Displacement (vector)

In Newtonian mechanics '''displacement''' is one of two subtly different quantities measuring distance and direction
along a path
(a) Displacement in the sense of position vector is a vector quantity which expresses position by 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
(b) Displacement in the sense of movement is a vector quantity which expresses the distance and direction (in a straight line) from the starting to the finishing point
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

By plotting the displacement (relative to the starting point) against time on a position vs. graph] the average velocity or the instantaneous velocity can be found by taking the slope of the graph or the derivative of the graph respectively