Question

What is Kinematic viscosity?

1. It is the ratio of dynamic viscosity to mass density.
2. it is the rate of change of shear stress.
3. It is the rate of change of shear strain.
4. It is the ratio of dynamic viscosity to relative density.

Answer 1

Correct Answer - Option 1 : It is the ratio of dynamic viscosity to mass density.

Explanation:

Viscosity:

Due to the presence of viscosity in the fluids, it offered the resistance to flow on the surface. There are two types of viscosity of fluids.

Dynamic viscosity (µ):

The Dynamic viscosity is also known as absolute viscosity. It is defined as the measurement of the fluid's internal resistance to flow

• SI units Ns/m² or kg/ms.
• CGS unit is poise (Dyne-s/cm²).
• 1 poise = 0.1 Ns/m².

Kinematic viscosity (ν):

The kinematic viscosity is an atmospheric variable defined as the ratio between the dynamic viscosity (μ) and the density (ρ) of the fluid and depends on both air temperature and pressure.

ν = \(\frac{Dynamic~viscosity~(\mu)}{Mass~ density~(\rho)}\)

• SI unit is m²/s.
• CGS unit is cm²/s or stoke.
• 1 stoke = 10^-4 m²/s = cm²/s.

• In liquid, the viscosity is due to the intermolecular force of cohesion.
• In gas, the viscosity is due to the transfer of molecular momentum between the layers of fluid.
• The viscosity of a gas increases with an increase in temperature whereas the viscosity of liquid decreases with an increase in temperature.
• The viscosity of water is 1 centipoise at 20°C.