Coefficient of Friction (COF) defifines the sliding interaction between two surfaces. Static Friction and Dynamic Friction (or Kinetic Friction) are defifined in many standards including GB10006, ASTM D1894, ISO8295, ISO15359, GB/T22895.
The co-effiffifficient defifines the sliding resistance of two surfaces, such as a ski on snow (A), or feet on grass (B). In the absence of friction, the effffort needed to slide an object would be signifificantly reduced, as would the effffort needed to stop or change direction.
Newton’s fifirst law of motion states that a body remains at rest or in uniform motion unless acted upon by a force. Gravity causes a mass to press down with a force equal to its mass multiplied by acceleration. It follows that friction is the force needed to start sliding an object (Static Friction), or the force needed to keep it sliding (Kinetic Friction), expressed as a ratio by dividing into the downward force of the mass.
In industrial applications it can be important to understand how two surfaces interact with one another, e.g. flflexible plastic fifilm sliding over pouch formers in a highspeed packaging machine, or paperboard cartons being drawn into an erector then later stacked on top of one another. Things can go wrong when the interaction is not constant. In automated processing, adjustments made to dynamic machinery only work when the material reacts the same way each time. When replenishing a roll of flflexible plastic fifilm on a high-speed packaging line, fifilm that exhibits difffferent friction may not run smoothly, potentially causing alignment, snagging and running problems.
