Speed, velocity and distance-time graphs

The idea

Distance is how far an object moves (scalar); displacement includes direction (vector). Speed = distance ÷ time; velocity is speed in a given direction. Typical speeds: walking about 1.5 m/s, running about 3 m/s, cycling about 6 m/s, sound in air about 330 m/s. On a distance–time graph the gradient is the speed; a flat line means the object is stationary.

1. Use s = vt with metres and seconds.
2. On a distance–time graph, find the gradient for speed.
3. Remember direction for velocity.

Watch out An object moving in a circle at constant speed has a changing velocity, because its direction changes.