AQA · GCSE · Combined Science

    Course version: 8464 · Version from Sept 2018

    Speed: speed, v, in metres per second, m/s

    Speed, v, is the rate of change of distance with time, measured in metres per second (m/s).

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

    • Point 16 of 18
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Speed, v, is the rate of change of distance with time, measured in metres per second (m/s). It is a scalar quantity, so direction is not specified. You calculate average speed using v = s / t, where s is distance in metres and t is time in seconds. For example, a runner who covers 400 m in 50 s has an average speed of 400 / 50 = 8 m/s. On a distance-time graph, speed is the gradient of the line. You must be able to convert units such as km/h to m/s, substitute correctly into the equation, and interpret the result. Always include the unit m/s and consider whether the value is realistic.

    What earns the marks

    • Speed is the distance travelled per unit time and is a scalar quantity, so direction is not required.
    • The SI unit of speed is metres per second, symbol m/s; other units such as km/h must be converted before substitution.
    • Average speed is calculated using v = s / t, where s is distance in metres and t is time in seconds.
    • On a distance-time graph, the gradient of the line represents speed; a steeper gradient means a higher speed.
    • To convert km/h to m/s, divide by 3.6; for example, 36 km/h = 10 m/s.
    • A final answer for speed should include the unit m/s and be given to an appropriate number of significant figures.

    Common mistakes and how to put them right

    • Using distance in km and time in hours but giving the answer in m/s without converting.

      Put it right: Convert km to m and hours to seconds before dividing.

    • Confusing speed with velocity.

      Put it right: For speed, give magnitude only.

    • Reading the vertical axis of a distance-time graph as speed.

      Put it right: Speed is the gradient, not the vertical value.

    Exam tips

    • Write down v = s / t, then substitute distance in metres and time in seconds before calculating.
    • Check that the unit of your answer matches the unit asked for; convert km/h to m/s by dividing by 3.6 if needed.
    • On a distance-time graph, calculate speed by choosing two points on the line and dividing the change in distance by the change in time.

    Try the lesson

    The start of the Speed: speed, v, in metres per second, m/s lesson, made from checked teaching notes for this specification point.

    Have a go first

    Which of the following correctly identifies the standard symbol for speed and its standard unit in physics?

    Listen

    Speed, v, is the rate of change of distance with time, measured in metres per second (m/s). It is a scalar quantity, so direction is not specified. You calculate average speed using v = s / t, where s is distance in metres and t is time in seconds. For example, a runner who covers 400 m in 50 s has an average speed of 400 / 50 = 8 m/s. On a distance-time graph, speed is the gradient of the line. You must be able to convert units such as km/h to m/s, substitute correctly into the equation, and interpret the result. Always include the unit m/s and consider whether the value is realistic. A strong answer earns marks for these points. Speed is the distance travelled per unit time and is a scalar quantity, so direction is not required. The SI unit of speed is metres per second, symbol m/s; other units such as km/h must be converted before substitution. Average speed is calculated using v = s / t, where s is distance in metres and t is time in seconds. On a distance-time graph, the gradient of the line represents speed; a steeper gradient means a higher speed. A common slip: Using distance in km and time in hours but giving the answer in m/s without converting. Instead, convert km to m and hours to seconds before dividing. Exam tip: Write down v = s / t, then substitute distance in metres and time in seconds before calculating.

    See it

    A flowchart with three routes leading to speed in metres per second, m/s. In the first route, two boxes, distance travelled s in metres and time taken t in seconds, both point to a box reading average speed v = s / t, which points to the box speed in metres per second, m/s. In the second route, a box reading speed in km/h points to a box reading divide by 3.6, which also points to the box speed in metres per second, m/s. In the third route, a box reading distance-time graph points to a box reading gradient of the line is speed, which also points to the box speed in metres per second, m/s.
    It shows how average speed is calculated from distance and time, how km/h is converted to m/s, and how speed is found from the gradient of a distance-time graph.

    Key words

    Say what each word means before you turn the card.

    Speed

    Try answering aloud or in your head before turning the card.

    Scalar quantities

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    Graph interpretation

    Try answering aloud or in your head before turning the card.

    Measurement and units

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    See every definition
    Speed
    The distance travelled per unit time, a scalar quantity so direction is not required, measured in metres per second (m/s).
    Scalar quantities
    Quantities for which direction is not specified, as with speed, which gives magnitude only.
    Graph interpretation
    Reading a distance-time graph so that the gradient of the line represents speed, with a steeper gradient meaning a higher speed.
    Measurement and units
    Giving a final answer for speed with the unit m/s, converting other units such as km/h before substitution.

    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 with three routes leading to speed in metres per second, m/s. In the first route, two boxes, distance travelled s in metres and time taken t in seconds, both point to a box reading average speed v = s / t, which points to the box speed in metres per second, m/s. In the second route, a box reading speed in km/h points to a box reading divide by 3.6, which also points to the box speed in metres per second, m/s. In the third route, a box reading distance-time graph points to a box reading gradient of the line is speed, which also points to the box speed in metres per second, m/s.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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