AQA · GCSE · Combined Science

    Course version: 8464 · Version from Sept 2018

    Momentum, p, in kilograms metre per second, kg m/s

    Full specification wording

    Momentum is a property of moving objects: momentum, p, in kilograms metre per second, kg m/s

    Momentum is a property of moving objects, assessed at Higher Tier only.

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

    • Point 4 of 6
    • 3 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Momentum is a property of moving objects, assessed at Higher Tier only. It is calculated using the equation p = m × v, where p is momentum, m is mass in kilograms, and v is velocity in metres per second. Because mass is measured in kg and velocity in m/s, the unit of momentum is the kilogram metre per second, kg m/s. For example, a 2 kg trolley moving at 3 m/s has a momentum of p = 2 × 3 = 6 kg m/s. Momentum is a vector quantity, meaning both its magnitude and direction are important. Consequently, an object moving in the opposite direction will have a negative momentum if the initial direction is defined as positive. Understanding this vector nature is crucial when analysing the motion of objects.

    What earns the marks

    • States that momentum is calculated using p = m × v, with p as momentum, m as mass and v as velocity.
    • Uses the correct unit, kg m/s, and recognises that it comes from multiplying kg by m/s.
    • Substitutes mass in kilograms and velocity in metres per second into the equation without mixing units.
    • Recognises that momentum is a vector quantity, so direction must be considered when assigning positive or negative values.
    • Rearranges p = m × v correctly to find mass or velocity when momentum is known.

    Common mistakes and how to put them right

    • Using grams instead of kilograms for mass.

      Put it right: Divide grams by 1000 before calculating momentum.

    • Writing the unit as kg/m/s or kg m s.

      Put it right: Write kg m/s, which is kilogram metre per second.

    • Treating momentum as a scalar and ignoring direction.

      Put it right: Assign positive and negative signs to opposite directions.

    Exam tips

    • Always write the equation p = m × v before substituting values, then show the substitution with units.
    • When a question involves opposite directions, state which direction is positive and give momentum values with signs.

    Try the lesson

    The start of the Momentum is a property of moving objects: momentum, p, in kilograms metre per second, kg m/s lesson, made from checked teaching notes for this specification point.

    Have a go first

    A student calculates the momentum of a moving bicycle. Which of the following is the correct standard unit they should use for their answer?

    Listen

    Momentum is a property of moving objects, assessed at Higher Tier only. It is calculated using the equation p = m × v, where p is momentum, m is mass in kilograms, and v is velocity in metres per second. Because mass is measured in kg and velocity in m/s, the unit of momentum is the kilogram metre per second, kg m/s. For example, a 2 kg trolley moving at 3 m/s has a momentum of p = 2 × 3 = 6 kg m/s. Momentum is a vector quantity, meaning both its magnitude and direction are important. Consequently, an object moving in the opposite direction will have a negative momentum if the initial direction is defined as positive. Understanding this vector nature is crucial when analysing the motion of objects. A strong answer earns marks for these points. States that momentum is calculated using p = m × v, with p as momentum, m as mass and v as velocity. Uses the correct unit, kg m/s, and recognises that it comes from multiplying kg by m/s. Substitutes mass in kilograms and velocity in metres per second into the equation without mixing units. Recognises that momentum is a vector quantity, so direction must be considered when assigning positive or negative values. A common slip: Using grams instead of kilograms for mass. Instead, divide grams by 1000 before calculating momentum. Exam tip: Always write the equation p = m × v before substituting values, then show the substitution with units.

    See it

    A flowchart running from top to bottom. Two boxes at the top, one labelled 'Mass, m, in kilograms' and one labelled 'Velocity, v, in metres per second', both have arrows pointing down into a box labelled 'p = m × v'. An arrow points from that box down to a box labelled 'Momentum, p, in kg m/s'. An arrow points from that box down to a box labelled 'Vector quantity: direction matters', and an arrow points from that box down to a final box labelled 'Opposite direction gives negative momentum'.
    It shows how mass in kilograms and velocity in metres per second combine in p = m × v to give momentum in kg m/s, and that momentum is a vector so opposite directions give negative values.

    Key words

    Say what each word means before you turn the card.

    Momentum

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

    Kilogram metre per second

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

    Vector quantity

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

    See every definition
    Momentum
    A property of moving objects, given the symbol p, calculated using the equation p = m × v.
    Kilogram metre per second
    The unit of momentum, kg m/s, which comes from multiplying kilograms by metres per second.
    Vector quantity
    A quantity for which both magnitude and direction are important, so an object moving in the opposite direction has negative momentum if the initial direction is positive.

    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 at the top, one labelled 'Mass, m, in kilograms' and one labelled 'Velocity, v, in metres per second', both have arrows pointing down into a box labelled 'p = m × v'. An arrow points from that box down to a box labelled 'Momentum, p, in kg m/s'. An arrow points from that box down to a box labelled 'Vector quantity: direction matters', and an arrow points from that box down to a final box labelled 'Opposite direction gives negative momentum'.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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