Abstract:

The relationship between the coefficient of dynamic friction and related perceived discomfort, and the effect of oil, lard and sweat on various textured as well as nontextured surfaces were investigated. Fourteen men served as study subjects. Twelve of them performed office jobs, two performed daily light industrial work in a model shop. The subjects applied forces of 1, 10 or 20 newtons (N) using the index finger of the dominant hand while striking across a specimen of a ridged polycarbonate material with 100, 75, 50, or 25% skin contact area. Surface pressures were in the range of 6 to 299 kilopascals. A very low correlation was noted between the coefficient of dynamic friction and perceived discomfort. Discomfort was associated with wider grooves and increased normal forces. However, these did not provide more friction. Palmar skin showed sticky characteristics and the coefficient of dynamic friction often was greater than 1.0 when the surface loads were low. Increasing surface loads resulted in a lessening of the coefficient of friction on palmar skin. When the normal force increased, a considerable reduction of the coefficient of dynamic friction was noted. Increasing the normal force from 1 to 20N resulted in an eight fold increase in frictional force while the coefficient of dynamic friction dropped from 2.22 to 0.85. Grooves in surfaces reduced the coefficient of dynamic friction under normal and sweaty conditions, but improved the coefficient of dynamic friction when contaminants were present. When the skin was exposed to paraffin oil, the coefficient of dynamic friction decreased drastically to 0.28. Oil and lard reduced the coefficient of dynamic friction, but sweat increased it in relation to a normal hand.