# A student sets up a simple pendulum and observes that it oscillates with a fixed period. The student then increases the amplitude of the pendulum's swing while keeping the length of the pendulum the same. Explain why the period of the pendulum does not change when the amplitude is increased, and describe what would happen to the period if the student instead doubled the length of the pendulum.

> AQA A-Level Physics (7408) — 3.6.1 Periodic Motion · Explain · 5 marks

## Mark scheme (5 marks)

1. For simple harmonic motion / a simple pendulum, the period is independent of amplitude
2. A larger amplitude means a greater restoring force acts on the pendulum (bob)
3. The greater restoring force causes a greater acceleration / the bob moves faster, exactly compensating for the longer distance travelled
4. Period increases when the length is doubled (the period does not stay the same / the period gets longer)
5. Period is proportional to the square root of the length, so doubling the length increases the period by a factor of √2 (approximately 1.41 times longer)

## Key terms

- [period](https://www.gradenine.co.uk/glossary/period)
- [amplitude](https://www.gradenine.co.uk/glossary/amplitude)

## Related

- [Revision notes for AQA A-Level Physics (7408)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" 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-student-sets-up-a-simple-602e5c15) · Published by Druglandscape Ltd.