Wednesday, January 20, 2016

VIBRATIONS

Vibrations
When a body is held in a position by elastic constraints is displaced from its equilibrium position by the application of an external force and then released, it commences to vibrate. Work done by the external force in producing the initial displacement is against the internal elastic force which resists deformation.
This work is stored up as elastic or strain energy in the constraints so that when the external force is removed, the internal elastic forces tend to restore  the body to its equilibrium position. Neglecting any resistance offered to the motion of the vibrating body for the moment, whole of this elastic or strain energy is converted into kinetic energy at the instant of the body reaches its original equilibrium position. As a result, motion of the body continues until whole of the kinetic energy is absorbed in doing work against the internal elastic forces and energy in the system is once more strain energy. Again the body begins to return to the equilibrium position and oscillations or vibration is repeated indefinitely.

Types of VIBRATIONS
  1. Free or Natural Vibration
  2. Damped Vibration
  3. Forced Vibration
1.  FV/NV:- In these , after the initial displacement no external forces act and motion is maintained by the internal elastic forces.
2. DV:- In these, energy possessed by the system is gradually dissipated in overcoming internal and external resistance to the motion and the body finally comes to rest.
3. FV:- In these, a periodic disturbing force is applied to the body and the vibration has the same frequency as the applied force.


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