What actually is natural frequency?

[kapil phyreak]

when we talk about the phenomenon of resonance, we use the term 'natural frequency'. What actually is natural frequency of an object?...what is meant by matching of natural and applied frequency and why does it produce vibration with maximum amplitude?

 

[bp_psy]

when we talk about the phenomenon of resonance, we use the term 'natural frequency'. What actually is natural frequency of an object?...what is meant by matching of natural and applied frequency and why does it produce vibration with maximum amplitude?

The natural frequency is the frequency at which some system will oscillate if it is not forced. If you just pull a mass spring system a small distance and then release it. It will oscillate at its natural frequency.

If you force a damped oscillator with some sinusoidally varying force it will oscillate at the frequency of the force not the natural frequency.This makes sense since if I shake the spring around it will not move as if it was free.
The Amplitude of oscillation is greatest when the driving force frequency is near the natural frequency, since at that point the the energy that can be stored in system is the greatest.