# A stone is tied to a string and swung in a horizontal circle at constant speed. Explain why the stone is accelerating even though its speed does not change, and describe the direction of both the acceleration and the resultant force acting on the stone.

> Eduqas A-Level Physics — 1.5 Circular motion (A-Level only) · Explain · 5 marks

> A student swings a stone tied to a string in a horizontal circle above their head. The stone completes each circle at a steady, constant speed.

## Mark scheme (5 marks)

1. Velocity is a vector quantity, so it has both magnitude (speed) and direction
2. The direction of the stone's motion is constantly changing as it moves in a circle
3. Because velocity is changing (direction changes), the stone is accelerating
4. The acceleration is directed towards the centre of the circle
5. The resultant force (tension in the string) also acts towards the centre of the circle

## Key terms

- [acceleration](https://www.gradenine.co.uk/glossary/acceleration)
- [resultant force](https://www.gradenine.co.uk/glossary/resultant-force)

## Related

- [Revision notes for Eduqas A-Level Physics](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-stone-is-tied-to-a-c9d162c0) · Published by Druglandscape Ltd.