This work presents a test rig and the results of experimental investigations of friction force variability in sliding motion under the simultaneous influence of vibrations that are tangential and normal to the sliding plane. Investigations were carried out at the frequency of f = 2000 Hz, which is below the frequency of selfvibrations of the moved object. They were conducted as a function of the three most important factors decisive in the possibility of friction force reduction in sliding motion, and the magnitude of this reduction, i.e. the amplitude of vibrations, amplitude of vibrations velocity, and sliding velocity. Various surface pressures were considered. It has been shown that combining longitudinal tangential vibrations with normal ones increases the individual effects of each type of separately acting vibrations, but it is not directly summing them up.
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