Question

If the normal force acting on a block laying on a horizontal plane is made four times then the coefficient of friction will become,
A) Four times.
B) Half of the initial value.
C) Eight times the initial value.
D) Remains the same.

Answer 1

Hint
The coefficient of friction $\mu \;$ is a property of the surfaces in contact. It does not depend on any force acting on the surface nor the normal force.

Complete step by step answer
The coefficient of friction $\mu \;$ is a property of the surfaces in contact. It does not depend on any force acting on the surface nor the normal force. The coefficient of friction $\mu \;$ is a measurement of friction existing between two surfaces. A high value of coefficient of friction indicates that the force required for sliding to occur is more than the force required when the coefficient of friction is low. The formula for coefficient of friction is given by
$F = \mu \;N$ where,
$\mu \;$= coefficient of friction.
F = frictional force
N =normal force
Since the coefficient of friction $\mu \;$is a property of the surfaces in contact, therefore its values do not change on making the normal force 4 times.
Hence the correct answer is option (D) (remains the same).

Note
Coefficient of friction (COF) is a dimensionless number that is defined as the ratio between friction force and normal force. Materials with COF smaller than 0.1 are considered lubricous materials. COF depends on the nature of the materials and surface roughness.