How to explain the physics of phase lag due to viscosity damping in forced vibration?

1. Oct 23, 2012

d9052492

Dear all,

Can anyone explain the the phase lag between force and displacement in single degree of freedom forced vibration with viscosity damping?

The response of phase angle derived by mechanical vibration as below ( assuming force is excited harmonically) :

Phi(ω) = arctan( C*ω / ( K - M*ω^2 ) )

Where Phi is the phase angle function, C is damping, K is stiffness, M is mass, and ω is angular frequency.

From the function above we know that as C is not zero, the phase angle varies with angular frequency, but as C is set to be zero, the phase angle will be constant until K - M*ω^2 equals to zero ( the frequency also known as resonance frequency ). My question is how to explain the phase angle varies with frequency by a physical view ?