INTRODUCTION

In the last chapter, we have discussed the principles of friction of various types. Though these principles have a number of applications in Engineering-science, yet the following are important

from the subject point of view:

1. Ladder friction

2. Wedge friction

3. Screw friction.

LADDER FRICTION

The ladder is a device for climbing or scaling on the roofs or walls. It consists of two long uprights of wood, iron or rope connected by a number of cross pieces called rungs. These runing serve as steps. 

Consider a ladder AB resting on the rough ground and leaning against a wall, as shown in Fig. 9.1. As the upper end of the ladder tends to slip downwards, therefore the direction of the force of friction between the ladder and the wall  (Fw) will be upwards as shown in the figure. Similarly, as the lower end of the ladder tends to slip away from the wall, therefore the direction

of the force of friction between the ladder and the floor (Ff) will be towards the wall as shown in the figure.

Since the system is in equilibrium, therefore the algebraic sum of the horizontal and vertical components of the forces must also be equal to zero.

Note: The normal reaction at the floor (Rf) will act perpendicular of the floor. Similarly, normal reaction of the wall (Rw) will also act perpendicular to the wall.

Equilibrium of the ladder

We know that the maximum force of friction available at the point of contact between the ladder and the floor

Thus we see that the amount of the force of friction available at the point of contact (75 N) is more than the force of friction required for equilibrium (52.1 N). Therefore the ladder will remain in an equilibrium position. Ans.