The ratio of the force that maintains contact between an object and a surface and the frictional force that resists the motion of the object; the ratio of two forces acting, respectively, perpendicular and parallel to an interface, between two bodies under relative motion (Blau (2001) Tribology Int. 34, 9). Under the same friction coefficient different normal stresses cause different friction levels (Kame and Yamashita (2003) Geophys. J. Int. 155, 3). In a rockfall, the friction coefficient is the strongest factor in determining velocity (Dorren (2003) PPG27, 1). See also Smith et al. (2007) PPG31, 4.
Subjects: Earth Sciences and Geography.