Question

For making the equilibrium equations for the belt the normal forces that are being acted over them are in which direction in the free body diagrams?

(a) Vertically Upward

(b) Vertically Downward

(c) Horizontally Right

(d) Horizontally Left

This question was posed to me in a national level competition.

The doubt is from Frictional Forces on Flat Belts in section Friction of Engineering Mechanics

Answer 1

Right answer is (a) Vertically Upward

Easiest explanation: As the loads are being acted in the downward direction. Thus to make the forces balance, the normal forces act in the vertically upward direction. As we know that when there is no lubricating fluid present between the surfaces in contact, the dry friction occurs. This friction magnitude is taken out from these normal forces.