Final answer:
The coefficient of friction (C) is a dimensionless value representing the ratio of frictional force to the normal force between two contact surfaces. It reflects the combined effects of surface roughness and molecular forces (A) and determines the force required to overcome friction (D). It is not the resisting force itself (B), but a factor in calculating this force.
Step-by-step explanation
Description of Coefficient of Friction
The coefficient of friction is best described as the ratio of frictional force to the normal force (C). This concept illustrates how the force required to overcome the friction between two surfaces depends on the roughness and nature of the surfaces in contact as well as the amount of normal force pressing them together. The coefficient of friction is a dimensionless constant that reflects the combined effects of the microscopic roughness and the molecular forces of the materials in contact (A). It dictates how much force is needed to initiate and maintain motion, demonstrating the amount of resistance imposed by frictional forces (D). The force resisting the motion of two surfaces in contact (B) is not the coefficient itself but is influenced by it.
Friction itself is a resistive force that opposes the relative motion or the tendency toward motion of two objects in contact. Frictional forces, which are always acting opposite to the direction of motion, arise due to both the microscopic roughness of surfaces and molecular attractive forces between the materials in contact. Therefore, to calculate the frictional force, one must consider both the nature of the substances and the force with which they are pressed together (the normal force). For example, a higher coefficient of static friction would require a larger force to initiate the motion of an object.