# A tennis ball is dropped from rest and falls vertically downwards towards the ground. As the ball falls, it accelerates at first but then reaches a constant speed called terminal velocity. Explain why the ball first accelerates and then reaches terminal velocity.

> Eduqas GCSE Physics — 4.2 Forces, accelerations and Newton's laws of motion · Explain · 4 marks

## Mark scheme (4 marks)

1. Weight (gravitational force) acts downward on the ball
2. Air resistance (drag) acts upward on the ball, opposing its motion
3. Initially weight is greater than air resistance, so there is a resultant force downward, causing acceleration
4. As speed increases, air resistance increases until it equals weight, so the resultant force is zero and the ball moves at constant (terminal) velocity

## Key terms

- [terminal velocity](https://www.gradenine.co.uk/glossary/terminal-velocity)

## Related

- [Revision notes for Eduqas GCSE Physics](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-tennis-ball-is-dropped-from-e6c5e4f9) · Published by Druglandscape Ltd.