IBPhysicsDPSLRevision NotesSpace, Time & MotionKinematicsAcceleration

Acceleration (DP IB Physics: SL): Revision Note

Written by: Ashika

Reviewed by: Caroline Carroll

Updated on 2 July 2026

Acceleration

Acceleration is defined as:
The rate of change of velocity
Acceleration is a vector quantity and is measured in metres per second squared (m s^–2)
- It describes how much an object's velocity changes every second

The average acceleration of an object can be calculated using:

$a v e r a g e a c c e l e r a t i o n = \frac{c h a n g e i n v e l o c i t y}{t i m e t a k e n}$

$a = \frac{∆ v}{∆ t}$

Where:
- $a$ = average acceleration (m s^–2)
- $∆ v$ = change in velocity (m s^–1)
- $∆ t$ = total time taken (s)

The change in velocity is the difference between the initial and final velocity, as written below:

change in velocity = final velocity − initial velocity

$∆ v = (v - u)$

Equations linking displacement, velocity, and acceleration

Equation Definitions, downloadable AS & A Level Physics revision notes

Instantaneous Acceleration

The instantaneous acceleration is the acceleration of an object at any given point in time
This could be for an object with a constantly changing acceleration
- An object accelerating is shown by a curved line on a velocity-time graph

What is a negative acceleration called?

The acceleration of an object can be positive or negative, depending on whether the object is speeding up or slowing down
- If an object is speeding up, its acceleration is positive
- If an object is slowing down, its acceleration is negative (deceleration)

However, acceleration can also be negative if it is accelerating in the negative direction

Acceleration Examples, downloadable IGCSE & GCSE Physics revision notes

A rocket speeding up (accelerating) and a car slowing down (decelerating)

Worked Example

A Japanese bullet train decelerates at a constant rate in a straight line.

The velocity of the train decreases from an initial velocity of 50 m s^–1to a final velocity of 42 m s^–1 in 30 seconds.

(a) Calculate the change in velocity of the train.

(b) Calculate the deceleration of the train, and explain how your answer shows the train is slowing down.

Answer:

(a)

The change in velocity is equal to

$∆ v = v - u$

Where:
- Initial velocity, u = 50 m s^–1
- Final velocity, v = 42 m s^–1

$∆ v$ = 42 − 50 = −8 m s^–1

(b)

Acceleration is equal to

$a = \frac{∆ v}{∆ t}$

Where the time taken is Δt = 30 s

$a = \frac{- 8}{30} = - 0.27 m s^{- 2}$

The answer is negative, which indicates the train is slowing down

Examiner Tips and Tricks

Remember the units for acceleration are metres per second squared, m s^–2. In other words, acceleration measures how much the velocity (in m s^–1) changes every second, (m s^–1) s^–1

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

I would just like to say a massive thank you for putting together such a brilliant, easy to use website.I really think using this site helped me secure my top gradesin science and maths. You really did save my exams! Thank you.

Beth
IGCSE Student

This website is soooo useful and I can’t ever thank you enough for organising questions by topic like this. Furthermore, the name of the website could not have been more appropriate as it literally did SAVE MY EXAMS!

Fathima
A Level Student

Incredible! SO worth my money, the revision notes have everything I need to know and are so easy to understand. I actually enjoy revising! It makes me feel a lot more confident for my GCSEs in a few months.

Kate
GCSE Student

Absolutely brilliant, both my girls used it for A levels and GCSE. It's saves on paper copies, also beneficial exam questions ranked from easy to hard. It's removed a lot of stress from the exams.

Sameera
Parent

Just to say that your resources are the best I have seen and I have been teaching chemistry at different levels for about 40 years

Mark
Chemistry Teacher

Excellent