Weight

    OCR
    GCSE

    Weight is defined as the force acting on an object due to gravity, distinct from mass which is a measure of the amount of matter in an object. The magnitude of weight is calculated using the equation W = mg, where g represents the gravitational field strength at a specific location. Unlike mass, which remains constant throughout the universe, weight varies depending on the local gravitational field. This vector quantity acts towards the centre of the gravitational field and is measured in Newtons using a calibrated spring balance or newtonmeter.

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    Objectives
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    Exam Tips
    3
    Pitfalls
    4
    Key Terms
    4
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for stating that weight is the force of gravity acting on an object, measured in Newtons (N)
    • Credit responses that explicitly distinguish mass as a measure of matter (scalar) which remains constant regardless of location
    • Award 1 mark for correct substitution into W = m × g, ensuring mass is converted to kilograms
    • Award 1 mark for identifying that weight acts vertically downwards from the object's centre of mass

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly calculated the value, but you used grams instead of kilograms. Remember: Physics equations require SI units (kg)"
    • "Good definition of weight. To improve, explicitly mention that it acts from the 'centre of mass'"
    • "You stated mass changes on the Moon — recall that mass is the amount of matter (constant), only the weight changes because 'g' is lower"
    • "Excellent rearrangement of the formula. Ensure you include the correct unit (N/kg) when solving for gravitational field strength"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating that weight is the force of gravity acting on an object, measured in Newtons (N)
    • Credit responses that explicitly distinguish mass as a measure of matter (scalar) which remains constant regardless of location
    • Award 1 mark for correct substitution into W = m × g, ensuring mass is converted to kilograms
    • Award 1 mark for identifying that weight acts vertically downwards from the object's centre of mass

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When calculating weight, immediately check if mass is in grams; if so, divide by 1000 to convert to kg before doing anything else
    • 💡If asked to explain why weight changes on another planet, structure your answer: Mass is constant → g varies → therefore W varies
    • 💡Use the specific term 'gravitational field strength' (g) rather than just 'gravity' to secure marks in high-tariff explanation questions

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Interchanging the terms 'mass' and 'weight' in explanations, implying they are the same physical quantity
    • Failing to convert mass from grams (g) to kilograms (kg) before substituting into the W = mg equation
    • Stating that an object's mass decreases on the Moon, rather than correctly identifying that the gravitational field strength is lower

    Study Guide Available

    Comprehensive revision notes & examples

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    Key Terminology

    Essential terms to know

    Distinction between mass (scalar) and weight (vector)
    Gravitational field strength (g) and its variation
    Application of the equation W = mg
    Centre of mass as the point of weight application

    Likely Command Words

    How questions on this topic are typically asked

    Calculate
    Explain
    State
    Describe
    Suggest

    Practical Links

    Related required practicals

    • •{"code":"P2.1","title":"Measurement of Weight","relevance":"Use of a newtonmeter (spring balance) to measure weight and verify the relationship with mass"}

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