# coefficient of friction

noun
1.
(mechanical engineering) the force required to move two sliding surfaces over each other, divided by the force holding them together. It is reduced once the motion has started
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coefficient of friction in Science
 coefficient of friction   A measure of the amount of resistance that a surface exerts on or substances moving over it, equal to the ratio between the maximal frictional force that the surface exerts and the force pushing the object toward the surface. The coefficient of friction is not always the same for objects that are motionless and objects that are in motion; motionless objects often experience more friction than moving ones, requiring more force to put them in motion than to sustain them in motion. ◇ The static coefficient of friction is the coefficient of friction that applies to objects that are motionless. ◇ The kinetic or sliding coefficient of friction is the coefficient of friction that applies to objects that are in motion. See also drag, friction.
The American Heritage® Science Dictionary