# Explain why a book resting on a table remains stationary, using Newton's laws of motion. Include in your answer an identification of the action–reaction pair of forces acting in this situation.

> IB DP Physics Standard Level (2023 syllabus) — A.2 Forces and momentum · Explain · 4 marks

## Mark scheme (4 marks)

1. The weight of the book (gravitational force on the book by the Earth) acts downwards on the book.
2. The table exerts a normal contact (reaction) force on the book directed upwards, equal in magnitude to the book's weight.
3. Since the net/resultant force on the book is zero, by Newton's first law the book remains stationary (in equilibrium).
4. The Newton's third law action–reaction pair is: the Earth pulls the book downward (weight) AND the book pulls the Earth upward with an equal and opposite gravitational force — these two forces act on different objects.

## Key terms

- [action–reaction pair](https://www.gradenine.co.uk/glossary/action-reaction-pair)

## Related

- [Revision notes for IB DP Physics Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-a-book-resting-on-79239997) · Published by Druglandscape Ltd.