# A pendulum swings back and forth in simple harmonic motion. Describe the energy changes that occur during one complete oscillation of the pendulum, starting from the moment it passes through its equilibrium position moving towards its maximum displacement.

> WJEC A-Level Physics (Wales) — 5.1 Simple harmonic motion · Describe · 5 marks

> A simple pendulum is released from rest at its maximum displacement and swings freely. It passes through its equilibrium (rest) position and continues to its maximum displacement on the other side, before returning.

## Mark scheme (5 marks)

1. At the equilibrium position, the pendulum has maximum kinetic energy
2. As the pendulum moves from equilibrium towards maximum displacement, kinetic energy decreases (is converted to gravitational potential energy)
3. At maximum displacement (amplitude), the pendulum has maximum gravitational potential energy and zero kinetic energy / it is momentarily stationary
4. As the pendulum swings back towards equilibrium, gravitational potential energy is converted back into kinetic energy
5. The total energy (kinetic + gravitational potential) remains constant throughout the oscillation (in the absence of energy losses / assuming no friction or air resistance)

## Key terms

- [simple harmonic motion](https://www.gradenine.co.uk/glossary/simple-harmonic-motion)
- [equilibrium position](https://www.gradenine.co.uk/glossary/equilibrium-position)
- [maximum displacement](https://www.gradenine.co.uk/glossary/maximum-displacement)

## Related

- [Revision notes for WJEC A-Level Physics (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-pendulum-swings-back-and-forth-b5361c1e) · Published by Druglandscape Ltd.