Distance-time graphs

    OCR
    GCSE

    Distance-time graphs graphically represent the change in an object's position relative to a starting point over time. The gradient of the line is the definitive measure of speed; straight lines indicate constant speed, while horizontal lines denote a stationary object. Curved sections represent non-uniform motion (acceleration or deceleration), requiring the construction of tangents to determine instantaneous speed. Candidates must interpret these visual datasets to describe motion qualitatively and calculate specific kinematic values.

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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 a horizontal line indicates the object is stationary (speed is 0 m/s)
    • Award 1 mark for calculating speed by determining the gradient (change in distance divided by change in time) of a linear section
    • Credit responses that identify a steeper gradient corresponds to a higher speed
    • Award 1 mark for drawing a tangent to a curved line at a specific time point (Higher Tier only)
    • Award 1 mark for calculating the gradient of the drawn tangent to determine instantaneous speed (Higher Tier only)

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly identified the stationary section. Now, ensure you show your working for the gradient calculation clearly on the graph itself"
    • "Be careful with the axes—you interpreted this as a velocity-time graph. Remember: on a distance-time graph, a flat line means zero movement"
    • "Good attempt at the calculation, but your tangent was drawn too thickly/inaccurately. Use a sharp pencil and a ruler to touch the curve at exactly one point"
    • "You have calculated the average speed correctly. To access higher marks, use a tangent to find the speed at the specific instant requested"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating that a horizontal line indicates the object is stationary (speed is 0 m/s)
    • Award 1 mark for calculating speed by determining the gradient (change in distance divided by change in time) of a linear section
    • Credit responses that identify a steeper gradient corresponds to a higher speed
    • Award 1 mark for drawing a tangent to a curved line at a specific time point (Higher Tier only)
    • Award 1 mark for calculating the gradient of the drawn tangent to determine instantaneous speed (Higher Tier only)

    Examiner Tips

    Expert advice for maximising your marks

    • 💡Always check the y-axis label first; if it says 'Distance', a horizontal line means stopped. If it says 'Velocity', it means constant speed
    • 💡When calculating a gradient, select two points on the line that are as far apart as possible to minimize reading errors and maximize accuracy
    • 💡For Higher Tier questions involving curves, you must physically draw the tangent on the graph paper; examiners often award a specific mark just for the construction of the tangent line
    • 💡Use a sharp pencil and a clear ruler for all graph constructions; thick lines can lead to tolerance penalties in gradient calculations

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Confusing distance-time graphs with velocity-time graphs, incorrectly interpreting a horizontal line as 'constant speed' rather than 'stationary'
    • Calculating the gradient as 'change in x over change in y' (run over rise) instead of 'rise over run'
    • Attempting to calculate instantaneous speed on a curve by dividing the coordinates (y/x) at that point, rather than drawing a tangent
    • Failing to convert units (e.g., minutes to seconds) before calculating the gradient, leading to order-of-magnitude errors

    Study Guide Available

    Comprehensive revision notes & examples

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    Key Terminology

    Essential terms to know

    Calculation of speed via gradient
    Interpretation of stationary and constant motion
    Non-uniform motion and tangents
    Graphical translation of kinematic data

    Likely Command Words

    How questions on this topic are typically asked

    Describe
    Calculate
    Determine
    Compare
    Explain

    Practical Links

    Related required practicals

    • •{"code":"P1.2","title":"Investigation of motion","relevance":"Data collected from trolleys on ramps or walking experiments is often plotted as distance-time graphs for analysis"}

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