Friction noise of human skin in vivo

The feeling of smoothness during the touch is delivered when the finger is rubbed on the surface. A static contact cannot provide such information. The friction noise generated during the sliding of two rough surfaces, is therefore the key phenomenon for the feeling of smoothness. In this purpose, a tribo-acoustical probe has been developed. This is a kind of artificial finger with a controlled load equipped with a microphone that measures the sound pressure level. When rubbing the probe on various surfaces, it is possible to compare the acoustical level and therefore to assess the relative smoothness of the surfaces. Most of works in literature tried to assess the softness of surfaces by the measurement of the friction coefficient only. This work shows well the major contribution of adhesion and contact area which influence the friction force, while friction noise gives a signature of softness.