Distance and Displacement

Distance is the total path length; displacement is the straight-line change in position from start to end. Distance is a scalar, displacement is a vector.

Distance

Distance is the total length of the path actually travelled by an object. It is a scalar quantity—it has magnitude only, no direction. The SI unit is the metre (m). For example, if you walk 3 m east and then 4 m north, the distance travelled is 7 m.

Displacement

Displacement is the change in position of an object from its initial position to its final position. It is a vector: it has both magnitude and direction. Displacement is the straight line from start to end, regardless of the path taken. In the example above, the displacement is 5 m in a direction between east and north (by Pythagoras).

Distance vs displacement

Distance is always positive or zero; displacement can be positive, negative, or zero (when the object returns to the start). For motion in one dimension along a line, we often take displacement as positive in one direction and negative in the other. The magnitude of displacement is less than or equal to the distance.

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