Question

Kinematic viscosity can be defined as

• A. Ratio of dynamic viscosity to density
• B. Ratio of pressure to density
• C. Product of dynamic viscosity and density
• D. Product of pressure and density

Hint:

To remember the definition of kinematic viscosity, look at its units: $\nu = \mu / \rho$. It represents the ratio of dynamic viscosity (force/area $\times$ time) to density (mass/volume).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Viscosity is a physical property of fluids that measures their resistance to gradual deformation by shear or tensile stress.
There are two ways to express viscosity: dynamic (absolute) viscosity and kinematic viscosity.
Kinematic viscosity measures a fluid's resistance to flow under the influence of gravity, which depends on both the fluid's molecular friction and its density.
Key Formula or Approach:
The mathematical definition of kinematic viscosity ($\nu$) is:
\[ \nu = \frac{\mu}{\rho} \]
Where:
$\mu$ is the dynamic viscosity (in Pa$\cdot$s or kg/m$\cdot$s).
$\rho$ is the fluid density (in kg/m$^3$).

Step 2: Detailed Explanation:
Dynamic viscosity ($\mu$) represents the internal friction between fluid layers.
However, when a fluid flows under gravity, its inertia (density, $\rho$) resists this motion.
Kinematic viscosity ($\nu$) combines these two effects, representing the rate at which momentum diffuses through the fluid.
The SI unit for kinematic viscosity is m$^2$/s, although it is often expressed in stokes (St) or centistokes (cSt), where:
\[ 1 \text{ cSt} = 10^{-6} \text{ m}^2/\text{s} \]
This property is critical for designing piping systems, pumps, and liquid transport lines in dairy processing plants.
Therefore, kinematic viscosity is defined as the ratio of dynamic viscosity to density.

Step 3: Final Answer
Kinematic viscosity is defined as the ratio of dynamic viscosity to density.