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
1 · Read
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.
More to read
2.3 Time, Velocity, and Speed
Speed tells you how fast something moves. You find it by dividing distance by time. If a car travels 100 km in 2 hours its average speed is 50 km/h. A distance-time graph shows the journey as a line. The steeper the line the faster the speed. A flat line means the object stopped. You can read the graph to find speed at any section or see when the object changed direction.
3 Ways to Calculate Distance
When you know speed and time you can find distance. The formula is distance = speed x time. If you cycle at 15 km/h for 3 hours you cover 45 km. Distance-time graphs make this visual. The area under a speed-time graph gives distance too. For a journey with different speeds you add up each section distance. Always check your units match.
Solving equations & inequalities: FAQ
Linear equations help model real trips. If you know average speed and time you can calculate distance. The equation distance = speed x time works for constant speed. For changing speeds you break the trip into parts. Graphs show the relationship between distance and time. A straight line means steady speed. A curve means acceleration or deceleration.
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2 · Watch
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Where it sits
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Where this leads
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