Basic Definitions:

Periodic Motion

The motion that repeats after a regular interval of time is called as periodic motion.

Frequency

In a unit time how much the number of cycles is completed called frequency. Its unit is cycles per second (cps) or Hertz (Hz).

Time Period

Time consume to complete one cycle is called periodic time. It is defined in seconds/cycle.

Amplitude

The maximum displacement of any vibrating system or body from the mean equilibrium position is known as amplitude.

Free Vibrations

While a system is disturbed, it begins vibrating and keeps on vibrating after that without the action of external force. Such vibrations are known as free vibrations.

Natural Frequency

While a system executes free vibrations that are undamped. The frequency of such a system is known as natural frequency.

Forced Vibrations

The vibrations of the system under the effect of an external force are known as forced vibrations. The frequency of forced vibrations is equivalent to the forcing frequency.

Resonance

While frequency of the exciting force is equivalent to the natural frequency of the system it is known as resonance. Under such conditions the amplitude of vibration make up dangerously.

Degree of Freedom

The degree of freedom of any vibrating body or system implies the number of independent coordinates that are needed to define the motion of the body or system at given instantaneous.