Speed, Distance and Time

Calculate speed, distance and time and interpret motion graphs.

~18 min Science

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Speed tells us how fast something moves.

In this lesson you will:

Use the speed formula correctly.
Convert between common units.
Read a simple distance-time graph.

The Formula

Average speed is distance divided by time: speed = distance ÷ time. Rearranged, distance = speed × time and time = distance ÷ speed.

Units

Speed is usually measured in metres per second (m/s) or kilometres per hour (km/h). To change km/h to m/s, divide by 3.6. To change m/s to km/h, multiply by 3.6.

Reading a Graph

On a distance-time graph, a steeper line means greater speed. A flat line means the object is stationary. A curve means the speed is changing.

Worked example

A cyclist travels 600 m in 40 s. Speed = 600 ÷ 40 = 15 m/s.

A car travels at 72 km/h for 2 hours. Distance = 72 × 2 = 144 km.

A runner covers 100 m at 5 m/s. Time = 100 ÷ 5 = 20 s.

Warning Always include units in your answer. A number without a unit is incomplete.

Practice

A bus covers 180 km in 3 hours. Find its average speed.
Convert 90 km/h to m/s.
How long does a train take to cover 240 km at 80 km/h?

Recap

Speed = distance ÷ time. Units matter, and a distance-time graph makes motion easy to compare.

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Course contents

Force, Motion and Energy

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