Newton's First Law

    OCR
    GCSE

    Newton's First Law establishes the fundamental relationship between force and motion, stating that an object remains at rest or in uniform motion in a straight line unless acted upon by a resultant force. This principle defines inertia as the inherent resistance of an object to changes in velocity, a property directly proportional to its mass. Mastery requires the ability to analyze free-body diagrams to determine if a system is in equilibrium and to predict the subsequent motion based on the presence or absence of a net force, distinguishing clearly between the mechanics of starting motion and sustaining motion.

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    Objectives
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    Exam Tips
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    Pitfalls
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    Key Terms
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    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for stating that an object remains at rest or moves at a constant velocity unless acted upon by a resultant force
    • Credit responses that explicitly link zero resultant force to zero acceleration
    • Award 1 mark for identifying that a change in direction (even at constant speed) requires a non-zero resultant force
    • Credit the definition of inertia as the tendency of an object to continue in its state of rest or uniform motion

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly identified the forces, but you must specify 'resultant force' to earn the mark"
    • "Good definition, but you missed the 'constant velocity' aspect—remember moving objects don't stop without a force"
    • "You stated the object slows down, but didn't explain *why* in terms of resistive forces exceeding driving forces"
    • "Excellent application of the law; to improve, explicitly mention that a change in direction constitutes a change in velocity"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating that an object remains at rest or moves at a constant velocity unless acted upon by a resultant force
    • Credit responses that explicitly link zero resultant force to zero acceleration
    • Award 1 mark for identifying that a change in direction (even at constant speed) requires a non-zero resultant force
    • Credit the definition of inertia as the tendency of an object to continue in its state of rest or uniform motion

    Examiner Tips

    Expert advice for maximising your marks

    • 💡Use the term 'resultant force' or 'net force' in every explanation; 'balanced forces' is acceptable but less precise for higher marks
    • 💡When explaining terminal velocity, explicitly state 'forces are balanced therefore resultant force is zero, so acceleration is zero'
    • 💡Remember that 'constant velocity' implies both constant speed and constant direction; if direction changes, Newton's First Law implies a force is acting

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Asserting that a constant driving force is needed to maintain constant velocity (Aristotelian misconception)
    • Stating that an object with zero resultant force must be stationary, ignoring the possibility of constant velocity
    • Confusing 'constant speed' with 'constant velocity' when analyzing objects in circular motion
    • Failing to use the specific term 'resultant force', referring vaguely to 'forces' being equal without mentioning the net effect

    Key Terminology

    Essential terms to know

    Inertia and the definition of inertial mass
    Equilibrium and zero resultant force
    Uniform velocity versus acceleration
    Free-body diagrams and vector resolution

    Likely Command Words

    How questions on this topic are typically asked

    State
    Explain
    Describe
    Predict
    Suggest

    Practical Links

    Related required practicals

    • •{"code":"PAG 2","title":"Investigation of Acceleration","relevance":"Newton's First Law establishes the control condition (friction compensation) for N2 experiments"}

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