VISCOSITY

VISCOSITY

        Viscosity is defined as the property of a fluid which offers resistance to the movement of one layer of fluid over another adjacent layer of the fluid. When two layers of a fluid, a distance ‘dy’ apart, move one over  the other at different velocities, say  ‘u’ and  ‘u + du’ as shown in below figure, the velocity together with relative velocity causes a shear stress acting between the fluid layers. 

         The top layer causes a shear stress on the adjacent lower layer while the lower layer causes a shear stress on the adjacent top layer. This shear stress is proportional to  ‘y’ . It is denoted by symbol ‘tau’.

   

  Units of Viscosity 

          

    MKS unit of viscosity = kgf -sec/m²

     CGS unit of  viscosity = dyne -sec/cm²

      SI unit of viscosity = Newton - sec/ m²

    

                  The unit of viscosity in CGS is also called Poise which is equal to  dyne -sec/cm².

                Note - 

                          1. If viscosity is given in poise, it must be divided by 10 to get its equivalent numerical value in SI units. 

            The viscosity of water at 20°C is 0.01 poise or 1.0 centipoise. 

KINEMATIC VISCOSITY 

                          It is defined as the ratio between the dynamic viscosity and density of fluid. It is denoted by the Greek symbol called ‘nu’.

UNITS OF KINEMATIC VISCOSITY

                                 In MKS and SI, the unit of kinematic viscosity is ‘metre²/sec’ while in CGS units it is written as ‘cm²/sec’. In CGS units, kinematic viscosity is also known as ‘stoke’.

                                            The End. 

    Please comment if you have any query. 

Disclaimer : An attempt has been made to make this blog error free. If there is any error, please forgive.

       



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