Question

An ideal fluid is:
A. Similar to a perfect gas
B. Non-viscous and incompressible
C. One which satisfies the continuity equation
D. One which obeys Newton’s formula for viscous drag.

Answer 1

Hint: Ideal fluid does not exist. There is always going to be some properties which will not be satisfied by the real fluids.

Complete step by step answer:

At first, let us look at the definition of fluid -

“Fluid is a gas or liquid that, unlike a solid, flows to assume the shape of the container in which it is placed.”

Hence, a fluid is basically which can flow and take the shape of any container. There are various properties of a fluid that defines the behaviour accurately. One of the most significant properties of liquid is viscosity. Based on the viscosity, there can be mainly 5 classes of fluids. The classification is as follows:

Ideal Fluid
Real Fluid
Newtonian Fluid
Non-Newtonian Fluid
Ideal Plastic Fluid.
Hence, we know that ideal fluid is there to derive a simple equation for the fluid flow. Ideal fluids have the following properties -

The density of the liquid stays constant (Incompressible)
There won’t be any turbulence (Irrotational)
There shouldn’t be any internal friction (Nonviscous)

However, no fluid can be considered to be ideal.

In this question, we will approach the options one by one and determine the answer.

A. The fluid is not similar to perfect gas, as perfect gas can be compressed indefinitely. However, the ideal fluid is incompressible.
B. This option fits the definition of an ideal fluid.
C. Real fluids also follow the continuity equation.
D. Newtonian fluids also follow the Newtonian equations.

Hence the correct option is (B).

Note: In our study, we only consider the fluids to be ideal because of simplicity. Ideal fluids follow continuity equations and Newtonian equations. The incompressible property is the reason behind Pascal’s rule.
You should approach this problem by figuring out which options are incorrect. For example, we could deem the option (C) to be wrong because both ideal and real fluids follow the continuity equation. Same goes for option (D).