Limiting coefficient of static friction

Definition

Given two surfaces, the limiting coefficient of static friction between them, denoted $\mu_s$ or $\mu_l$, is defined as the number such that the static friction between any two bodies with these two surfaces respectively as the surfaces of contact cannot exceed $\mu_sN$, where $N$ is the normal force between the two bodies.

The notion of limiting coefficient of static friction arises as part of the Coulomb model of friction.

Units and dimensions

The limiting coefficient of static friction is a dimensionless scalar and does not need units.

Range of values

The limiting coefficient of static friction typically takes values in the range of $0.2$ to $0.6$. In most cases, the limiting coefficient of static friction is less than $1$, but there could be situations where it is greater than $1$. For very slippery surfaces, the limiting coefficient of static friction may be less than $0.1$.

Measurement

The limiting coefficient of static friction must be determined empirically, though measurement. Because a lot depends on the specific surfaces, the measurement may vary due to factors such as dampness, scratches, or minor changes to the surface.