General Force Measurement
Coefficient of Friction Testing

Coefficient of Friction (COF) is the maximum value of the frictional force divided by the normal force.  COF is used in a variety of materials from lubricants, to films to household items (ceramic tile) to determine the frictional characteristics of a material.  It is generally determined to be the ease by which two surfaces (often of different materials) slide against each other.  The dimensionless value of the COF is the ratio of the force required to slid the surface to the force perpendicular to the surface.  A low COF indicates that the surfaces are "slicker", e.g. less resistant to a sliding motion.  Polymers used for film production are usually tested dry against a sled with a calibrated load.

A distinction is made between the static COF (at the point of incipient motion) and the dynamic COF (measured at constant velocity).  The difference between the static and dynamic COF is sometimes known as "slip stick".  A polymer with a low "slip-stick" are often associated with products used in a back-and-forth or stop-and-go movement.

Common results available from Chatillon^® system  for COF are:

• Static friction
• Kinetic friction

Common industry standards for determining COF are:
- ASTM D-1894
- ASTM D-1055
- ASTM D-5095

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