Full definition
The dimensionless ratio of the friction force between two surfaces to the normal (perpendicular) force pressing them together: μ = F_friction / F_normal. COF is the fundamental parameter governing: belt drive capacity (effective μ in V-belt grooves determines maximum transmittable power per the Euler equation), flooring safety (static COF ≥0.5 per ASTM D2047 = non-slip classification), conveyor belt traction (drive drum lagging COF determines belt tension limits), and seal friction (determines actuation force and energy loss in hydraulic cylinders). Types: static COF (force to initiate sliding — always higher) and dynamic/kinetic COF (force to maintain sliding). For V-belts: effective μ is multiplied by 1/sin(α/2) due to the wedging action in the groove, increasing the effective value from ~0.5 to ~1.5-2.5. Typical COF values: rubber on steel 0.5-0.8 (dry), V-belt in groove 1.0-2.0 (effective), rubber flooring on leather shoe 0.5-0.9, PTFE on steel 0.04-0.10, lubricated steel on steel 0.05-0.15. Measurement: ASTM D2047 (flooring), ASTM D1894 (films/sheet), and ASTM G115 (general). Per ASTM and ISO friction test methods.