^Normal reaction, N

^Normal reaction, N

Reaction of net pressing force acting at right angles to the two contact surfaces is called normal reaction.

A pen is resting on a horizontal desk

The force of gravity is pulling down on it, but since it is at rest, it must also be experiencing a force of the desk pushing upward. This force is the normal force, thus N = W.

A body at  rest on an inclined surface.

N = mg cos θ                                       

 

A body pulled up with a force ‘F’ at an angle α to plane.

N = W cosθ – F sin α     

 

A force ‘F’ pressing

a body against a vertical wall.   

N = F