Vibrations are oscillations of a system about an equilibrium position

We Experience Vibration Everyday

It is also a phenomenon we meet in our everyday lives

Effects of Vibration

Compressor

Testing

Basic Definitions

Periodic Motion:

A motion that repeats itself  after an equal interval of time

Time  Period: 

Time is taken for one complete cycle

Simple Harmonic Motion:

Motion of particle

Basic Definitions

Amplitude (Z or 2Z): The maximum displacement of a  vibrating body from its mean position. The amplitude can either be single amplitude (Z) when the distance from mean position to maximum displacement is measured or double amplitude (2Z) when the distance from negative maximum to positive maximum displacement (motion) is measured.

Frequency: It is the number of cycles per unit time.  Frequency and time period are inversely proportional to each other. A vibratory motion can have either a very high frequency or a very low frequency. Frequency can be expressed either as angular (circular) frequency (ω) or oscillatory frequency (f). ω is expressed in radians per second and f is expressed in cycles per second or Hertz.

free vibration: Vibration of a  system because of its own elastic property. No external force is required for this vibration and the only initiation of vibration may be necessary.

Forced Vibration: A System that vibrates under an external force at the same frequency as that of the external force

Natural frequency: It is the frequency of free vibration of a system. It is constant for a system. In fact, it is an inherent property of a system.  It depends on the elastic properties, mass, and stiffness of the system.

Resonance: Vibration of a system when the frequency of external force is equal to the natural frequency of the system. The amplitude of vibration at resonance becomes excessive. During resonance, with minimum input, there will be a  maximum output. Hence both displacement and the stresses in the vibrating body become very high.