# Explain how the restoring force acting on an object undergoing simple harmonic motion (SHM) gives rise to the periodic nature of the motion.

> IB DP Physics Standard Level (2023 syllabus) — C.1 Simple harmonic motion · Explain · 4 marks

> A small object is attached to a horizontal spring on a frictionless surface and displaced from its equilibrium position before being released.

## Mark scheme (4 marks)

1. The restoring force is always directed towards the equilibrium position (opposite to the displacement).
2. The magnitude of the restoring force (and therefore the acceleration) is proportional to the displacement from equilibrium.
3. The object accelerates towards equilibrium, overshoots (due to its inertia / velocity at equilibrium), and the restoring force then acts in the opposite direction again.
4. This process repeats continuously, producing periodic (oscillatory) motion about the equilibrium position.

## Key terms

- [restoring force](https://www.gradenine.co.uk/glossary/restoring-force)
- [simple harmonic motion (SHM)](https://www.gradenine.co.uk/glossary/simple-harmonic-motion-shm)

## Related

- [Revision notes for IB DP Physics Standard Level (2023 syllabus)](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/explain-how-the-restoring-force-acting-b58d0d18) · Published by Druglandscape Ltd.