Page 19 - 11-phy-7 Oscillations

7. OSCILLATIONS eLearn.Punjab

7.7 FREE AND FORCED OSCILLATIONS Comparison of SHMs

A body is said to be executing free vibrations when it oscillates
without the interference of an external force. The frequency
of these free vibrations is known as its natural frequency. For
example, a simple pendulum when slightly displaced from its
mean position vibrates freely with its natural frequency that
depends only upon the length of the pendulum.

On the other hand, if a freely oscillating system is subjected
to an external periodic force, then forced vibrations will take
place. Such as when the mass of a vibrating pendulum is struck
repeatedly, then forced vibrations are produced.

A physical system under going forced vibrations is known
as driven harmonic oscillator

The vibrations o f a vehicle body caused by the running of Animation 7.10: Free and forced oscillations
engine is an example of forced vibrations. Another example Source & Credit: f-lohmueller
of forced vibration is loud music produced by sounding
hollow wooden parts of string instruments.

7.8 RESONANCE

Associated with the motion of a driven harmonic oscillator, there is a very striking phenomenon,
known as resonance. It arises if the external driving force is periodic with a period comparable to
the natural period of the oscillator.

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