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The coefficient of friction represents the amount of resistance between two surfaces in contact. It quantifies how difficult it is for an object to slide or move across another surface.
Static friction refers to the force that prevents an object from moving when there is no external force acting upon it.
Kinetic friction refers to the force that opposes motion between two surfaces when they are sliding against each other.
The normal force is the perpendicular force exerted by a surface to support an object resting on it.