# Damping Theory

### Terminology of vibration mechanics

To evaluate the damping unit requires familiarity with the basic fundamental theory of vibration. Common terminology of vibration mechanics is listed below to assist you in understanding issues related to vibration.

• Free Vibration
• Free vibration takes place when a system oscillates under the action of forces inherent in the system itself and when externally impressed forces are absent. Based on the initial displacement or speed, the kinetic force and the restoring force of the whole system change each other periodically. Therefore, the system moves with simple harmonic motion.
• Natural Frequency(fn)
• Natural frequency is the frequency at which a system naturally vibrates once it has been set into motion. In other words, natural frequency is the number of times a system will oscillate within a period of time between its original position and its displaced position, if there is no outside interference. In a system, the magnitude of natural frequency is equal to the degree of freedom. The frequency of the lowest mode of vibration is called fundamental natural frequency. Two types of natural frequency are most used and listed as follows:
1. Rotational frequency (f): unit is cycle/sec or Hz