The limiting friction is

Write the unit of the coefficient of static friction.

Which of the following is true about the coefficient of static friction $(\mu_s)$ and the coefficient of kinetic friction $(\mu_k)$?

$A$ block placed on a rough horizontal surface is pulled by a horizontal force $F$. Let $f$ be the force applied by the rough surface on the block. Plot a graph of $f$ versus $F$.

$A$ body of mass $m$ is kept on a rough horizontal surface (coefficient of friction $= \mu$). $A$ horizontal force is applied on the body,but it does not move. The resultant of the normal reaction and the frictional force acting on the object is given by $F$,where $F$ is:

$A$ block of mass $m$ lying on a rough horizontal plane is acted upon by a horizontal force $P$ and another force $Q$ inclined at an angle $\theta$ to the vertical. The minimum value of the coefficient of friction between the block and the surface for which the block will remain in equilibrium is