Oscillations

When a simple pendulum is pushed through a small distance and observed, we find that the pendulum keeps moving to and fro about its initial position. It moves through its initial position, moves the farthest from there to a maximum height and stops for a few milliseconds(observable) and moves again through its initial position to the other end of the same height(without friction). Thus we can describe the pendulum to be oscillating about it mean position.

Oscillation is a periodic to and fro motion of an object about its mean position. Oscillation is also called as vibration. Another example is shown below.

Spring mass oscillatory
system

The simplest mechanical oscillating system is a mass attached to a linear spring subject to no other forces. Such a system may be approximated on an air table or ice surface. The system is in an equilibrium state when the spring is static. If the system is displaced from the equilibrium, there is a net restoring force on the mass, tending to bring it back to equilibrium. However, in moving the mass back to the equilibrium position, it has acquired momentum which keeps it moving beyond that position, establishing a new restoring force in the opposite sense. If a constant force such as gravity is added to the system, the point of equilibrium is shifted. The time taken for an oscillation to occur is often referred to as the oscillatory period or the time period.