Sliding friction phenomena have long been the subject of study and modeling. The physical portrayal of the sliding contact upon which such models are based is often a function of the modeler's background, and may range from the atomic scale to the scale of more macroscopic surface roughness. Sometimes, quasi-static arguments are inappropriately applied to sliding situations. The current paper examines the nature of frictional variations during sliding contact. High recording-rate instrumentation was used to analyze detailed, point-to-point variations in friction force for self-mated, pin-on-disk experiments with alumina and aluminum specimens. Data indicate that friction mechanisms, even on a fine scale, must be modeled considering the whole tribosystem, not just the interfacial materials properties alone. The contact conditions stimulate the displacements in the tribocomponents, which in turn result in sensible mechanical output. It is physically unrealistic to develop sliding solid friction models which predict only a single friction value, rather a range of values typical of the variation experienced by the dynamic tribosystem should be developed. A systems approach rather than a discrete asperity approach may ultimately prove to be most productive for modeling tribosystems of engineering interest.Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference In Toronto, Ontario, Canada, October 8–10, 1990