Introduction:
The static frictional force is a force that comes into play when an object is at rest and is being pushed or pulled. It acts in the opposite direction to the applied force and prevents the object from moving. The force of static friction is dependent on the nature of the surfaces in contact and the magnitude of the applied force.

Example:
Consider a book lying on a table. When we try to push the book, initially it does not move due to the static frictional force. Let's break down the example to understand the different aspects of the static frictional force.

Applied Force:
When we push the book, we apply a force in the direction we want the book to move. This applied force can be from a hand or any other external object.

Opposite Direction:
The static frictional force always acts in the opposite direction to the applied force. In this case, when we push the book towards the right, the static frictional force acts towards the left.

Preventing Motion:
The primary function of the static frictional force is to prevent the object from moving. In the case of the book, the static frictional force between the book and the table surface prevents the book from sliding.

Threshold:
The static frictional force has a threshold value known as the maximum static frictional force. As long as the applied force is below this threshold, the object remains at rest. However, if the applied force exceeds the threshold, the object will start to move.

Dependence on Surfaces:
The magnitude of the static frictional force depends on the nature of the surfaces in contact. Rough surfaces have a greater static frictional force compared to smooth surfaces. If the table and the book have rough surfaces, the static frictional force will be larger, requiring more force to overcome it.

Conclusion:
The static frictional force comes into play when an object is at rest and an external force is applied to it. It acts in the opposite direction to the applied force and prevents the object from moving. The magnitude of the static frictional force depends on the surfaces in contact and the magnitude of the applied force. Once the applied force exceeds the threshold of the maximum static frictional force, the object will start moving.