## Friday, 8 December 2017

Now we will understand here the Newton’s law of viscosity, in the subject of fluid mechanics, with the help of this post.

### 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