14.9 Damped Oscillation
The oscillations with decreasing amplitude in the presence of various resistive forces are called damped oscillations and the resistive forces are called damping forces.
In an ideal free oscillation system, we have studied that the total mechanical energy of the oscillating body remains constant, as we discussed in mass spring system, motion of a body in a circle and also in case of a simple pendulum. But in practical life, as we observe daily, some dissipating forces such as air resistance, friction, etc. The amplitude of the oscillation gradually decreases with time due to these forces and finally it comes to rest.
For example, a girl is swinging on a swing as shown in Fig. 14.14. Damping occurs and the swing will oscillate with smaller and smaller amplitude and eventually stops. Graphically the damped oscillation of the oscillating body is shown in Fig. 14.15. Similarly, the amplitude of oscillating simple pendulum decreases gradually with time till it become zero and touching an oscillating tuning fork with our finger are examples of damped oscillation.
(Fig. 14.14: Damped oscillation of swing)
(Fig. 14.15: Graphical representation of damped oscillation)
Interesting Information
lightbulbLight damping: It reduces gradually the energy and amplitude of vibrating body. A swing in playground is the best example of light damping.
Heavy damping: It is a type of damping which takes longer time before the body comes to a rest. For example, a pendulum submerged in thick oil experiences a heavy resistance from oil.
Critical damping: It is a type of damping in which object returns to equilibrium position in the shortest possible time, e.g., shock absorbers in a car.