Normal force is the force exerted on an object perpendicular to the surface of contact. When an object is placed on the ground, there is a constant downward pull of the earth on the object which is known as the ‘gravitational force’. According to Newton’s third law of motion, this gravitational force on the object is balanced by the force in the opposite direction, known as the Normal force and this force acts perpendicular to the surface of contact on which the object is placed.
Example 1: Calculate the normal force acting on an object of mass 3kg placed on a horizontal surface.
Given: mass of the object, m = 3kg
The gravitational force acts in the downward direction on the object= Weight of the object = (mass * gravity)
Here gravity is a constant= 9.8m/sec2==>Weight= (3kg) * (9.8m/sec2) = 29.4N
Since the surface of contact is a horizontal surface, hence the normal force on the object acts straight
upward balancing the weight of the object acting downward.
Therefore, Normal force= Weight of the object = 29.4N
Example 2:If the normal force acting on an object placed on a horizontal surface is 68.6N, then calculate the mass of the object.
Given: Normal force acting on the object = 68.6N
Normal force = Weight of the object = (mass) * (gravity)
68.6 = m * (9.8m/sec2)
This gives: mass, m = (68.6)/ (9.8) = 7kg
Therefore, mass of the object, m = 7kg.