A force which resists to change it is state of rest of an object is called static friction. When you tend to move an object along a surface, up to certain quantum force, the object doesn’t move. This is because the object tends to be static and tries to oppose any force that’s trying to disturb it is static condition. The opposing force is called static friction. It is denoted as Fs. The static friction is so common that the general term friction refers to static friction. . Look at the above diagram. An object of mass “m” is placed on a table and a string is attached to it which passes through a pulley in such a way that weights can be hung vertically. With a little weight, which tends to slide the object, the static friction Fs exerted by the table on the object is more than the force F1 that’s applied to the object due to the weight supported by the string. With gradual increase of weights on the string, at one stage, the object just starts sliding. At this condition, the force F2 applied on the object just balances the static friction Fs The limiting value of the force to at which the metal block starts moving is equal to the resistive force offered by the metal block under static condition. Hence that resistive force is called static friction. The force of sliding friction is directly proportional to the load acting in the direction normal to the surface. In a particular case (as shown in the above diagram), if the surface on which the object slides is horizontal, then the normal force equals the weight of the object. Imagine the following situation. A heavy crate is resting on the floor in a warehouse. You push it horizontally with a steady force, except it doesn’t move. That’s because the force that you apply is balanced by a frictional force exerted horizontally on the bottom of the crate by the floor and opposite to the direction of your push. Remarkably, this frictional force automatically adjusts itself, in both magnitude and direction, to cancel exactly whatever force you decide to apply. Of course, if you push hard enough you will be able to move the crate.