Distance, Displacement, Speed and Velocity — AQA GCSE Physics
These quantities describe motion. Some are scalars and some are vectors.
Distance and displacement
- Distance is how far an object moves — a scalar (size only).
- Displacement is the straight-line distance and direction from start to finish — a vector.
A runner completing a full lap travels a large distance but ends with zero displacement (back at the start).
Speed and velocity
- Speed is how fast an object moves (distance per unit time) — a scalar.
- Velocity is speed in a given direction — a vector.
$$\text{speed} = \frac{\text{distance}}{\text{time}}$$
Typical speeds
You should know rough everyday speeds:
- walking ≈ 1.5 m/s, running ≈ 3 m/s, cycling ≈ 6 m/s.
- The speed of sound in air is about 330 m/s.
Constant and changing speed
Many objects do not travel at constant speed. The speed can change due to wind, terrain or the activity. Velocity changes if either the speed or the direction changes — so an object moving in a circle at constant speed has a changing velocity (because direction changes).
Exam tips
- Distance/speed are scalars; displacement/velocity are vectors.
- Learn speed = distance ÷ time.
- Know typical speeds (walking, running, cycling, sound).
- Velocity changes if speed or direction changes — important for circular motion.