What is the cause of friction? Explain with the help of a labelled diagram.

The cause of friction is surface roughness and adhesion.

When we apply force, F on a book, the book slide (Fig A). Then acts a force of friction, f (Fig B)

The friction is produced due to the contact of the two surfaces of the table and the book. It acts in opposite direction of the force to stop it. And, we see after some distance, the book again comes to the rest (Fig C).