# The Earth orbits the Sun in a nearly circular orbit. Gravity is described as a non-contact force. Explain how gravity keeps the Earth in its circular orbit around the Sun, and why the Earth is said to be continuously accelerating even though its orbital speed remains constant.

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

> The Earth takes approximately 365 days to complete one orbit of the Sun at an average distance of approximately 150 million kilometres.

## Mark scheme (4 marks)

1. Gravity acts on the Earth at a distance / without physical contact (through a field) pulling it towards the Sun
2. This gravitational force acts as the resultant force that continuously changes the direction of the Earth's velocity
3. Acceleration is the rate of change of velocity, and velocity is a vector quantity with both magnitude and direction
4. Because the direction of the Earth's velocity is continuously changing, the velocity is continuously changing, so the Earth is continuously accelerating

## 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/the-earth-orbits-the-sun-in-5cd276bc) · Published by Druglandscape Ltd.