Which of the following is a self-adjusted force?
Static friction is considered a self adjusting force because it wants the objects to remain at rest. If an external force is applied, the static friction force will equal the magnitude of the applied force, until it surpasses the threshold of motion.
Suppose we are pushing a block placed on a surface. It does not move. The force we are providing is exactly equal to the frictional force provided by the surface. If the applied force is increased the frictional force also increases automatically to balance it. The block remains at rest. The static frictional force by itself increases by the exact amount required to balance the applied force, before the motion starts. This happens until the frictional force value reaches its maximum. Hence, before any relative motion between the surfaces begins, the frictional force is a self-adjusting force.