The static friction coefficient, also called the coefficient of friction, describes the relationship between contact pressure or normal force and friction force between two objects. It’s a dimensionless quantity with the help of which the static friction between two objects can be calculated. The value of the static friction coefficient depends on the adhesive and cohesive forces between the active surfaces. Depending on the material, Van der Waals forces or forces akin to hydrogen bridges develop between the surfaces. However, the adhesion is highest for ionic materials.