Friction is a force that prevents some sliding objects from moving. We can find friction in our surroundings at any time. It acts in a direction opposite to that of the object's movement. We can stop quickly if we run down the sidewalk and slow down and then eventually stop because of the frictional force between our footwear and the ground. Friction can occur with either a moving or stationary body. As a result, it can be both dynamic and static.
What is Static Friction?
Friction occurs when people attempt to move a non-moving object on the ground without actually causing any displacements among the surfaces.
Ever observed how much more difficult it is to get a shopping trolley travelling than to keep moving? When attempting to push a bed or sofa across one corner, the very first push is the most difficult. People may believe that it is purely psychological, but there is a physical reason for it. This happens because of static friction.
In other words, static friction can be defined as the force that keeps an object at rest.
Static Friction Formula
Fs = μs × Fn
where,
- μs is static friction coefficient
- Fn is normal force acting upon the object.
Examples on Static Friction
Example 1: Determine the static friction acting on a couch of 7 kg, given the force applied, is 45 N and the coefficient of friction is 0.6. (Take g = 9.8 m/s2)
Solution:
Given:
Weight of Couch = 7 kg
g = 9.8 m/s2
Fn = 7 × 9.8 N
= 68.6 N
μs = 0.6
Since, Fs = μs × Fn
= 0.6 x 68.6 N
= 41.16 N
Thus, the friction force applied is 41.16 N
Example 2: Determine the static friction acting on a table of 10 kg, given the force applied, is 200 N and the coefficient of friction is 0.7. (Take g = 9.8 m/s2)
Solution:
Given:
Weight of Table = 10 kg
g = 9.8 m/s2
Fn = 10 × 9.8 N
= 98 N
μs = 0.7
Since, Fs = μs × Fn
= 0.7 x 98 N
= 68.6 N
Thus, the friction force applied is 68.6 N
Example 3: Find the coefficient of static friction if an object is being pushed from a state of rest by applying a force of 500 N and the static friction acting on it is 250 N.
Solution:
Given:
Fs = 250 N and Fn = 500
Since, Fs = μs × Fn
250 = μs x 500
μs = 250/500
μs = 0.5
Example 4: Determine the static friction acting on an object of mass 50 Kg, given the force applied, is 1000 N and the coefficient of friction is 0.4.
Solution:
Given:
Weight of Object = 50 kg
g = 9.8 m/s2
Fn = 50 × 9.8 N
= 490 N
μs = 0.4
Since, Fs = μs × Fn
= 0.4 x 490 N
= 196 N
Thus, the friction force applied is 196 N