## Fundamentals of Physics Extended (10th Edition)

$f_{s}$ is greatest with force 1, then force 2, and its the smallest with force 3.
Because the block remains stationary, the forces on it must be equal and opposite. This means that what ever force is applied to it in one direction, it will be matched by the $f_{s}$ in the opposite direction. Force 1 is the greatest, so the $f_{s}$ is greatest in that experiment. Force 3 is the smallest, so $f_{s}$ is the smallest in that experiment.