We were discussing the basic definition and significance of Fluid mechanics, Kinematic viscosity, Dynamic viscosity, various properties of fluid and types of fluids in our previous post.

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**Newton’s
law of viscosity**

According to the Newton’s law of viscosity, shear
stress in a flowing fluid will be directly proportional to the rate of shear
strain.

We can also say that

Shear stress Î± Rate of shear strain

Ï„ Î± [du/dy]

Ï„ = Î¼ [du/dy]

Where, constant of proportionality will be termed as
viscosity of the fluid.

###
**Let us see the importance of Newton’s law of viscosity**

Fluids are classified in Newtonian fluids and Non-Newtonian
fluids on the basis of Newton’s law of viscosity.

###
**Newtonian
fluid**

Newtonian fluid is basically defined as a fluid in
which shear stress will be directly proportional with the velocity gradient.

We can also say that a fluid which follows the
Newton’s law of viscosity will be termed as Newtonian fluid.

*Example:*
Water, Air, Benzine etc

###
**Non-
Newtonian fluid**

Non- Newtonian fluid is basically defined as a fluid
in which shear stress will not be directly proportional with the rate of shear
strain or velocity gradient.

We can also say that a fluid which does not follow
the Newton’s law of viscosity will be termed as Non- Newtonian fluid.

*Example:*
Plaster, Flubber, Slurries and Pastes etc.

We will now discuss the concept of Compressibility and Bulk modulus in the category of fluid mechanics in our next post.

Do you have suggestions? Please write in comment
box.

###
**Reference:**

Fluid mechanics by Y. Nakayama and R F Boucher

Image Courtesy: Google