Describe energy-store changes in everyday processes
Track what decreases and increases without assuming that one event involves only one store.
Section P1.7.1 · Energy
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Name the seven energy stores.
- Describe the initial and final states of a process.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which store is associated with an elastically compressed spring?
What you will learn
- Identify initial and final stores in a process.
- Include surroundings and intermediate stages when relevant.
Describe changes rather than relabel objects
When a toy is driven by an unwinding elastic spring, the spring's elastic strain store decreases and the moving toy's kinetic store can increase. Friction can also increase internal stores of the toy, track and surroundings. The spring has not become 'kinetic'; instead, energy has been transferred between stores belonging to the chosen system and its surroundings.
When a falling object loses height, its gravitational potential store decreases and its kinetic store can increase. If air resistance matters, some energy also transfers to internal stores and waves in the air. State whether the model neglects these other transfers before treating a decrease in one store as an equal increase in just one other store.
Less familiar stores still need a clear account
During a battery-powered lift, the battery's chemical store can decrease while the load–Earth gravitational potential store increases and the motor and surroundings gain internal energy. A charged capacitor can transfer energy electrically while its electrostatic store decreases. These are qualitative accounts: later electricity lessons address the circuits and quantitative relationships.
A nuclear process can decrease the available nuclear store and transfer energy that increases internal stores or is carried away by radiation. These examples do not call nuclear and chemical changes the same mechanism. A material's internal store can increase without a measured temperature rise, for example during melting; do not infer the energy account from temperature alone.
Sources for this lesson
Pause and explain
Must all energy leaving an unwinding spring become the toy's kinetic energy?
Worked example
Describe an unwinding spring toy that speeds up while its mechanism warms.
Show the worked solution
- The spring's elastic strain store decreases.
- The toy's kinetic store increases as it speeds up.
- Some energy also increases internal stores of the mechanism and surroundings.
Answer Elastic strain decreases; kinetic and internal stores increase.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Describe the stores changing when an elastic spring drives and warms a toy.
Give me a hint
Name the initial deformation store and both stated final effects.
Compare my reasoning
- Elastic strain energy decreases.
- The toy gains kinetic energy while speeding up.
- The warming mechanism gains internal energy.
Elastic strain decreases; kinetic and internal stores increase.
Look for these in your work
- Name the source store.
- Include both supplied outcomes.
Describe a battery lifting a load while its motor warms, and then a charged capacitor supplying a circuit.
Give me a hint
Use chemical and electrostatic sources for the two different processes.
Compare my reasoning
- The lift decreases the battery's chemical store.
- The load–Earth gravitational potential and motor internal stores increase.
- The capacitor's electrostatic store decreases as it transfers energy electrically.
Chemical → gravitational potential and internal; electrostatic decreases during electrical transfer.
Look for these in your work
- Keep the two sources distinct.
- Include the lift's internal-energy destination.
An object falls through air. A student claims every joule lost from gravitational potential becomes its kinetic energy. What model condition is missing?
Give me a hint
Ask whether other transfers, such as air resistance, are negligible.
Compare my reasoning
- A fall decreases the gravitational potential store.
- Air resistance can transfer energy to internal stores of the air and object and to waves.
- Equality with the kinetic increase alone needs those other transfers to be negligible.
Other transfers must be negligible; otherwise include internal stores and waves as well.
Look for these in your work
- Retain conservation.
- State the missing modelling condition.
Common mistakes
- Specify initial and final states.
- Include relevant surroundings.
- A store increase does not always imply a temperature rise.
What can you explain now?
Which store increases for a load lifted higher relative to Earth?
Compare with the explanation
The load–Earth gravitational potential store.
Its change depends on the relative height change, not just naming the load.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Describe a spring toy, a lift and a falling object using decreasing and increasing stores plus any required assumptions.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.