# A ball is attached to a string and swung in a vertical circle at constant speed. Explain why the ball moves in a circular path rather than continuing in a straight line, and describe the direction of both the velocity and the resultant force acting on the ball at any point in its circular path.

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

## Mark scheme (5 marks)

1. Without a force the ball would continue in a straight line (Newton's first law / inertia)
2. The tension in the string provides a resultant force that acts towards the centre of the circle
3. This inward (centripetal) force continuously changes the direction of the ball, keeping it on a circular path
4. The velocity of the ball at any point is directed along the tangent to the circle at that point
5. The resultant force (centripetal force) is always directed towards the centre of the circle, perpendicular to the velocity

## Key terms

- [circular path](https://www.gradenine.co.uk/glossary/circular-path)
- [velocity](https://www.gradenine.co.uk/glossary/velocity)
- [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-ball-is-attached-to-a-57fc2333) · Published by Druglandscape Ltd.