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Distance vs displacement
Beginner
Distance is path length; displacement is net change in position.
Distance is the total path length and is never negative. Displacement is the straight-line change in position from start to end, with direction, and can be zero or negative.
Running one lap of a 400 m track: distance 400 m, displacement 0.
Average speed uses distance; average velocity uses displacement. Don't swap them.
In more detail
Distance is the total length of the path travelled, while displacement is the straight-line change in position from start to end. Displacement is a vector and can be zero even when distance is not.
Real-world uses
- A runner on a 400 m track has travelled 400 m of distance but zero displacement after one lap.
- Taxi fares usually depend on distance, while a delivery company may care about displacement.
- A runner who goes round a 400 m track and returns to the start covers 400 m of distance but has zero displacement.
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Frequently asked questions
Can displacement be larger than distance?
No. The magnitude of displacement is always less than or equal to the distance travelled.
Is displacement a scalar?
No. It is a vector, because it has both magnitude and direction.
Can distance be negative?
No. Distance is always zero or positive. Displacement can be negative when the motion is in the negative direction.
Related topics in Kinematics
Rest and motion · Reference frames · Speed vs velocity · Average velocity · Instantaneous velocity