# The Moon orbits the Earth at a constant orbital speed. Explain why the Moon is continuously accelerating even though its orbital speed does not change.

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

> The Moon travels in a nearly circular orbit around the Earth, completing one orbit approximately every 27 days. Its orbital speed remains roughly constant throughout its orbit.

## Mark scheme (4 marks)

1. Velocity is speed in a given direction, so velocity is a vector quantity (has both magnitude and direction)
2. The direction of the Moon's motion is continuously changing as it orbits
3. A change in direction means the velocity changes, and acceleration is the rate of change of velocity
4. There is a resultant (gravitational) force acting on the Moon towards the Earth, which causes this acceleration

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