When an object at rest is pushed on a surface, due to the interlocking of the rough surfaces, static friction is generated. This frictional force resists the applied force and does not allow the object to move and hence it is known as the Static frictional force. The static friction depends on the coefficient of friction of the surface of contact and the normal force acting on the object by that particular surface. Therefore, for an object to get into motion from rest, it has to overcome the static friction acting against it.
Example 1: Calculate the amount of static friction acting on an object of mass 2kg placed on a horizontal surface if the coefficient of static friction is 0.24.
Static friction, fs = μs * N
Here, μs= coefficient of static friction = 0.24
N = Normal force= Weight of the object= (mass) * (gravity) = 2kg * 9.8m/sec2 = 19.6N
So, fs = 0.24 * (19.6) ==>fs =4.7N
Therefore the static frictional force acting on the object, fs = 4.7N
Example 2: If the coefficient of maximum static friction of the surface on which an object is placed is 0.72, then how much amount of force is needed to move the object of mass 8kg from rest?
Static friction, fs = μs * N
Here, μs= coefficient of static friction = 0.72
N= Normal force= Weight of the object = (mass) * (gravity) = 8kg * 9.8m/sec2 = 78.4N
So, fs = 0.72 * (78.4) ==>fs = 56.45N
Therefore the maximum static frictional force required, fs = 56.45N