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I'm writing a report at the moment about natural frequency, driving frequency and resonance - and I was wondering, is there a typical % tolerance inside which the driving frequency will cause resonance (or exhibit resonance-like characteristics)? Or does this tolerance depend with the material and construct involved?

(If you have any sources where I can read about this also, it'd be much appreciated).

Note- I'm writing about an oscillatory system - torsion pendulum, so it would be resonance in an oscillatory sense).

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The answer will depend on whether you are considering only simple linear undamped oscillators or more complex cases with damping or non-linear behavior. It might be too much to try to describe every possible outcome so perhaps you should specify a bit more. –  Philip Gibbs Jan 6 '12 at 23:45
    
The system has very (constant) light damping (in order to limit the maximum amplitude of oscillation) but I am considering only the linear behaviour - just interested to see how far from natural frequency an oscillator will begin to exhibit resonance-like characteristics. –  George Pearce Jan 6 '12 at 23:58

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An oscillator is usually characterized by its quality factor Q. This is a dimensionless parameter which measures how "good" of an oscillator it is. It also relates to the quantity you are interested in - a linear, damped oscillator will exhibit a lorentzian peaked response in the frequency domain. The bandwidth of the resonance (points where the response is decreased to 50%) is given by $\Delta f = \frac{f_0}{Q}$.

The quality factor can also be related to the damping coefficient - for more info check out wikipedia: http://en.wikipedia.org/wiki/Q_factor

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Thanks so much! You don't by any chance know of any papers regarding this that I can look up? –  George Pearce Jan 7 '12 at 1:32

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