AQA · GCSE · Physics

    Course version: 8463 · Version from Sept 2016

    Speed: Speed does not involve direction. Speed is a scalar quantity.

    Speed says how quickly distance is covered and nothing about which way.

    Checked against the AQA 8463 specification (opens in a new tab) on .

    • Point 1 of 9
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Speed says how quickly distance is covered and nothing about which way. Because it is a scalar, a car going round a bend at a steady 13 m/s has a constant speed even though it is changing direction all the time. Average speed is the total distance divided by the total time, which is what average-speed cameras compute from the separation of the cameras and the time between them; instantaneous speed is the speed at one moment, and that is what a speedometer shows. The two differ whenever the motion is not steady, so stopping at traffic lights lowers the average without changing the reading during steady driving. A speed can never be negative, because neither a distance nor a time can be.

    What earns the marks

    • Speed as a measure of the distance travelled in a given time, with no direction.
    • A scalar having magnitude only.
    • Average speed calculated as total distance divided by total time.
    • Distinguishing average speed from instantaneous speed.

    Common mistakes and how to put them right

    • Writing that a car going round a corner at a steady rate has a changing speed.

    • Giving a speed with a direction attached and still calling it a speed.

    • Using only part of the journey's distance when calculating an average speed.

    • Treating a speedometer reading as the average speed for the journey.

    Exam tips

    • If the question says average, use totals for both the distance and the time.
    • Watch for the word direction in a question; it is usually asking about velocity rather than speed.

    Try the lesson

    The start of the Speed: Speed does not involve direction. Speed is a scalar quantity. lesson, made from checked teaching notes for this specification point.

    Have a go first

    Which quantity is a scalar quantity because it does not involve direction?

    Listen

    Speed says how quickly distance is covered and nothing about which way. Because it is a scalar, a car going round a bend at a steady 13 m/s has a constant speed even though it is changing direction all the time. Average speed is the total distance divided by the total time, which is what average-speed cameras compute from the separation of the cameras and the time between them; instantaneous speed is the speed at one moment, and that is what a speedometer shows. The two differ whenever the motion is not steady, so stopping at traffic lights lowers the average without changing the reading during steady driving. A speed can never be negative, because neither a distance nor a time can be. A strong answer earns marks for these points. speed as a measure of the distance travelled in a given time, with no direction. a scalar having magnitude only. average speed calculated as total distance divided by total time. distinguishing average speed from instantaneous speed. Exam tip: If the question says average, use totals for both the distance and the time.

    See it

    A flowchart starting from a top node labelled Speed: distance covered in a given time, no direction. Four branches lead from it. One goes to Scalar quantity: magnitude only. One goes to Average speed = total distance ÷ total time, which in turn leads to Average-speed cameras: separation of cameras and time between them, and to Stopping at traffic lights lowers the average. One goes to Instantaneous speed: speed at one moment, which leads to Speedometer shows instantaneous speed and to Reading during steady driving unchanged. The last branch goes to Speed can never be negative.
    It shows speed as a scalar with no direction, and how average speed and instantaneous speed differ.

    Key words

    Say what each word means before you turn the card.

    speed as a scalar

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

    average speed

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

    instantaneous speed

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

    total distance over total time

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

    See every definition
    speed as a scalar
    A quantity that says how quickly distance is covered and nothing about which way, having magnitude only.
    average speed
    The total distance divided by the total time, which is what average-speed cameras compute from the separation of the cameras and the time between them.
    instantaneous speed
    The speed at one moment, and that is what a speedometer shows.
    total distance over total time
    The calculation of average speed, using totals for both the distance and the time.

    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 starting from a top node labelled Speed: distance covered in a given time, no direction. Four branches lead from it. One goes to Scalar quantity: magnitude only. One goes to Average speed = total distance ÷ total time, which in turn leads to Average-speed cameras: separation of cameras and time between them, and to Stopping at traffic lights lowers the average. One goes to Instantaneous speed: speed at one moment, which leads to Speedometer shows instantaneous speed and to Reading during steady driving unchanged. The last branch goes to Speed can never be negative.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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