Fundamentals Of Fluid Mechanics: 9 Important Concepts

What is fluid mechanics?

The fluid mechanics can be elaborated as the study of fluid and fluid systems for their physical behaviour, governing laws, actions of different energies and different flow pattern.

The fluid is sub-divided into two types :

  1. Liquid
  2. Gas

The fluid mechanics is the subject of engineering which will be useful in many engineering discipline. The subject of fluid mechanic is important in mechanical engineering, civil engineering, chemical engineering and environment engineering etc.

Even the study of geology, geophysics, ocean and nano science also requires some knowledge of fluid mechanics and fluid dynamics.

It is interesting for you that some basic laws of fluid mechanics is involved in primary and secondary education, so it can be expected that it is familiar subject for you.

What are the fluid mechanics branches?

There are three branches of fluid mechanics based on forces and energy.


The hydrostatics can be defined as fluid mechanics studying when the fluid or fluid element at rest. It means there is no fluid flow. There are no shearing stresses.

We can take an example of fluid at rest like a dam, pond etc.

Fluid Mechanics : Hydro static structure dam
Hydro static structure dam

The dam is very known example of hydrostatic branch. In holidays you might have visited some famous dam near you.


The kinematics is the study of fluid mechanics about fluid motions like translation, rotary or deformation. Remember-> There is no consideration of forces and energy acting on fluid (Fluid in motion) in this study.

Here, the fluid is flowing so we can take example of flowing fluid in river, canal etc.


The fluid dynamics is a complete study of flowing fluid. It studies velocity, acceleration, forces and energies acts on the fluid in motion.

Here, the study of flowing fluid (Fluid in motion) is carried out by considering forces and energy acts on it. The example of fluid dynamic are fuel flow inside diesel fuel injector, liquid flow inside pump, fluid flow inside turbine etc.

Fluid flow | What is fluid flow?

When gas or liquid is travelling or moving fluid from one point (destination) to another point, we can call it fluid flow.

Let’s understand in another word, the trend of continuous deformation of fluid is known as fluidity. The action of this continuous deformation is known as fluid flow.

For example flow of wind, flow in the river, waves in the sea, liquid flow in pipelines etc.

Classification of fluid

In common term, there are two types of fluid as given below,

  1. Ideal fluid
  2. Real fluid

What is the ideal fluid?

First, keep it in mind “there is no existence of ideal fluid in nature and it is imaginary fluid”. In practical purpose, we are considering water and air as an ideal fluid for many studies because of its lower viscosity.

The water is incompressible, so it is closer to an ideal fluid as compared to air.

Ideal fluid possess the following characteristics,

  • Incompressible
  • Non-viscous (Inviscid)
  • No friction (Frictionless)
  • No surface tension

The ideal fluid possesses no viscosity. It means that the friction does not exist in the fluid. The ideal fluid is our imagination of standard fluid with superior characteristics. In nature, there is always frictional resistance whenever any motion exists.

What is real fluid?

The all fluid in nature can be considered as real. Let’s see why?

It possesses most of the practical characteristics,

  • Viscous
  • Compressible
  • Friction
  • Surface tension

Principles of fluid dynamics

Some of the basics principles of fluid dynamics are enlisted below for your information. The study of each principle in detail with our next articles will take you in-depth of fluid dynamics.

  • Conservation of mass, momentum and energy
  • Newton’s law of viscosity
  • Principles of continuity
  • Momentum equation and energy
  • Euler’s equation
  • Bernoulli’s theorem
  • Archimede’s principle
  • Pascal’s law
  • Laws of similarities and model
  • Rayleigh’s method and Buckingham pi-theorem
  • Navier stock equation
  • Reynold and Darcy equation

These principles are helpful since many of the approaches and techniques of analysis used in fluid mechanics problems. It will be well understood when you come across real problems on fluid mechanics.

Fluid Mechanic applications

The fluid mechanics subject encircles numerous applications in domestic as well as industrial. Some of the applications are enlisted below,

  • The water distribution channel network and pipelines in domestic and industrial.
  • The hydraulics machinery and hydraulic structures are designed based on fluid mechanics.  Hydraulics Machinery: Turbines, pumps, valves, fluid couplings, actuators etc.
Cross sectional view of Centrifugal Pump [Image Credit]

Hydraulic structures: Canal, dams, weirs, overhead tanks etc.

  • The fundamental of fluid dynamics can be used to design supersonic aircraft, missiles, gas turbine, rocket engines, torpedo, submarine etc.
  • The power plants like hydroelectric power, thermal (steam) power, gas turbine power uses fluid mechanics.
Turbine [Image Credit. Power mag]
  • The fluid mechanics have vast applications in measurement devices of pressure, velocity and flow measurement instruments.

Pressure measurement: Bourdon tube pressure gauge, vacuum gauge, manometer etc.

Velocity and flow measuring instruments: Pitot tube, current meter, venturi meter, orifice meter, rotameter etc.

Venturimeter [Image Credit]
  • Some of the scientific subjects like oceanography, meteorology, geology etc. also require fluid dynamics.
  • The pneumatics and hydraulic various fluid control devices
  • Even if we consider blood flowing inside the human vein possess fluid dynamics

In nature, there are so many processes governed by fluid mechanics and fluid dynamics laws. Example: Rise of groundwater to top of the tree, rainwater cycle, wind flow and waves, ocean waves, weather patterns etc.

Let’s understand some practical applications of fluid dynamics, which will become very familiar with you.

You might have your automobile vehicle bike or car. You know that air is infiltrated inside vehicle tyres with pressure, so it possesses pressure laws.

Secondly, the shock absorber is filled with oil which absorbs jerk or shock. The oil will get pressurized and provide cushioning to your vehicle. There numerous day to day applications in your life that is totally or partially governed by fluid mechanics or dynamics.

Units and Dimensions

Since our subject is fluid mechanics, we will study a variety of fluid characteristics; it is a requirement to follow a system for indicating these attributes, both qualitatively and quantitatively.

The qualitative aspect describes to find the nature, or type, of the characteristics like length, time, stress, temperature, velocity and pressure on the next side the quantitative aspect indicates a value measure of the attributes.

A dimension can be defined as a description of measurable quantities or attributes of an object such as mass, length, temperature, pressure, time etc.

The understanding of unit can be considered as the standard for measuring the dimension or quality.

To understand the difference between units and dimensions, let’s take an example of the distance between Mumbai and Goa.

The term length is used to describe the qualitative concept of physical quantity.

The term unit indicates the magnitude of the distance between Mumbai and Goa in our example. This distance can be expressed in meter, kilometre or miles.

There are four fundamentals dimensions used in the physical dimensioning system. In the SI (standard international) system, the dimensions are mass, length, time and temperature. Let’s understand how it works?

International System (SI). In 1960, the 11th General Conference organised on Weights and Measures, the international organization responsible for managing precise, systematic standards of measurements, properly accepted the International System of Units as the international standard. This system, generally termed SI, has been broadly accepted worldwide and is broadly used.

Mass (M)Kilogramkg
Length (L)Meterm
Time (T)Seconds
Temperature (K)KelvinK

These are the fundamental units of the SI system. Other all the units of any physical properties can be derived based on these four units. Let’s take some example to understand it better way.


 You have heard about work. The unit of work is Joule. Now we expand its unit.

In other words, it is an energy transfer of any object when it moved from one place to another place. The force can be positive or negative.

Work = Force * Distance

The newton (N) is a unit of force, and the unit meter is a unit of distance. So the unit of work,

Unit of work = Newton* meter =N*m =Joule (J)


The formula of density is given as below.

Density = mass per unit volume

Here, the unit of mass is kg, the unit of volume is m3.

The unit of density is kg/m3

The density of water is considered 1000 or 997 kg/m3. The density of air is 1.225 kg/m3

Its means that water is considered standard dense and it is heavier than much other liquid. The air is significantly lighter, and it is a highly compressible fluid.


The definition of power is given as the ability of doing work in unit time. Or we can say work done per unit time.

Power = Work done per unit time.

The unit of work is Joule (J) and the unit of time is second (s).

The unit of power is derived as J/s (Joule/second). The unit Joule/second is in general known as watt (w).

Questions and Answers

What are types of fluid according to state?

According to the state, there are two types of fluid.

  1. Liquid
  2. Gas

Give the name of fluid mechanics branches.

  1. Hydrostatics
  2. Fluid kinematics
  3. Fluid dynamics

What is real fluid?

It possesses most of the practical characteristics,

  1. Viscous
  2. Compressible
  3. Friction
  4. Surface tension

Define: Dimension and unit

A dimension can be defined as a description of measurable quantities or attributes of an object such as mass, length, temperature, pressure, time etc.

The understanding of unit can be considered as the standard for measuring the dimension or quality.

Give four fundamental dimensions of SI (Standard International).

Mass (M)
Length (L)
Time (T)
Temperature (K)

What is SI (Standard International) System?

International System (SI). In 1960 the 11th General Conference organized on Weights and Measures, the international organization responsible for managing precise, systematic standards of measurements, properly accepted the International System of Units as the international standard.

Enlist three applications of fluid mechanics.

  • Design supersonic aircrafts
  • The water distribution channel network
  • The pneumatics and hydraulic various fluid control devices

What are the pressure measuring instruments?

  • Bourdon tube pressure gauge
  • Vacuum gauge
  • Manometer

Give any three names of fluid mechanic principles.

  • Bernoulli’s theorem
  • Rayleigh’s method and Buckingham pi-theorem
  • Archimede’s principle

MCQ on Articles

Choose the fluid mechanics branch; the study includes force and energy acts on moving fluid?

(a) Hydro statics               (b) Fluid kinematics         (c) Fluid dynamics            (d) None

In which of the following fluid mechanics branch, there is no shearing stress or fluid motion?

(a) Hydro statics               (b) Fluid kinematics         (c) Fluid dynamics            (d) None

An ideal fluid is known as the fluid which is________

(a) In-compressible          (b) Compressible             (c) Viscous          (d) None

A real fluid is one which possesses ________

(a) In-compressible          (b) Viscous             (c) Inviscid           (d) Frictionless

Which of the following is basic principle of fluid dynamics?

(a) Newton’s law of cooling         (b) Newton’s law of viscosity

(c) Law of gearing                            (d) Stefan-Boltzmann

Which of the following is the hydraulic machinery?

(a) Spiral gear    (b) Crank shaft  (c) Turbine          (d) drilling

Choose the name of hydraulic structure from the following choices.

(a) house beam                (b) Machine structure     (c) Dam (d) None

Which of the following is a flow measurement device?

(a) Rotameter   (b) Bourdon tube gauge (c) Manometer               (d) None

What is the unit of Power?

(a) J/s    (b) J       (c) Nm  (d) K

What is the unit of the density?

(a) kg      (b) m/s (c) kg/m3 (d) m2


This article is helpful to get the basic knowledge about fluid mechanics fundamental. The article includes an understanding of some basics terms like hydrostatics, fluid kinematics and fluid dynamics. The list of various fluid mechanics principle and applications are provided to get an idea about subject and future learning topics. In last, the dimension and unit definitions are given with detailed examples.

This article teaches you to visualize and remember applications of fluid mechanics in your day to day life. You have to collaborate with applications with fluid mechanic’s principles.

More topic related to fluid mechanics, please click here.

Deepakkumar Jani

I am Deepak Kumar Jani, Pursuing PhD in Mechanical- Renewable energy. I have five years of teaching and two-year research experience. My subject area of interest are thermal engineering, automobile engineering, Mechanical measurement, Engineering Drawing, Fluid mechanics etc. I have filed a patent on "Hybridization of green energy for power production". I have published 17 research papers and two books. I am glad to be part of Lambdageeks and would like to present some of my expertise in a simplistic way with the readers. Apart from academics and research, I like wandering in nature, capturing nature and creating awareness about nature among people. Let's connect through LinkedIn - Also refer my You-tube Channel regarding “Invitation from Nature”

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