[applestrudle]

Does resonance only occur in an undamped system when the driver frequency is equal to the natural frequency or can it occur also in damped systems?

In damped systems is it when the amplitude is maximum? And how can this be resonance if the energy is being dissipated (due to unefficient transfer)?

Thank you

[Stonebridge]

Resonance occurs whether or not the system is damped. No real mechanical system is undamped.
The greater the damping the smaller will be the amplitude of the resonant vibration.
It's also true that as the damping gets larger, the damped resonant frequency falls below the value of the "natural" (undamped) resonant frequency.