AQA · GCSE · Combined Science

    Course version: 8464 · Version from Sept 2018

    Acceleration: acceleration = change in velocitʸ

    This statement gives the relationship used to find average acceleration: acceleration equals change in velocity divided by time taken.

    Checked against the AQA 8464 specification (opens in a new tab) on .

    • Point 2 of 21

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    This statement gives the relationship used to find average acceleration: acceleration equals change in velocity divided by time taken. Change in velocity is final velocity minus initial velocity, so you must record both values and subtract in the correct order. Time is the duration over which that change happens. For example, a train slowing from 30 m/s to 10 m/s in 8 s has change in velocity = 10 m/s − 30 m/s = −20 m/s, so acceleration = −20 m/s ÷ 8 s = −2.5 m/s². The negative sign shows deceleration relative to the forward direction. The unit m/s² arises because velocity in m/s is divided by time in s. This calculation gives an average acceleration; if the acceleration varies, the value applies to the whole interval. Always include direction when interpreting the sign.

    What earns the marks

    • Identify the initial and final velocities and calculate change in velocity as final minus initial.
    • Divide the change in velocity by the time taken to obtain average acceleration.
    • Include the correct unit, m/s², and interpret a negative value as deceleration in the chosen positive direction.
    • Recognise that the equation gives an average acceleration over the time interval, not necessarily an instantaneous value.
    • Rearrange the relationship to find change in velocity or time when those quantities are required.

    Common mistakes and how to put them right

    • Using initial velocity minus final velocity.

      Put it right by using final velocity minus initial velocity.

    • Forgetting to convert units such as km/h to m/s before dividing.

      Put it right by converting all velocities to m/s first.

    • Omitting the unit or writing m/s instead of m/s².

      Put it right by checking that velocity divided by time gives m/s².

    Exam tips

    • Underline the initial and final velocities in the question before substituting to avoid reversing the subtraction.
    • Show the change in velocity calculation separately from the division so method marks are clear.
    • If the answer is negative, state that the object is decelerating or accelerating in the opposite direction to the chosen positive direction.

    Try the lesson

    The start of the Acceleration: acceleration = change in velocitʸ lesson, made from checked teaching notes for this specification point.

    Have a go first

    A drone speeds up from 3 m/s to 15 m/s in 4 s. What is the drone's acceleration?

    Listen

    This statement gives the relationship used to find average acceleration: acceleration equals change in velocity divided by time taken. Change in velocity is final velocity minus initial velocity, so you must record both values and subtract in the correct order. Time is the duration over which that change happens. For example, a train slowing from 30 m/s to 10 m/s in 8 s has change in velocity = 10 m/s − 30 m/s = −20 m/s, so acceleration = −20 m/s ÷ 8 s = −2.5 m/s². The negative sign shows deceleration relative to the forward direction. The unit m/s² arises because velocity in m/s is divided by time in s. This calculation gives an average acceleration; if the acceleration varies, the value applies to the whole interval. Always include direction when interpreting the sign. A strong answer earns marks for these points. Identify the initial and final velocities and calculate change in velocity as final minus initial. Divide the change in velocity by the time taken to obtain average acceleration. Include the correct unit, m/s², and interpret a negative value as deceleration in the chosen positive direction. Recognise that the equation gives an average acceleration over the time interval, not necessarily an instantaneous value. A common slip: Using initial velocity minus final velocity. Instead, using final velocity minus initial velocity. Exam tip: Underline the initial and final velocities in the question before substituting to avoid reversing the subtraction.

    See it

    A flowchart running from top to bottom. Two boxes, Initial velocity and Final velocity, both lead into a box reading Change in velocity = final velocity − initial velocity. That box and a separate box, Time taken, both lead into a box reading Divide change in velocity by time taken. This leads to a box reading Average acceleration. From Average acceleration two boxes branch off: one reads Unit m/s², the other reads Negative value means deceleration in chosen positive direction.
    It shows how initial and final velocity give the change in velocity, which is divided by time taken to give average acceleration, with its unit and the meaning of a negative value.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A flowchart running from top to bottom. Two boxes, Initial velocity and Final velocity, both lead into a box reading Change in velocity = final velocity − initial velocity. That box and a separate box, Time taken, both lead into a box reading Divide change in velocity by time taken. This leads to a box reading Average acceleration. From Average acceleration two boxes branch off: one reads Unit m/s², the other reads Negative value means deceleration in chosen positive direction.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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