Suppose a body is moving along a straight line. Let the straight line is along x – axis. Let at a time t1 it was situated at point A at a distance x1 from a fixed point O. Let it moves & at time t2 reaches point B situated at a distance x2 from O.
Here the distance AB is called displacement of the body along x axis (Sx) in the time interval t2 – t1 (= Dt). In terms of position coordinates it can be expressed as
Displacement, AB = OB – OA = x2 – x1 or Δx.
i.e. for motion along displacement is equal to the change in position coordinates along that line.