**Fluid is categorized into four parts:**

**1. **Ideal Fluid

**2. **Real Fluid

**3. **Newtonian Fluid

**4.** Non-Newtonian Fluid

**1. Ideal Fluid:**

##### A fluid which is non-viscous & incompressible is known as ideal fluid. It is an imaginalry fluid i.e. No fluid is ideal fluid.

**2. Real Fluid:**

##### A fluid which posses viscosity is known as real fluid. All the fluis in actual oractice are real fluid.

e.g. water petrol etc.

**3. Newtonian Fluid:**

##### A fluid is said to be newtonian fluid if shear stress is directly proportional to rate of shear strain or angular deformation or velocity gradient.

In other words fluid which follow newton’s law of viscosity are known as newtonian fluid.E.g. Air, water, petrol, diesel, mercury, kerosine etc.

Newton’s law of viscosity is similar to hook’s law for solid.

**4. Non-Newtonian Fluid:**

A fluid which does not follow newtonian’s law of viscosity is known as non newtonian flid. Study of non-newtonian fluid is also known as rheology.

**The general relationship between shear stress (τ) and velocity gradient (du/dy) is: **

where A, n, B are constants

**CASE 1.**

**Dilatant fluid:** A fluid is said to be dilatant fluid id it’s apparent viscosity increases with the rate of deformation these fluids is also known as shear thickening fluid.

e.g. rice starch, sugar in water etc.

Here **B = 0 , n > 1 **

**CASE 2.**

**Pseudoplastic fluid:** A fluid is said to be a pseudoplastic fluid if the apparent viscosity decreases with rate of deformation these fluid is also known as shear thinning fluid.

e.g. blood, milk, colloidal solution etc.

Here **B = 0, n < 1**

**CASE 3.**

**Bingham plastic:** A fluid is said to be a bingham plastic if the apparent viscosity remains constant with rate of deformation these fluid.

e.g. toothpaste, hair gel etc.

Here B ≠ 0, n = 1