Distance and displacement
An athlete runs to the end of a track and turns back. How far did the athlete run? How far is the athlete from the start?
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Step 1 of 4
- An athlete starts at O.
- The athlete runs 80 m out to A.
- The athlete turns and runs 40 m back to B.
- Distance 120 m. Displacement OB 40 m.
The athlete ran 80 m + 40 m = 120 m. The athlete is 80 − 40 = 40 m from the start, at B.
The rule
Distance is the whole length of the path. Displacement is the change in position, with a direction.
Both are measured in metres. Distance has no direction. Displacement does: from the first position towards the last.
Take a straight line. Distance and displacement match only if the object never turns back.
A curve is different. On a quarter circle the path is longer than the displacement. The path bends. Displacement looks only at the start and the end.
| Distance | Displacement | |
|---|---|---|
| Means | Length of the whole path | Change in position |
| Direction | None | Yes |
| Ball thrown up, caught at the start | Up and down: 2 × height | 0 |
| Fuel used depends on it | Yes | No |