Speed & Distance-Time Graphs
Calculate average speed using the equation speed = distance ÷ time, represent journeys on distance-time graphs, and interpret gradient as speed and flat sections as stationary periods
What a learner can do afterwards
- Uses speed = distance ÷ time to calculate average speed with correct units (m/s, km/h)
- Draws a distance-time graph for a given journey with correct axes and labels
- Reads a distance-time graph to determine speed, stopping points, and direction of travel
- Identifies which section of a distance-time graph represents the fastest speed
The lesson
Speed tells you how fast something is moving. You work it out with a simple rule: speed = distance ÷ time. If a cyclist travels 20 kilometres in 4 hours, their average speed is 20 ÷ 4 = 5 kilometres per hour (km/h).
You already know how to read a distance-time graph. Now look closer at the slope, or gradient, of the line. A steep line means the distance is changing fast, so the speed is high. A gentle line means a slower speed. A flat, level line means the distance is not changing at all, so the object is stationary.
Mia's distance-time graph shows her walking 6 km in the first 2 hours, then a flat line for 1 hour while she eats lunch, then 4 km more in the next 2 hours. Her fastest section is the first 2 hours, because the line is steepest there. Her overall average speed uses the whole trip: total distance ÷ total time = 10 km ÷ 5 hours = 2 km/h.
Flat does not mean slow, it means stopped. Compare the steepness of different sections to find out which part of a journey was fastest.
Gradient shows speed: steeper means faster, flat means stopped, and average speed always comes from total distance ÷ total time.
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