# A satellite orbits the Earth in a circular orbit. Although the gravitational force acting on the satellite is a non-contact force, it does not do work on the satellite, and the satellite maintains a constant orbital speed. Explain why the gravitational force does not change the satellite's speed, and explain what effect the gravitational force does have on the satellite's motion.

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

> Satellites used for weather monitoring orbit the Earth in circular orbits at a constant orbital speed. Gravity is the only force acting on such a satellite.

## Mark scheme (4 marks)

1. The gravitational force acts perpendicular to (at right angles to) the satellite's direction of motion / velocity
2. A force can only change speed if it has a component in the direction of motion / because there is no component of force in the direction of motion, the speed does not change
3. The gravitational force continuously changes the direction of the satellite's velocity / motion
4. Because velocity is a vector quantity and its direction is changing, the satellite is accelerating / the gravitational force causes a centripetal acceleration

## Key terms

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

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-satellite-orbits-the-earth-in-eadc5067) · Published by Druglandscape Ltd.