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2 Free Vibration of Single Degree of Freedom System
Fig. 2.1 A water tower model
Fig. 2.2 A portal frame and its freebody diagram
acting on its mass are indicated in Fig. 2.3b. Again in the machine, the forces that
act are the inertia force, the spring force, the damping force and the external force.
From the above examples it is seen, that for studying the vibration of any system,
the following are the four elements of importance:
(a) The inertia force,
(b) The damping force,
(c) The restoring force and
(d) The exciting force.
If the external force is zero, the resulting vibration is called the free vibration. In
such cases, if damping is present in the system, it is called free damped vibration
and if damping is absent in the system, it is called free undamped vibration.