# What is fluid Viscocity, Units & Types of Fluid?

**What is fluid Viscocity? **

**Viscosity**** is the property of the fluid through which it offers resistance to the movement of one layer of fluid over the adjacent layer of the fluid.**

**Viscosity**** is the property of a fluid but it is manifested only when the fluid is in motion.**

**Viscosity**** property is nothing to do when the fluid is at rest.**

**When two layers comes in contact the upper layer of fluid which have a higher velocity try to drag the lower layer of the fluid in the direction of the fluid flow. Thus offers a force on the lower layer of fluid. According to Newton’s 3rd law the lower layer offers equal and opposite force in opposite direction of fluid flow.**

**Thus the velocity of different layer of fluid varies and shear stress comes into picture.**

**The formula for measuring viscosity is as:**

*viscosity = shear stress / shear rate *

**This equation is also known as Newton’s law of Viscocity.**

**Unit of Viscocity :**

**SI Unit : Nsec/m^2 or Pascal.sec**

**CGS Unit : dyne-sec/cm^2**

**The result is typically expressed in centipoise (cP), which is the equivalent of 1 mPa s (millipascal second). **

**Shear stress is the force per unit area required to move one layer of fluid in relation to another.**

**Shear rate is the measure of the change in speed at which intermediate layers move with respect to one another.**

**Newtonian vs. Non-Newtonian Fluids**

**Those fluid which obeys Newton’s law of Viscocity is termed as Newtonian Fluid. example : Water, Honey etc.**

**Those fluid which doestn’t obeys Newton’s law of Viscocity is termed as Non – Newtonian Fluid.example : blood, Milk, Polymer Solution etc.**

**Non Newtonian Fluid Further catogeroised into two main category i.e.**

**1)Time Independent**

**2) Time Dependent**

**These above mentioned two category further classified into : thixotropic, rheopectic, pseudoplastic, dilatant, and bingham-plastic. Different considerations are required when measuring each of these fluid types.**

ImageSource : Wikipedia

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