# Get to Know How to Calculate the Coefficient of Kinetic Friction

What is the kinetic friction coefficient? How is it calculated? Read to find all the answers.

ScienceStruck Staff

Last Updated: Jul 22, 2017

What is Kinetic Friction?

Friction is the macroscopic force that opposes relative motion between any two surfaces, at the point of contact. The surfaces might be a solid and a fluid, two fluids, or a solid-fluid interface. When the two surfaces in contact are solids, it's called 'Dry Friction', for reasons that are self-explanatory.

The Coefficient

Dry friction has been theoretically modeled in physics so that it can be quantified. This coefficient is a concept that emerges in its empirical theory. The perpendicular force between two surfaces in contact with each other is called the normal force. The Coulomb theory of kinetic friction is based on the following equation:

F

_{f}= μ_{Kinetic}F_{N}_{Kinetic}is the coefficient of kinetic friction, F

_{f}is the frictional force and F

_{N}is normal force between the two surfaces. As one can deduce from the equation above, kinetic friction coefficient is the ratio between the frictional force exerted between the two surfaces and the normal force between them. Being a ratio, it has no units.

Calculation

From the equation above, one can derive:

μ

_{Kinetic}= F_{f}/F_{N}