Free, Forced and Damped Oscillation

Free Oscillation:

Difinition:       “The oscillation of a system which occurs without the interference of external force are called free Oscillation”.

  1. The free oscillation possesses constant amplitude, period, frequency and energy without any external force to set the oscillation.
  2. Ideally, free oscillation does not undergo damping. But in all natural systems damping is observed unless and until any constant external force is supplied to overcome damping.

Example:

            A simple pendulum vibrates freely with its natural frequency “fo” and time period “T”, that  depends only upon length when it is slightly displaced from its mean position.




Forced Oscillation:

Difinition:       “The oscillation that occurs under the influence of some external periodic force are known as forced Oscillation”.

Examples:

  1.  When a swing is disturbed repeatedly with a periodic force, then its vibration become forced vibration or oscillation.
  2. The oscillation of the factory floor caused by the running of heavy machines is due to forced oscillation.
  3. When the bob of the pendulum during oscillation is struck repeatedly produced forced oscillation.
  4.  When the prongs of the vibrating tuning fork be held over the open end of resonance tube produces forced oscillation of the air column in the tube.
  5.  The string instrument causes forced oscillation of wooden board by producing loud sound.

 

Damped Oscillation:

Definition:      “The oscillation that fades with time is called damped oscillation”.

  1. The damping is a resistance offered to the oscillation.
  2. Due to damping, the amplitude of oscillation reduced with time.
  3.  Reduction in amplitude is a result of energy loss from the system in overcoming external forces like friction or air resistance and other resistive forces.

There are two types of damping:

  •                        Natural damping
  •                       Artificial damping