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Please explain the coefficient of friction. Thank You

What level of explanation do you want? The coefficient of friction is an empirical rule that is associated with the force required to move one object rubbing against another relative to the force with which the two objects are being pressed together. The rule is that the required force for motion is linearly proportional to the normal force, and the ratio between the two is the coefficient of friction (always between 0 and 1). There are different coefficients for different types of motion - there is a coefficient to get the motion started, and another to keep it going, and yet another associated with "rolling" as opposed to sliding. Friction comes from the electrical interactions between the two surfaces at the level of the atoms and molecules, and can often be significantly reduced by interposing a liquid (a lubricant) between the two surfaces, because then the upper surface slides on a layer of lubricant which can move freely over the other layer of lubricant attached to the lower surface.

Arthur Smith

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