Friction coefficients in a longitudinal direction between the finger pad and selected materials for different normal forces and curvatures

Abstract

This study investigated the effect of object curvature, normal force and material on skin friction coefficient. Twelve subjects slid their middle fingertip pad against a test object with small (11 mm), medium (18, 21 mm) or large (flat object) radii of curvature, while maintaining a normal force of 1, 10 or 20 N. Tested materials were aluminium and four rubber hoses. The average friction coefficient was 0.6 for aluminium and 0.9 for the rubber hoses. As normal force increased from 1 to 20 N, the average friction coefficient decreased 46%. Friction coefficient did not vary significantly with object curvature. The citation of friction coefficient data requires careful attention to normal force levels with which they are measured, but not so much to object curvature between 11 mm and infinity. This study provides skin friction coefficient data that are needed for design of objects that are manipulated with the hands. The investigation of the effect of object curvature on skin friction coefficient has important implications to ergonomics practices as many objects handled in everyday activities have curved surfaces.

Keywords:

• coefficient of friction
• skin friction
• surface curvature
• skin deformation
• hand friction

Acknowledgements

This project was funded in part by joint funds from the UAW-GM National Joint Committee on Health and Safety and from the National Institute for Occupational Safety and Health (NIOSH) trainee grant. The results presented herein represent the conclusions and opinions of the authors. Its publication does not necessarily imply endorsement by the International Union, UAW, General Motors Corporation or NIOSH.