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Acceleration (Edexcel IGCSE Physics (Modular))

Revision Note

Ashika

Written by: Ashika

Reviewed by: Caroline Carroll

Acceleration

Rate of change in velocity

  • Acceleration is defined as the rate of change in velocity

    • In other words, it describes how much an object's velocity changes every second

  • The equation below is used to calculate the average acceleration of an object:

acceleration space equals fraction numerator space change space in space velocity over denominator time space taken end fraction

a space equals space fraction numerator increment v over denominator t end fraction

  • Where:

    • a = acceleration in metres per second squared (m/s2)

    • increment v = change in velocity in metres per second (m/s)

    • t = time taken in seconds (s)

Formula triangle for acceleration, change in velocity and time

Acceleration Formula Triangle, downloadable IGCSE & GCSE Physics revision notes

To use an equation triangle, simply cover up the value you wish to calculate and the structure of the equation will be revealed

  • The change in velocity is found by the difference between the initial and final velocity:

change space in space velocity space equals space final space velocity space minus space initial space velocity

increment v space equals space v space minus space u

  • Where:

    • v = final velocity in metres per second (m/s)

    • u = initial velocity in metres per second (m/s)

  • Therefore, the acceleration, or the rate of change in velocity, equation can be written as:

a space equals space fraction numerator open parentheses v space minus space u close parentheses over denominator t end fraction

Speeding up and slowing down

  • An object that speeds up is accelerating

  • An object that slows down is decelerating

  • 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 (also known as deceleration)

Examples of acceleration and deceleration

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 50 m/s to 42 m/s 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:

Part (a)

Step 1: List the known quantities

  • Initial velocity, u space equals space 50 space straight m divided by straight s 

  • Final velocity, v space equals space 42 space straight m divided by straight s

Step 2: Write the relevant equation

increment v space equals space v space minus space u

Step 3: Substitute values for final and initial velocity

increment v space equals space 42 space minus space 50

increment v space equals space minus 8 space straight m divided by straight s

Part (b)

Step 1: List the known quantities

  • Change in velocity, increment v space equals space minus 8 space straight m divided by straight s 

  • Time taken, t space equals space 30 space straight s

Step 2: Write the relevant equation

a space equals space fraction numerator open parentheses v space minus space u close parentheses over denominator t end fraction space equals space fraction numerator increment v over denominator t end fraction

Step 3: Substitute the values for change in velocity and time

a space equals space fraction numerator negative 8 over denominator 30 end fraction

a space equals space minus 0.27 space straight m divided by straight s squared

Step 4: Interpret the value for deceleration

  • 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/s2

In other words, acceleration measures how much the velocity (in m/s) changes every second, m/s/s.

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    Previous:Core Practical: Investigating MotionNext:Velocity-Time Graphs
    Author
    Reviewer
    Ashika

    Author: Ashika

    Expertise: Physics Project Lead

    Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.

    Caroline Carroll

    Author: Caroline Carroll

    Expertise: Physics Subject Lead

    Caroline graduated from the University of Nottingham with a degree in Chemistry and Molecular Physics. She spent several years working as an Industrial Chemist in the automotive industry before retraining to teach. Caroline has over 12 years of experience teaching GCSE and A-level chemistry and physics. She is passionate about creating high-quality resources to help students achieve their full potential.