Friction depends on how hard the two surfaces press against each other.

Suppose your writing desk is tilted to a position where a book kept on it just starts sliding down. The figure, showing the correct direction of frictional force acting on it, is-

Two boys are applying oppositely directed, and equal in magnitude, forces on a box as shown in the figure. 

In such a case, the force of friction, that would exist between the lower end of the box and the ground, would be called?

Four students were asked to arrange the (frictional) forces, due to rolling, static and sliding friction, in an increasing order. Their arrangements are listed below. The correct arrangement is —