An analytical model was developed for the dynamic sliding friction of polytetrafluoroethylene (PTFE) samples on a dry glass surface as a function of the angle of inclination. The analytical expression was derived as a function of the contact area and the built-up film of debris particles caused by wear, and was compared with the velocities experimentally determined from the samples as a function of the sliding length. The velocity greatly increased in the initial stages of sliding, reached a maximum value in the middle stages, and then significantly decreased in the later stages. The model predicted all of the important qualitative features of the velocity change and suggested that the increase in the velocity in the initial stages of sliding can be explained by acceleration due to gravity, whereas the decrease in the middle and late stages was attributed to increasing contact area and the build-up of debris particles.
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