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Distance-time graphs

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Lesson notes

What is a distance-time graph?

  • A **distance-time graph** shows how far an object has travelled over time.
  • Time is plotted on the **x-axis** (horizontal) and distance on the **y-axis** (vertical).
  • The **gradient** (steepness) of the line represents the **speed** of the object.
  • A steeper gradient means a **greater speed**.

Calculating speed from the gradient

  • Gradient = change in distance ÷ change in time = Δy / Δx.
  • This is the same as the speed equation: **speed = distance ÷ time**.
  • Example: A jogger travels 25 m in 5 s → speed = 25 ÷ 5 = **5 m/s**.
  • Another jogger travels 25 m in 10 s → speed = 25 ÷ 10 = **2.5 m/s**.

Interpreting different shapes

  • A **straight, sloping line** indicates **constant speed**.
  • A **horizontal line** means the object is **stationary** (not moving).
  • A **curved line** shows **changing speed** (acceleration or deceleration).
  • If the gradient **decreases** over time, the object is **decelerating** (slowing down).
  • If the gradient **increases** over time, the object is **accelerating** (speeding up).

Comparing speeds on the same graph

  • When two lines are plotted, the **steeper line** corresponds to the **faster object**.
  • You can compare speeds by calculating the gradient of each line.
  • The line with the larger gradient has the higher speed.

Distance-time graph comparing two joggers. The steeper blue line shows a higher speed (5 m/s) than the red line (2.5 m/s).

Distance-time graph for two joggersTime (s)Distance (m)Faster (5 m/s)Slower (2.5 m/s)

Curved distance-time graphs: the blue curve (decreasing gradient) shows deceleration; the red curve (increasing gradient) shows acceleration.

Acceleration and decelerationTime (s)Distance (m)DeceleratingAccelerating

Slides

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Practice questions

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  1. 1.What does the gradient of a distance-time graph represent?

    Easy
    • ASpeed
    • BAcceleration
    • CDistance
    • DTime
  2. 2.What is the equation for speed?

    Easy
    • ASpeed = Distance × Time
    • BSpeed = Distance ÷ Time
    • CSpeed = Time ÷ Distance
    • DSpeed = Distance + Time
  3. 3.A jogger runs 25 m in 5 s. What is their speed?

    Medium
    • A5 m/s
    • B0.2 m/s
    • C125 m/s
    • D30 m/s
  4. 4.A jogger runs 25 m in 10 s. What is their speed?

    Medium
    • A2.5 m/s
    • B0.4 m/s
    • C250 m/s
    • D15 m/s
  5. 5.In a distance-time graph, a steeper gradient indicates:

    Medium
    • AGreater speed
    • BLower speed
    • CConstant speed
    • DZero speed
  6. 6.On a distance-time graph, a horizontal line indicates:

    Medium
    • AThe object is stationary
    • BThe object is moving at constant speed
    • CThe object is accelerating
    • DThe object is decelerating
  7. 7.What does a decreasing gradient on a distance-time graph represent?

    Medium
    • ADeceleration
    • BAcceleration
    • CConstant speed
    • DStationary object
  8. 8.What does an increasing gradient on a distance-time graph represent?

    Medium
    • AAcceleration
    • BDeceleration
    • CConstant speed
    • DStationary object

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