What is Coefficient of friction (COF)?
Coefficient of Friction is a common unit of measurement used to characterize the slip retardance of a surface. The COF of two surfaces is the ratio of the horizontal (or lateral) and vertical (or normal) forces required to move one surface over another surface to the total force pressing the two surfaces together. The most common apparatus for evaluating surface materials is the James Machine (referred to in ASTM D 2047), used to measure polish-coated surfaces. It is a popular test method, but not mobile for on-site testing. The reproducibility of the instrument makes it valid only for testing dry, smooth, polish-coated surfaces. The James Machine is referred to as a time-delayed device because after a weight is applied through a strut (typically with a leather sensor) and placed on a flooring sample — the sample and the sensor are moved horizontally until the sensor slips on the sample. Several new testing apparatus are being developed that apply the weight and the angle of slip at t
