Question

Viscous force is somewhat like friction as it opposes, the motion and is non-conservative but not exactly so because
This question has multiple correct options
a) It is velocity dependent while friction is not
b) It is velocity independent while friction is not
c) It is temperature dependent while friction is not
d) It is independent of area like surface tension while friction is dependent.

Answer 1

Hint: The viscous force is the force that comes into action when a fluid is in motion and which opposes the relative motion between different layers. Now that we have discussed how the viscous force comes into picture we will see on what parameter it depends. Accordingly we will compare those will the force of friction and accordingly select the multiple correct answers from the question above.

Complete answer:
Viscous force comes into action when two layers of liquid pass each other travelling with different velocities. Newton’s formula for viscous force between two parallel layers is given by,
$F=\eta A\dfrac{dv}{dx}$ where A is the area of the two layers in contact with each other, $\eta $is the coefficient of viscosity and $\dfrac{dv}{dx}$ is the rate of change of velocity with distance(between the two layers) in the direction of increasing distance. Hence we can conclude from this that the viscous force between two layers depends on the velocity gradient of the two layers. It is also to be noted that the coefficient of viscosity decreases with temperature. This is because as the temperature increases the fluid becomes less dense and the molecules of the liquid become more free to move around. Speaking about the frictional force it only depends on the normal to the surface. It does not depend on the velocity of the body and neither changes with temperature.

So, the correct answer is “Option A and C”.

Note:
Though above we have discussed the points of dissimilarities, let's discuss some of the similarities between viscous force and the force due to friction. Both the forces come into play when there is relative motion. Both oppose the motion and are a result of molecular attractions.