# Mars orbits the Sun in a nearly circular orbit. Gravity is a non-contact force that acts between the Sun and Mars. Explain why Mars travels in a circular orbit rather than moving in a straight line, and state the direction in which the gravitational force on Mars acts.

> Pearson Edexcel International GCSE Physics (4PH1) — 1.4 Astronomy · Explain · 4 marks

> Mars orbits the Sun at an average distance of approximately 228 million kilometres, completing one orbit every 687 Earth days.

## Mark scheme (4 marks)

1. Without a resultant force, Mars would travel in a straight line (Newton's First Law / constant velocity in a straight line).
2. The gravitational force acts towards the Sun (from Mars towards the Sun / centripetally inward).
3. The gravitational force continuously changes the direction of Mars's velocity.
4. Gravity acts at a distance / with no physical contact between Mars and the Sun, acting through a gravitational field.

## Key terms

- [non-contact force](https://www.gradenine.co.uk/glossary/non-contact-force)
- [gravitational force](https://www.gradenine.co.uk/glossary/gravitational-force)
- [circular orbit](https://www.gradenine.co.uk/glossary/circular-orbit)

## Related

- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](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/mars-orbits-the-sun-in-a-56e3eaa6) · Published by Druglandscape Ltd.