# Coulomb's law of friction

## Name

This law is termed Coulomb's law of friction and is also sometimes referred to as Amontons' third law of friction.

## Statement

The law states that for two dry solid surfaces sliding against one another, the magnitude of the kinetic friction exerted through the surface is independent of the magnitude of the velocity (i.e., the speed) of the slipping of the surfaces against each other.

Note that the direction of the kinetic friction does depend on the direction of the velocity -- it is precisely the opposite direction.

Coulomb's law of friction is part of the Coulomb model of friction, a model for the behavior of frictional forces between two dry solid surfaces in contact.

## Related facts

• Amontons' first law of friction: This states that the magnitude of the friction force is independent of the area of contact between the surfaces.
• Amontons' second law of friction: This states that the magnitude of the friction force between two bodies through a surface of contact is proportional to the normal force between them. A more refined version of the statement is part of the Coulomb model formulation of friction.