Changing motion

    OCR
    GCSE

    Changing motion encompasses the quantitative analysis of acceleration as the rate of change of velocity, governed by Newton's Second Law ($F=ma$). Candidates must demonstrate proficiency in interpreting velocity-time graphs, specifically deriving acceleration from gradients and displacement from the area under the curve. The relationship between resultant force, mass, and acceleration defines the concept of inertial mass, quantifying the resistance of an object to changes in velocity. Mastery requires applying the uniform acceleration equations, including $v^2 - u^2 = 2as$, to solve complex kinematic problems.

    0
    Objectives
    3
    Exam Tips
    4
    Pitfalls
    4
    Key Terms
    5
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for correct substitution of values into the acceleration equation a = (v-u)/t before rearrangement
    • Award 1 mark for calculating the gradient of a velocity-time graph to determine acceleration, including correct units (m/s²)
    • Credit responses that identify the area under a velocity-time graph as representing the distance travelled or displacement
    • Award 1 mark for stating that a resultant force is required to produce a change in motion (acceleration), linking to Newton's Second Law
    • For Higher Tier, award marks for drawing a tangent to a curve on a velocity-time graph to estimate acceleration at a specific time

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly calculated the value, but lost a mark for missing the unit (m/s²) — always double-check units in motion questions"
    • "Your tangent is drawn correctly, but your gradient calculation uses points that are too close together; use a larger triangle for better accuracy"
    • "You stated the object stopped, but the graph shows constant velocity. Remember: zero gradient on a v-t graph means constant speed, not zero speed"
    • "Excellent application of F=ma. To improve, explicitly state how the increase in mass affects acceleration if the force remains constant"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for correct substitution of values into the acceleration equation a = (v-u)/t before rearrangement
    • Award 1 mark for calculating the gradient of a velocity-time graph to determine acceleration, including correct units (m/s²)
    • Credit responses that identify the area under a velocity-time graph as representing the distance travelled or displacement
    • Award 1 mark for stating that a resultant force is required to produce a change in motion (acceleration), linking to Newton's Second Law
    • For Higher Tier, award marks for drawing a tangent to a curve on a velocity-time graph to estimate acceleration at a specific time

    Examiner Tips

    Expert advice for maximising your marks

    • 💡Always check the axes of motion graphs immediately; the interpretation of the gradient changes entirely between distance-time and velocity-time graphs
    • 💡When asked to estimate acceleration from a curved graph, you must draw a tangent at the specified time and calculate its gradient—do not just use the coordinates of the point
    • 💡Memorise that inertial mass is defined specifically as the ratio of force over acceleration (m = F/a); this is a frequent 1-mark definition question on Higher Tier papers

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Confusing negative acceleration (deceleration) with moving backwards; candidates often fail to recognise it means slowing down when velocity is positive
    • Misinterpreting a horizontal line on a velocity-time graph as 'stationary' (which is true for distance-time graphs) rather than 'constant velocity'
    • Failing to convert units before calculation, specifically leaving mass in grams or time in minutes when using F=ma or acceleration formulae
    • Calculating the mean speed instead of acceleration when given initial and final velocities

    Key Terminology

    Essential terms to know

    Newton's Second Law ($F=ma$)
    Velocity-time graph analysis (gradients and areas)
    Uniform acceleration equations
    Inertial mass and resistance to motion

    Likely Command Words

    How questions on this topic are typically asked

    Calculate
    Describe
    Explain
    Estimate
    Plot

    Practical Links

    Related required practicals

    • •{"code":"PAG P2","title":"Investigation of Force, Mass and Acceleration","relevance":"Experimental verification of Newton's Second Law using trolleys and light gates/ticker timers"}

    Ready to test yourself?

    Practice questions tailored to this topic