We were discussing the various basic concepts of
strength of materials and also the basic concepts of thermal engineering in our
previous posts. After looking strength of materials and thermal engineering
topics, we will go ahead to start a new subject i.e. Fluid mechanics with the
help of this post.

Before going ahead, we must have to find the post
indicating the basic definition and significance of fluid mechanics.

Now we will understand here the various properties
of fluid with the help of this post.

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Density
or Mass density

Density or mass density is basically defined as the
ratio of mass of fluid to the volume of fluid. Density of fluid will be
displayed by the symbol ρ.

We can write the basic formula for mass density as
mentioned here.

Density of fluid = Mass of fluid /Volume of fluid

ρ = m /v

####
**Unit
of density**

Unit of density will be Kg/m

^{3}in S.I system.
Density of gas changes according to pressure, but
density of liquid may be considered as unchangeable in general.

Water is considered as the standard liquid and
therefore we usually take water as reference liquid. Density of water at 4

^{0}C and 1 atm pressure is 1000 Kg/m^{3}.###
**Weight
density or specific weight**

Weight density or specific weight is basically
defined as the ratio of weight of fluid to the volume of fluid. Weight density
will be displayed by symbol w.

We can write the basic formula for weight density as
mentioned here.

Weight density of fluid = Weight of fluid /Volume of
fluid

w = W /v

w = m. g /v

w = ρ. g

Weight density of fluid = Mass density of fluid x
Acceleration due to gravity

####
*Unit
of weight density*

*Unit of weight density*

Unit of weight density of fluid will be N/m

^{3}
As stated above, water is considered as the standard
liquid and therefore we usually take water as reference liquid. Specific weight
or weight density of water at 4

^{0}C and 1 atm pressure is 9810 N/m^{3}.###
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Specific
volume

Specific volume is basically defined as the ratio of
volume of fluid to the mass of fluid. Specific volume will be displayed by
symbol v.

We can write the basic formula for specific volume
as mentioned here.

Specific volume = Volume of fluid /Mass of fluid

v = V /m

Specific volume = 1/Density

Therefore, we can also say that specific volume
could be defined as the reciprocal of mass density of the fluid.

####
*Unit
of specific volume *

*Unit of specific volume*

Unit of specific volume will be m

^{3}/Kg###
**Specific
Gravity**

Specific gravity is basically defined as the ratio
of mass density of liquid to the mass density of standard liquid. We already
stated above that water will be considered as standard liquid.

Therefore, we will again specify the specific
gravity as the ratio of mass density of liquid to the mass density of water.

Specific gravity = Mass density of liquid / Mass
density of water

Specific gravity = Weight density of liquid / Weight
density of water

Specific gravity will be displayed by symbol s.
Specific gravity is basically one ratio of mass density of given liquid to the
mass density of water and therefore specific gravity will be unit less.

We will discuss the term Viscosity of fluid in our
next post.

Do you have suggestions? Please write in comment
box.

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**Reference:**

Fluid mechanics by Y. Nakayama and R F Boucher

Image Courtesy: Google