Question

The ratio of inertial force to viscous force represents
A. Magnus effect
B. Reynolds number
C. Torricelli’s law
D. Relative density

Answer 1

Hint: We know that inertial force is a pseudo force which describes the motion of a body in the non-inertial frame. Here the reference is also in motion with respect to the body. Also, viscous force is the force which opposes the movement of a body in the fluid.

Complete step-by-step answer:
Let us consider the movement of a metal ball which is dropped in a vertical column containing some fluid, say water. Then when the ball tries to move in the water it experiences an opposing force called the viscous force. Also the water around the ball is also in motion with respect to the ball.
Then the ratio between the inertial forces to viscous force is called the Reynolds number.
The Reynolds number gives a better understanding of the fluid dynamics and is used to understand the turbulence or disturbance in the fluid when an object tries to move through it.

So, the correct answer is “Option B”.

Additional Information:
This concept was introduced by George Stokes, who gave the stokes law which describes the force experienced by an object in fluids, like air or water. He gave the Reynolds number to describe the frictional force or the drag force of the fluids. However, later another scientist Osborne Reynolds used the Reynolds number popularly to study the fluid dynamics. And is thus named after him.

Note: Clearly, the viscous force can also be called the fluid friction, as it resists the motion of the body in a fluid. It was observed that more the viscosity of the medium less is the Reynolds number. Which is to say that, if the medium is denser than the movement of the body in that fluid is slower.