A child sits on a swing and is pushed so that it oscillates freely. Describe the energy changes that occur during one complete oscillation of the swing, starting from the highest point on one side.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
At the highest point the swing has maximum gravitational potential energy and minimum kinetic energy.
As it moves downwards towards the equilibrium position, gravitational potential energy is converted into kinetic energy.
At the lowest point the kinetic energy is maximum and the gravitational potential energy is minimum.
As it rises to the opposite highest point, the kinetic energy is converted back into gravitational potential energy.
The total mechanical energy (kinetic + potential) remains constant throughout the oscillation (ignoring losses).
As it moves downwards towards the equilibrium position, gravitational potential energy is converted into kinetic energy.
At the lowest point the kinetic energy is maximum and the gravitational potential energy is minimum.
As it rises to the opposite highest point, the kinetic energy is converted back into gravitational potential energy.
The total mechanical energy (kinetic + potential) remains constant throughout the oscillation (ignoring losses).
Examiner tips
- Use the exact terms ‘gravitational potential energy’ and ‘kinetic energy’.
- Show the energy transfer direction (potential → kinetic → potential).
- Mention that total mechanical energy is conserved.
Common mistakes
- Confusing kinetic energy with potential energy at the highest point.
- Forgetting to state that total mechanical energy is constant.
Mark scheme (5 marks)
- At the highest point the swing has maximum gravitational potential energy (and zero/minimum kinetic energy)
- As the swing moves downward/toward the equilibrium position, gravitational potential energy is transferred to kinetic energy
- At the lowest/equilibrium point, kinetic energy is at a maximum (and gravitational potential energy is at a minimum/zero)
- As the swing moves upward toward the other highest point, kinetic energy is transferred back to gravitational potential energy
- The total mechanical energy (kinetic energy + gravitational potential energy) remains constant throughout the oscillation (assuming no energy lost to surroundings/no air resistance/no friction)
Key terms in this question
Related
- All AQA A-Level Physics (7408) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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