Viscosity (Dynamic & kinematic)

◆ Viscosity ◆

▶️ Dynamic Viscosity= it is a definite as the property of a liquid which a fraction resistance is offered by a layer to the sliding of another layer over it.

● The resistance is due to cohesion and molecular momentum transfer between the fluid layers.

● Viscosity is a measure of internal fluid friction which causes resistance to the flow and hence controls the rate of flow.

τ = μ dc / dy 

 τ = μ γ 

 where 

τ = shearing stress in fluid (N/m²)

 μ = dynamic viscosity of fluid (N s/m²)

 dc = unit velocity (m/s)

 dy = unit distance between layers (m)

 γ = dc / dy = shear rate (s^-1)

● Unit of viscosity or dynamic viscosity.

=N-s/m^2 or Poise=0.1 N-s/m^2

▶️ Kinematic Viscosity= It is defined as the ratio of dynamic viscosity to the mass density.

ν = μ / ρ 

Where

   ν = kinematic viscosity (m²/s)

   μ = absolute or dynamic viscosity (N s/m²)

    ρ = density (kg/m³)

● Unit of kinematic viscosity

= M^2/s.........SI unit

=Stoke ..........CGS unit.

⛔Note:- Viscosity of fluid more, slower the motion of fluid.

for liquids - viscosity decreases with temperature.
for gases - viscosity increases with temperature.

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