Some Terms

Periodic motion
A motion that repeats itself in equal intervals of time is called Periodic Motion.

Vibratory motion
If a particle in periodic motion moves back and forth (To and Fro) over the same path, then this type
of motion is called Vibratory or Oscillatory Motion.

Vibration
A complete round trip of a vibrating body is called a Vibration.
or
The motion of a vibrating body from one extreme point to the other
extreme point and back to the first extreme point is called vibration.
For Example the motion of the bob of Simple Pendulum from A to B & back from B to A via point “O” is called one Vibration.

Time period
Time required to complete one vibration is called Time Period of vibrating body. It is denoted by “T”.

Frequency
Number of vibrations executed by a vibrating body in one second is called its frequency.
It is denoted by “f”.
Frequency is reciprocal of time period f = 1/T
Unit of frequency: Hertz
Other units : cycle/sec or vibration/sec.

Displacement
Displacement of the vibrating body at any instant in its distance from the mean
position at that instant either right or left side. Here it is denoted by “x“.

Amplitude
Maximum displacement of a vibrating body on either side of its
equilibrium position is called amplitude of vibration. It is denoted by.