Effects of the tip induced nonconservative atomic processes on the cantilever dynamics of dynamic-mode atomic force microscopy are theoretically analysed on the basis of the time averaging perturbation theory. Atomic adhesion is considered as an example of nonconservative process. Typical magnitude of the Q value due to adhesion is estimated to be of the order of 10⁴, which is comparable to the intrinsic Q value of the cantilever. The additional frequency shift due to adhesion is estimated to be of the order of 10 Hz, which sets in suddenly when the tip turning point becomes less than a certain threshold height. This feature explains the experimental observation of the discontinuous frequency shift at chemical reactive sites on the semiconducting surface.