Question

The viscous force between two layers of a liquid is given by $\dfrac{F}{A} = \eta \dfrac{{dv}}{{dz}}$:
A. Pressure
B. Longitudinal stress
C. Tangential stress
D. Volume stress

Answer 1

A shear force will always act tangential to the plain of the fluid.

Complete step by step solution:
According to Newton’s law of viscosity,
$\tau = \dfrac{F}{A} = - \eta \dfrac{{dv}}{{dz}}$

As we know that viscous force acts like friction between the layer of two fluids due to which shearing action will occur, a shear force will always act tangential to the plane of the fluid/object. So, tangential stress will be generated between the two layers of the two fluids.

So, the correct option is option (c) i.e. Tangential stress

Additional information:
The tangential stress also known as hoop stress, is the stress around the circumference of the pipe due to a pressure gradient. The maximum hoop stress always occurs at the inner radius or the outer radius depending on the direction of the pressure gradient. Like the radial stress, the hope can be analyzed at any investigation point within the pipe wall at radius r. Therefore, tangential force is a force acting in generally a horizontal direction i.e. a force that produces folding and over thrusting.

Note: Students before being able to solve the sum students need to be able to understand the meaning of tangential and viscous force. Newton’s law of viscosity is a constitutive equation that describes how a fluid resists attempts to move through it. It holds true with some liquids and falls in others. Therefore, it is not considered a fundamental law of nature.