IGCSEScienceCambridge (CIE)Combined SciencePhysicsRevision Notes1. Motion, Forces & EnergyMotionAcceleration

Acceleration (Cambridge (CIE) IGCSE Combined Science): Revision Note

Exam code: 0653

Leander Oates

Written by: Leander Oates

Reviewed by: Caroline Carroll

Updated on

Cambridge (CIE) Combined Science: PhysicsCambridge (CIE) Co-ordinated Sciences (Double Award): Physics

Acceleration

  • An object can change its speed by:

    • speeding up

    • slowing down

  • When an object speeds up, it is accelerating

  • When an object slows down, it is decelerating

Calculating acceleration

Extended Tier Only

  • When an object moves in a straight line, its acceleration can be defined as:

The change in speed per unit time

  • In other words, acceleration is the rate of change of speed

  • The acceleration of an object often changes throughout an object's journey

  • Therefore, it is often useful to know the average acceleration

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

  • Where:

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

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

    • increment t = time taken in seconds (s)

Formula triangle for acceleration, change in speed and change in time

1-2-2-acceleration-triangle-cie-igcse-23-rn

To use a formula triangle, simply cover up the quantity you wish calculate and the structure of the equation is revealed

 Change in speed

  • The change in speed is the difference between the initial and final speed:

increment v space equals space v space minus space u

  • Where:

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

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

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

  • If an object speeds up, its acceleration is positive

  • If an object slows down, its acceleration is negative

  • Acceleration is positive if it is in the same direction as the motion of the object

Acceleration of different objects

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 speed of the train decreases from 50 m/s to 42 m/s in 30 seconds.

(a) Calculate the change in speed 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 speed, u space equals space 50 space straight m divided by straight s 

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

Step 2: Write the equation for change in speed

increment v space equals space v space minus space u

Step 3: Substitute values for final and initial speed

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

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

Step 2: Write the equation for acceleration

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

Step 3: Substitute the values for change in speed 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 speed (m/s) changes every second, so the units are metres per second per second (m/s/s).

You may see the term "velocity" also used to describe speed. Speed means how fast something is going (e.g. 5 m/s), whereas velocity means how fast something is going and in which direction (e.g 5 m/s in a north direction). You don't need to know about velocity for IGCSE GCSE Combined Science.

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    Author
    Reviewer
    Leander Oates

    Author: Leander Oates

    Expertise: Physics Content Creator

    Leander graduated with First-class honours in Science and Education from Sheffield Hallam University. She won the prestigious Lord Robert Winston Solomon Lipson Prize in recognition of her dedication to science and teaching excellence. After teaching and tutoring both science and maths students, Leander now brings this passion for helping young people reach their potential to her work at SME.

    Caroline Carroll

    Reviewer: Caroline Carroll

    Expertise: Physics & Chemistry 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.