Category:Definitions/Coefficients of Friction

This category contains definitions related to Coefficients of Friction.
Related results can be found in Category:Coefficients of Friction.

Let $B$ be a body at rest on a plane surface $S$ on which friction acts.

Let $N$ be the normal reaction of $S$ on $B$.

Let a force be applied to $B$ parallel to $S$.

Coefficient of Static Friction

Let $F$ be the magnitude of that force in the limiting case when $B$ is just about to move.

Then the coefficient of static friction is defined and denoted:

$\mu_s = \dfrac F N$

Coefficient of Kinetic Friction

Let $F$ be the magnitude of that force needed to keep $B$ moving at a constant velocity.

Then the coefficient of kinetic friction is defined and denoted:

$\mu_k = \dfrac F N$

These coefficients of friction depend upon the materials out of which $B$ and $S$ are made.

It is usual for $\mu_s$ to be greater than $\mu_k$.