In Newtonian mechanics, displacement is one of two subtly different quantities measuring distance.

1. (a) Displacement is a vector quantity which expresses the length and direction of a straight line from one place to another (as opposed to the scalar quantity distance which expresses only the length). The SI unit for either distance or displacement is the metre.

2. (b) Displacement implies movement and is a vector quantity which expresses the distance (in a straight line) between the starting and finishing points.

The two meanings are not the same, as the table shows:

	(a)	(b)
Where are you?	displacement	Position
Where are you relative to the starting point?	Change of displacement	displacement (= change in position)
Velocity	Rate of change of displacement	Rate of displacement