Coefficient of Friction

Last updated: December 19, 2019

What Does Coefficient of Friction Mean?

The coefficient of friction is a ratio used to quantify the friction force between two objects in relation to the normal force that is keeping them together. The coefficient of friction is an important consideration during material selection and surface requirement determination.


Corrosionpedia Explains Coefficient of Friction

The coefficient of friction can be determined through the following mathematical equation:

μ = FF/FN


  • μ = coefficient of friction
  • FF = friction force
  • FN = normal force

As shown by the equation, both the frictional force and the normal force play a role in determining the coefficient of friction. A higher coefficient of friction means that more friction force is present relative to the normal force. There are two types of coefficients of friction. One is kinetic, which means the object or objects are already in motion; the other is static, which means the objects are at rest.

The friction force is useful for determining the amount of energy loss that will occur between two materials due to friction. For instance, if the contact between two steel substrates results in a friction force, then energy loss due to friction will be high. Depending on the normal force, this could also result in a higher coefficient of friction. If the friction force between a ball bearing and its outer race is low, then the amount of energy loss due to friction will be low. Also, the coefficient of friction will be reduced if the normal force stays the same.

Several methods can be used to increase or decrease the coefficient of friction between two materials. If possible, adjustment to the normal force between two objects can have a large impact on the coefficient of friction. Also, applying coatings to materials can be used to reduce or increase the coefficient of friction between them and also prevent corrosion. Mechanical or chemical surface modification can also have an impact on the coefficient of friction.


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