# Constant-acceleration equations

Three formulas that link position, velocity, acceleration and time when acceleration does not change.

Physics (university) · Part 01: Motion and vectors · Card 4 of 8 · Last updated 2026-10-19

## Analogy

A toolkit for any motion with a steady push, like a car braking evenly.

## Example

**Braking distance**

v0 = 20 m/s, v = 0, a = -5 m/s^2
0 = 20^2 + 2(-5)d
d = 400 / 10 = 40 m

## In practice

Use v squared = v0 squared + 2 a d when time is not given.

## Practice

### Flashcards

- **Which equation links v, v0, a and displacement without time?** v^2 = v0^2 + 2 a d.

## Questions people ask

### When can I not use the constant-acceleration equations?

They only work when acceleration stays the same the whole time. A car that keeps changing how hard it accelerates breaks the rule. A falling stone near the ground works well. A skydiver slowed by growing air drag does not, so these formulas fail there.

### How do I choose which kinematic equation to use?

List what you know and what you want. Each equation leaves out one of the five quantities: displacement, initial velocity, final velocity, acceleration and time. Pick the one that skips the quantity you neither have nor need. That keeps the algebra short and the answer clean.

## Related concepts

- [Displacement](https://studyvisually.com/learn/science/physics-university/physics-university-part-1/physics-university-part-1-concept-1)
- [Velocity](https://studyvisually.com/learn/science/physics-university/physics-university-part-1/physics-university-part-1-concept-2)
- [Acceleration](https://studyvisually.com/learn/science/physics-university/physics-university-part-1/physics-university-part-1-concept-3)
- [Free fall](https://studyvisually.com/learn/science/physics-university/physics-university-part-1/physics-university-part-1-concept-5)

Web page: https://studyvisually.com/learn/science/physics-university/physics-university-part-1/physics-university-part-1-concept-4
Study this card in the app: https://studyvisually.com/app/learn?category=physics-university&card=physics-university-part-1-concept-4