\begin{definition}[Definition:Friction/Coefficient/Static]
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 $S$
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:
:$\mu_s = \dfrac F N$
\end{definition}