# Explain why planets closer to the Sun travel at a greater orbital speed than planets that are further away from the Sun.

> Pearson Edexcel International GCSE Physics (4PH1) — 8.1 Motion in the universe · Explain · 4 marks

> The eight planets in our solar system all travel in slightly elliptical orbits around the Sun. Their orbital speeds differ depending on their distance from the Sun.

## Mark scheme (4 marks)

1. Orbital speed is inversely proportional to the orbital period (or: orbital speed = 2πr/T)
2. Planets closer to the Sun have a smaller orbital radius
3. Planets closer to the Sun also have a shorter orbital period
4. The decrease in orbital period is greater than the decrease in orbital radius, so the orbital speed is greater (or: the combined effect of smaller r and much smaller T results in a greater orbital speed)

## Key terms

- [orbital speed](https://www.gradenine.co.uk/glossary/orbital-speed)

## 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/explain-why-planets-closer-to-the-47c4955a) · Published by Druglandscape Ltd.