$A$ 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 $F$.

(N/A) The graph of frictional force $f$ versus applied force $F$ is shown in the figure.
$1$. The part $OB$ of the graph represents the static friction region. In this region,the frictional force is a self-adjusting force,meaning $f = F$. The slope of this line is $1$.
$2$. Point $B$ represents the limiting friction,which is the maximum value of static friction $(f_{s,max})$.
$3$. Once the applied force exceeds the limiting friction,the block starts moving. The region $CD$ represents kinetic friction $(f_k)$. Kinetic friction is generally constant and slightly less than the maximum static friction.