# Basic Concepts | Fluid Mechanics – Interview Question and Answers

In this post we will see Basic Concepts of Fluid mechanics interview questions with answers. These Questions are useful for interviews, viva , Oral Examination , Objective type technical Questions.

** 1. Define density or mass density.**

Density of a fluid is defined as the ratio of the mass of a fluid to its volume.

**Density, ρ = mass/volume (Kg/m3)**

ρwater = 1000 Kg/m3

**2. Define specific weight or weight density.**

Specific weight or weight density of a fluid is defined as the ratio between the weight of a fluid to its volume.

**Specific weight, γ = weight/volume (N/m3 )**

γ = ρg

γwater = 9810 N/m3

**3. Define specific volume.**

Specific volume of a fluid is defined as the volume of fluid occupied by an unit wt or unit mass of a fluid.

**Specific volume vs = volume/ wt = 1/γ = 1/ρg —– for liquids**

**Specific volume vs = volume/ mass = 1/ρ —– for gases**

**4. Define Kinematic viscosity.**

It is defined as the ratio between the dynamic viscosity and density of fluid.

ν = μ/ρ (m2 /s)

**5. Types of fluids.**

Ideal fluid, Real fluid, Newtonian fluid, Non-Newtonian fluid, Ideal Plastic fluid.

**6. Define Surface Tension.**

Surface tension is defined as the tensile force acting on the surface of the liquid in contact with a gas or on the surface between two immiscible liquids such that the contact surface behaves like a membrane under tension.

**Surface Tension, σ = Force/Length (N/m)**

**7. Define Vapour Pressure.**

When vaporization takes place, the molecules start accumulating over the free liquid surface exerting pressure on the liquid surface. This pressure is known as Vapour pressure of the liquid.

**8. List the types of fluid flow.**

Steady and unsteady flow

Uniform and non-uniform flow

Laminar and Turbulent flow

Compressible and incompressible flow

Rotational and ir-rotational flow

One, Two and Three dimensional flow

**Read in Details :**Types of Flows in a Pipe /Fluid Mechanics

**9. Define Compressible and incompressible flow**

**Compressible flow**

The compressible flow is that type of flow in which the density of the fluid changes from point to point i.e. the density is not constant for the fluid. It is expressed in kg/sec.

ρ ≠ constant

**Incompressible flow**

The incompressible flow is that type of flow in which the density is constant for the fluid flow. Liquids are generally incompressible. It is expressed in m3 /s.

ρ = constant

**10. State the assumptions used in deriving Bernoulli’s equation**

- Flow is steady;
- Flow is laminar;
- Flow is irrotational;
- Flow is incompressible;
- Fluid is ideal.

**Read More : Introduction to Bernoulli’s equation and It -Application**

**11. Define dimensional analysis.**

Dimensional analysis is a mathematical technique which makes use of the study of dimensions as an aid to solution of several engineering problems. It plays an important role in research work.

**12. . Define model and prototype.**

The small scale replica of an actual structure or the machine is known as its Model, while the actual structure or machine is called as its Prototype. Mostly models are much smaller than the corresponding prototype.

**13. Mention the various forces considered in fluid flow.**

Inertia force, Viscous force, Gravity force,

Pressure force, Surface Tension force, Elasticity force

**14. State Euler’s model law**

In a fluid system where supplied pressures are the controlling forces in addition to inertia forces and other forces are either entirely absent or in-significant the Euler’s number for both the model and prototype which known as Euler Model Law.

**15. What are fluid machines or Hydraulic machines?**

The machines which use the liquid or gas for the transfer of energy from fluid to rotor or from rotor to fluid are known as fluid machines.