Resonance and forced Vibration in physics

Force Vibration and Resonance
Let talk about force vibration before we discuss resonance.  From observation the amplitude of vibration in simple harmonic motion never really remains constant but becomes smaller and smaller. For instance the amplitude of bob of a simple pendulum decrease slowly until it comes to a stop. This is caused by loss of energy arising from the viscosity or frictional force between the air and the bob.

In order to maintain an oscillating system in a constant and continuous motion some external periodic force is needed to be applied to the system. For example the simple harmonic motion of a simple pendulum oscillating at its natural frequency will normally be dumped.
However when the bob is subject to an oscillatory external force the frequency is no longer the natural frequency but that of the external force. Such vibration resulting from external periodic force acting on a system is called force vibration

Examples of forced vibration :

  1. Vibration of bridge under the influence of marching soldiers.
  2. Vibration of turning fork when exposed to the periodic external force of wave.3. Also we demonstrate forced vibration in our homes using dinner fork

Resonance
The response of a body to an external force depends on the relation between the forced frequency and the natural frequency.

What is Resonance?

Resonance can be defined as a vibration set up in a body due to transfer of energy from another body which is vibrating with a period or frequency the same or nearly the same as that of the first.

Resonance can also be defined as a phenomenon which occurs whenever a particular body or system is set in oscillation at its own natural frequency as a result of impulses or signals received from some other system or body which is vibrating with the same frequency

Examples of resonance
1.A simple mechanical example of resonance is seen in swing.

Resonance
2. Resonance is also seen in the rattling of windows when a low flying aeroplane passes overhead, especially if natural frequency off vibration of the window happens to be the same as one of the frequencies that make up the noise of the plane’s engine

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