Abstract
Human palmar skin friction and the friction characteristics of common handle materials were investigated under dry and moist conditions. Four male and three female subjects (23 to 41 years of age) were instructed to hold a specially designed pinch dynamometer using a two finger pulp pinch and a constant force of either 19.6 or 39.2 newtons. Pinch force was displayed constantly in view of the subject. An external force, perpendicular to the pinch force, was increased at approximately 15 newtons per second until the dynamometer slipped from the subject's pinch. The coefficient of static friction was calculated as the normal force at the beginning of slipping, divided by two times the pinch force. Seven materials (sandpaper, smooth vinyl, textured vinyl, adhesive tape, suede, aluminum, paper) were studied. Coefficients of friction ranged from for dry paper. The only statistically significant differences with the presence of moisture were for porous materials (adhesive tape, suede, and paper), for which the coefficient of friction increased. The changes with moisture ranged from a 68 percent increase for suede to a 13 percent decrease for sandpaper. The coefficient of friction decreased with increased pinch force for all material moisture combinations. By analysis of variance, the effects of material, moisture, pinch force, subject, and the interaction of pinch force and moisture were all significant at a level of less than 0.01. The pinch force and moisture interaction was significant at a level of less than 0.05. The authors conclude that these data may be applicable to the design of tool handle and work station surfaces.
