\mathbf{G}
= \frac{-k \left( \frac{\omega}{\omega_0} \right)^2}{
   1 + \frac{j}{Q} \frac{\omega}{\omega_0}
   - \left( \frac{\omega}{\omega_0} \right)^2}
= \frac{-k \left( \frac{f}{f_0} \right)^2}{
   1 + \frac{j}{Q} \frac{f}{f_0}
   - \left( \frac{f}{f_0} \right)^2}