Newton's Second Law

    OCR
    GCSE

    Newton's Second Law defines the fundamental relationship between the resultant force acting on an object, its mass, and the acceleration produced. It establishes that acceleration is directly proportional to the resultant force and inversely proportional to the mass, mathematically expressed as F = ma. This topic encompasses the concept of inertial mass as a measure of resistance to change in velocity and requires the application of vector analysis to determine resultant forces in dynamic systems. Mastery involves both theoretical calculation and the experimental verification of these proportionality relationships.

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    Objectives
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    Exam Tips
    4
    Pitfalls
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    Key Terms
    5
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for correct rearrangement of the formula to subject acceleration: a = F/m
    • Credit substitution of correct values with compatible units, specifically converting grams to kilograms where necessary
    • Award 1 mark for stating that acceleration is directly proportional to the resultant force for a fixed mass
    • For inertial mass definitions, candidates must explicitly state it is the ratio of force over acceleration (m = F/a)
    • In practical contexts, credit reference to 'compensating for friction' by tilting the runway

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly identified the formula, but check your units—mass must be in kg for the result to be in Newtons"
    • "Your definition of inertial mass is vague; explicitly define it as the ratio of force to acceleration"
    • "You stated the trend correctly, but to gain the mark for 'Explain', you must reference the linear relationship shown in the data"
    • "Be careful with system mass; remember the force accelerates both the trolley AND the hanging mass"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for correct rearrangement of the formula to subject acceleration: a = F/m
    • Credit substitution of correct values with compatible units, specifically converting grams to kilograms where necessary
    • Award 1 mark for stating that acceleration is directly proportional to the resultant force for a fixed mass
    • For inertial mass definitions, candidates must explicitly state it is the ratio of force over acceleration (m = F/a)
    • In practical contexts, credit reference to 'compensating for friction' by tilting the runway

    Examiner Tips

    Expert advice for maximising your marks

    • 💡In calculation questions, always write down the rearranged equation before substituting values to secure method marks even if the final calculation is incorrect
    • 💡When describing relationships from graphs, use the specific phrase 'directly proportional' (straight line through origin) rather than just 'as X increases, Y increases'
    • 💡For PAG P3 questions, remember that adding mass to the trolley changes the total mass, but adding mass to the hanger changes the force; distinguish these effects clearly

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Failing to convert mass from grams (g) to kilograms (kg) before substitution into F=ma, leading to answers off by a factor of 1000
    • Confusing the 'accelerating force' (weight of hanging mass) with the 'total mass being accelerated' (trolley + hanging mass) in system calculations
    • Stating that a constant resultant force results in a constant velocity rather than a constant acceleration
    • Rearranging the equation incorrectly as a = m/F

    Study Guide Available

    Comprehensive revision notes & examples

    Read Study Guide

    Key Terminology

    Essential terms to know

    Proportionality of acceleration to resultant force and inverse proportionality to mass
    Definition and calculation of inertial mass
    Vector nature of force and acceleration
    Experimental verification using dynamic trolleys and light gates
    Calculation of resultant forces in one dimension

    Likely Command Words

    How questions on this topic are typically asked

    Calculate
    Explain
    Describe
    Determine
    Suggest
    Define

    Practical Links

    Related required practicals

    • •{"code":"PAG P3","title":"Investigation of Force, Mass and Acceleration","relevance":"Experimental verification of Newton's Second Law using trolleys and light gates/ticker timers"}

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