Please could someone explain the concept in the text below for me?
In a driven oscillator, the phase of the driver and the phase of the oscillator are not always the same. At low frequency ($\omega\ll\omega_0$) the oscillation is in phase with the driver. At high frequency ($\omega\gg\omega_0$) the oscillation and the driver are out of phase. The phase difference between the driver and the oscillator is given by: $$\phi(\omega)=\arctan\left( \frac{-\gamma\omega}{\omega_0^2-\omega^2}\right). \tag{1.6}$$
If the oscillator is in phase with the driver at low frequency then surely this would cause the oscillator to resonate, but there should only be one frequency(the natural frequency)that can achieve resonance? I think I am confusing things here...please help! Thanks in advance.