# Newton's third law

When object A pushes on object B, B pushes back on A with an equal force in the opposite direction.

Physics (school) · Part 02: Forces and Newton's laws · Card 5 of 8 · Last updated 2026-10-19

## Analogy

Push a wall while on roller skates and you roll backwards.

## In practice

A rocket pushes gas down and backwards, and the gas pushes the rocket up and forwards.

## Practice

### Flashcards

- **What is Newton's third law?** When A pushes B, B pushes A with an equal force in the opposite direction.

## Questions people ask

### If forces come in equal pairs, why does anything move?

The two forces in a pair act on different objects, so they cannot cancel each other. A horse pulls a cart and the cart pulls back on the horse equally. The cart still moves because the horse also pushes the ground, and the ground pushes the horse forward.

### Is the weight of a book and the table's push on it a third law pair?

No. They happen to be equal and opposite when the book is still, but they act on the same object. A true pair acts on two different objects. The real pair for the book's weight is the book pulling the Earth upwards with an equal force.

## Related concepts

- [Newton's first law](https://studyvisually.com/learn/science/physics-school/physics-school-part-2/physics-school-part-2-concept-3)
- [Newton's second law](https://studyvisually.com/learn/science/physics-school/physics-school-part-2/physics-school-part-2-concept-4)
- [Force](https://studyvisually.com/learn/science/physics-school/physics-school-part-2/physics-school-part-2-concept-1)
- [Resultant force](https://studyvisually.com/learn/science/physics-school/physics-school-part-2/physics-school-part-2-concept-2)

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