Saturday, December 26, 2015

frequency - Natural and Resonance frequencies of a damped oscillator


The damped oscillator equation is


m¨x+b˙x+kx=0


And its solution has natural frequency ω0



ω0=km(b2m)2


However, when one adds a driving force to the equation


m¨x+b˙x+kx=Dcos(Ωt+ϕ)


the resonance frequency Ω=ωR that maximizes amplitude is


ωR=km2(b2m)2


I'm wondering why the resonance frequency isn't the natural frequency. I've read this formulas in the wikipedia page of the harmonic oscillator.




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