Using a unidirectional oscillator including a mass-spring system, the authors evidenced the stick-slip phenomena between hard contact surface materials. The sliding friction experiments were realized on the CETR UMT-2 Tribometer at different sliding speeds in dry conditions. The authors have used some models from literature and demonstrate the variation of the kinetic and static friction coefficient during the stick-slip process. According to the authors findings, the kinetic friction coefficient is dependent on the sliding speed and cannot be considered as constant. Also, the authors demonstrate that the static friction coefficient has a continuum variation between a minimum and maximum value, depending on the adhesion time, and Leine’s equation can approximate with high precision these variations.