The resonance frequency and the damping behaviour of a vibrating cantilever as used in dynamic Scanning Force Microscopy (SFM) is investigated with the frequency modulation (FM) technique. The properties of a silicon-cantilever/tip vibrating in front of a silicon surface were studied under UHV conditions as a function of the tip-sample distance. The experimental results are compared with a computer simulation. The different characteristic parts of the experimental curves can be interpreted in terms of attractive and repulsive forces acting on the cantilever as well as the behaviour of the amplitude control electronics. Using the computer simulation noncontact regimes can clearly be distinguished from intermittent contact regimes.