Displacement : The distance of the oscillator (simple harmonic body means oscillator) at any instant from the equilibrium (fixed or reference point) position is called displacement of the oscillator at that instant.
The displacement is considered positive from one side of equilibrium point and negative from other side. In short, displacement prossess zero, positive and negative values.
Displacement is refers to change with time of any physical property under consideration. Its examples are as follow :
(1) In case of rectilinear motion of a steel ball on a surface, the distance from the starting point as a function of time is its position displacement. The choice of origin is a matter of convenience.
(2)
Consider a block attached to a spring, the other end of which is fixed to a rigid wall, as shown in figure (a). The block moves on a frictionless surface.
The motion of the block can be described in terms of its distance or displacement x from the wall.
(3) In figure (b), an oscillating simple pendulum. its motion can be described in terms of angular displacement `theta` from the vertical.
For an oscillating simple pendulum, the angle from the vertical as a function of time may be regarded as a displacement variable.
(4) The displacement variable may be taken in pressure variations with time in the propagation of sound wave in air.
(5) The displacement variable may also take in the changing electric and magnetic fields in a electromagnetic waves.
(6) The voltage across a capacitor, changing with time in an a.c. circuit is also a displacement variable.
Hence, it is not so that the displacement variable always taken as in the context of position but above shown displacement variable may be taken.
