transfer and dissipation.

As the car brakes, friction between the brakes and the wheels transfers the kinetic energy of the car to the thermal energy store of the brakes and surroundings (so they heat up) (2 marks). The energy is described as dissipated because it spreads out to the surroundings as heat and becomes too spread out to be useful (it is wasted) (1 mark).

Markers reward the transfer of kinetic energy to a thermal store by friction, and the idea of dissipation as energy spreading out and becoming less useful.

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