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Acceleration (Edexcel GCSE Combined Science) : Revision Note

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Edexcel Combined Science: PhysicsEdexcel Physics

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Acceleration

  • Acceleration is defined as the rate of change of 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 space fraction numerator 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)

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

change in velocity = final velocity − initial 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)

  • The equation for acceleration can be rearranged with the help of a formula triangle as shown:

Acceleration Formula Triangle, downloadable IGCSE & GCSE Physics revision notes

Speeding Up & 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 (sometimes called 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 down the relevant equation

change in velocity = final velocity − initial 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 space equals space minus 8 space straight m divided by straight s

  • The velocity of the train decreases by 8 m/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 down the relevant equation

acceleration space equals space fraction numerator 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

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

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

Freefall

  • In the absence of air resistance, all objects fall with the same acceleration

  • This is called the acceleration due to gravity:

g = acceleration due to gravity = 10 m/s2

leaning-tower-of-pisa, IGCSE & GCSE Chemistry revision notes

In the absence of air resistance, Galileo discovered that all objects (near Earth's surface) fall with an acceleration of about 10 m/s2

  • This means that for every second an object falls, its velocity will increase by 10 m/s

Estimating Accelerations

  • The acceleration of an object is a measure of how quickly its velocity changes

  • A typical family car, for example, takes around 10 seconds to go from 0 m/s to 27 m/s (roughly 60 mph)

    • This is an acceleration of about 2.7 m/s2

  • The table below gives some other typical accelerations:

Typical Accelerations Table

Typical Accelerations, downloadable IGCSE & GCSE Physics revision notes

Examiner Tips and Tricks

You should be able to estimate the magnitude of everyday accelerations. Memorise the examples given in the table to develop a sense of the magnitude of different accelerating objects.

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    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.