AQA · GCSE · Combined Science

    Course version: 8464 · Version from Sept 2018

    Newton's Second Law: mass, m, in kilograms, kg

    Mass measures the quantity of matter in an object and is measured in kilograms (kg).

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

    • Point 7 of 13
    • 3 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Mass measures the quantity of matter in an object and is measured in kilograms (kg). In Newton's second law, F = m × a, mass is the constant that links force in newtons to acceleration in m/s². A larger mass accelerates less for the same resultant force. For example, a 2 kg trolley pushed with a resultant force of 6 N accelerates at 3 m/s² because 6 N ÷ 2 kg = 3 m/s². If the mass were 3 kg, the same 6 N would give only 2 m/s². Always convert grams to kilograms by dividing by 1000 before substituting into F = m × a, and remember that mass is not the same as weight; weight is a force measured in newtons and depends on gravitational field strength.

    What earns the marks

    • State that mass is measured in kilograms (kg) and is a scalar quantity representing the amount of matter.
    • Use the correct unit kg in calculations and final answers, converting grams to kilograms where necessary.
    • Rearrange F = m × a correctly to m = F ÷ a when mass is the unknown.
    • Substitute numerical values with consistent units before calculating, for example 500 g = 0.5 kg.
    • Interpret a larger mass as producing a smaller acceleration for the same resultant force.
    • Distinguish mass (kg) from weight (N) and explain that weight = mass × gravitational field strength.

    Common mistakes and how to put them right

    • Using grams directly in F = m × a without converting to kilograms.

      Put it right by dividing grams by 1000 first.

    • Confusing mass with weight and giving newtons as the unit of mass.

      Put it right by stating mass is in kg and weight is a force in N.

    • Rearranging F = m × a incorrectly, for example writing m = a ÷ F.

      Put it right by dividing force by acceleration, m = F ÷ a.

    Exam tips

    • Write the equation, substitute values with units, then calculate and give the unit kg in your final answer.
    • Check whether a mass is given in grams and convert to kilograms before using it in any calculation.
    • If asked to compare accelerations, refer to the inverse relationship: doubling mass halves acceleration for the same force.

    Try the lesson

    The start of the Newton's Second Law: mass, m, in kilograms, kg lesson, made from checked teaching notes for this specification point.

    Have a go first

    In the equation F = m × a, what is the unit of the quantity m?

    Listen

    Mass measures the quantity of matter in an object and is measured in kilograms (kg). In Newton's second law, F = m × a, mass is the constant that links force in newtons to acceleration in m/s². A larger mass accelerates less for the same resultant force. For example, a 2 kg trolley pushed with a resultant force of 6 N accelerates at 3 m/s² because 6 N ÷ 2 kg = 3 m/s². If the mass were 3 kg, the same 6 N would give only 2 m/s². Always convert grams to kilograms by dividing by 1000 before substituting into F = m × a, and remember that mass is not the same as weight; weight is a force measured in newtons and depends on gravitational field strength. A strong answer earns marks for these points. State that mass is measured in kilograms (kg) and is a scalar quantity representing the amount of matter. Use the correct unit kg in calculations and final answers, converting grams to kilograms where necessary. Rearrange F = m × a correctly to m = F ÷ a when mass is the unknown. Substitute numerical values with consistent units before calculating, for example 500 g = 0.5 kg. A common slip: Using grams directly in F = m × a without converting to kilograms. Instead, dividing grams by 1000 first. Exam tip: Write the equation, substitute values with units, then calculate and give the unit kg in your final answer.

    See it

    A flowchart starting with a node labelled 'Mass, m, in kilograms, kg'. An arrow leads down to 'Convert grams to kilograms by dividing by 1000', then to 'Substitute into F = m × a'. From that node two arrows branch out: one to 'Rearrange to m = F ÷ a when mass is unknown' and one to 'Larger mass gives smaller acceleration for the same resultant force'. A separate arrow from the first mass node leads to 'Mass is not the same as weight', then to 'Weight is a force measured in newtons', then to 'Weight = mass × gravitational field strength'.
    It shows how mass in kilograms is converted and used in F = m × a, rearranged for mass, linked to acceleration, and distinguished from weight.

    Key words

    Say what each word means before you turn the card.

    mass

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

    Newton's second law

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

    weight

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

    See every definition
    mass
    Measured in kilograms (kg) and is a scalar quantity representing the amount of matter.
    Newton's second law
    F = m × a, where mass is the constant that links force in newtons to acceleration in m/s².
    weight
    A force measured in newtons that depends on gravitational field strength, and is not the same as mass.

    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 with a node labelled 'Mass, m, in kilograms, kg'. An arrow leads down to 'Convert grams to kilograms by dividing by 1000', then to 'Substitute into F = m × a'. From that node two arrows branch out: one to 'Rearrange to m = F ÷ a when mass is unknown' and one to 'Larger mass gives smaller acceleration for the same resultant force'. A separate arrow from the first mass node leads to 'Mass is not the same as weight', then to 'Weight is a force measured in newtons', then to 'Weight = mass × gravitational field strength'.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

    There is more to this lesson

    The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.

    Carry on with the full lesson

    A week of Premium from your first lesson · Then the free plan continues · No card, no charge

    Test your understanding of Newton's Second Law: mass, m, in kilograms, kg

    Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.

    Take topic quiz

    A week of Premium from your first lesson · Then the free plan continues · No card, no charge

    Start free

    Cookies on MasteryMind

    Essential cookies keep you signed in.

    Analytics and advertising cookies stay off unless you accept.

    Read our Privacy Policy.