Book on a Desk ‒ Friction

Friction is a phenomenon which arises during movement of the physical body in close contact with another physical body. With friction the frictional force *F*t occurs, which always works against the direction of the movement.

The model is a book lying on the table attached via a pulley and fixed to a set of weights. The weights affect the book and cause the book to shift. The frictional force between the surface of the book and the work surface works against the movement.

Detail of the friction surfaces shows molecular composition of both materials. The work required to overcome the frictional force changes by friction into the internal energy, which is manifested as an increase in the temperature.