# 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.