Displacement, Distance & Units
The difference between how far you've travelled and where you actually ended up — and the SI units that make the answer precise.
A scalar quantity has only a magnitude (a size) — mass, time, and distance are scalars. A vector quantity has both magnitude and direction — displacement, velocity, and acceleration are vectors.
This distinction matters constantly in kinematics: "5 m" is a distance, but "5 m east" is a displacement. Mixing the two up is one of the most common early mistakes in this topic.
Distance is the total length of the path travelled, regardless of direction. Displacement is the straight-line change in position from start to finish, including direction.
Walk 3 laps of a 400 m track and you've covered a distance of 1200 m — but your displacement is 0 m, because you end up exactly where you started.
Distance and displacement are both measured in metres (m). CAIE expects working in base SI units before applying prefixes — convert cm and km to m first, then apply prefixes to the final answer if the question asks for it.
Common prefixes worth having memorised: kilo- (10³), centi- (10â»Â²), milli- (10â»Â³), micro- (10â»â¶).
On a displacement–time graph, the gradient at any point gives the velocity at that instant. A flat section means the object is stationary; a straight sloped line means constant velocity; a curve means the velocity is changing.
Practice & Solutions
Q1 · Scalar or vector? Open → Q2 · Distance vs. displacement Open → Q3 · Unit conversions Open →3 original questions, with worked solutions.