# Newton's second law

Net force equals mass times acceleration (F = ma). The same push gives a small mass more acceleration.

Physics (university) · Part 02: Newton's laws and forces · Card 3 of 10 · Last updated 2026-10-19

## Analogy

Pushing an empty shopping trolley versus a full one.

## Example

**Car acceleration**

a = F / m
a = 3000 N / 1200 kg
a = 2.5 m/s^2

## In practice

A 1200 kg car with a 3000 N net force accelerates at 2.5 m/s squared.

## Practice

### Flashcards

- **What does Newton's second law say?** Net force equals mass times acceleration (F = ma).
- **What is the SI unit of force?** The newton (N), equal to 1 kg m/s^2.

### Interview questions

**Explain Newton's third law using a rocket in space.**

- Engine pushes gas backward
- Gas pushes rocket forward with equal force
- Forces act on different objects, so rocket accelerates

## Questions people ask

### Does your mass change on the Moon?

Mass is the amount of matter in an object, measured in kilograms, and it never changes. Weight is the gravitational force on that mass, measured in newtons. An astronaut keeps the same mass on the Moon but weighs about six times less there.

### Why does F = ma use net force?

Acceleration depends on the combined effect of all forces, not on any single one. If you push a box with 10 N but friction pulls back with 10 N, the box does not accelerate. Always add all the forces first, then divide by mass.

## Related concepts

- [Newton's third law](https://studyvisually.com/learn/science/physics-university/physics-university-part-2/physics-university-part-2-concept-4)
- [Newton's first law](https://studyvisually.com/learn/science/physics-university/physics-university-part-2/physics-university-part-2-concept-1)
- [Net force](https://studyvisually.com/learn/science/physics-university/physics-university-part-2/physics-university-part-2-concept-2)
- [Weight](https://studyvisually.com/learn/science/physics-university/physics-university-part-2/physics-university-part-2-concept-5)

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