IGCSEPhysics: Co-ordinated Sciences (Double Award)CIERevision Notes1. Motion, Forces & EnergyMotionAcceleration

Acceleration (CIE IGCSE Physics: Co-ordinated Sciences (Double Award))

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Acceleration

  • An object can change its velocity in several ways:
    • speeding up
    • slowing down
    • changing direction
  • Any change in an object's velocity is an acceleration

  • When an object speeds up, it is accelerating
  • When an object slows down, it is decelerating

Calculating acceleration

Extended tier only

  • Acceleration describes how the velocity of an object changes over time
  • Acceleration is defined as:

The rate of change of velocity 

  • In other words, acceleration is the change in velocity per unit time
  • The acceleration of an object is often changing throughout an object's journey
  • Therefore, is it 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 velocity in metres per second (m/s)
    • increment t = time taken in seconds (s)

Formula triangle for acceleration, change in velocity 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 velocity

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

increment v space equals space v space minus space u

  • Where:
    • increment v = change in velocity in metres per second (m/s)
    • v = final velocity in metres per second (m/s)
    • u = initial velocity 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 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 equation for change in velocity

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, 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 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 Tip

Remember, the units for acceleration are metres per second squared, m/s2. In other words, acceleration measures how much the velocity (m/s) changes every second, so the units are metres per second per second (m/s/s).

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    Leander

    Author: Leander

    Expertise: Physics

    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.