Distance-time graphs

Time goes along the bottom, distance goes up the side.

Every point is "at this time, it had gone this far".

• O to A: steep line, moving fast.
• A to B: flat line, distance not changing, so stationary.
• B to C: shallower line, moving more slowly.

The gradient of a distance-time graph is the speed.

Pick two points on a straight section:

1. gradient = change in distance ÷ change in time
2. O to A: 40 m ÷ 20 s = 2 m/s
3. B to C: (60 − 40) m ÷ (60 − 35) s = 20 ÷ 25 = 0.8 m/s

A curved line means the speed is changing. Getting steeper: speeding up. Getting flatter: slowing down. For the speed at one moment on a curve, draw a tangent (a straight line that just touches the curve) and find its gradient. That is in the Plus questions for this lesson.