Question

According to Stoke's law, velocity of fat globule rise is inversely proportional to ____________

• A. Gravitational force
• B. Diameter of fat globule
• C. Viscosity of plasma
• D. Density of fat globule

Hint:

According to Stokes' Law, higher milk plasma viscosity slows down fat separation. This is why homogenization (which indirectly increases viscosity and reduces fat globule size) prevents creaming.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Stokes' Law defines the terminal velocity of spherical particles (such as fat globules) moving through a viscous fluid medium (such as milk plasma) under the influence of gravity.
Key Formula or Approach:
The velocity of rise (\(v\)) of a fat globule is expressed by the equation:
\[ v = \frac{2 \cdot g \cdot (\rho_p - \rho_f) \cdot r^2}{9 \cdot \eta} \]
where:
- \(g\) is the acceleration due to gravity,
- \(\rho_p\) is the density of the plasma (skim milk),
- \(\rho_f\) is the density of the fat globule,
- \(r\) is the radius of the fat globule, and
- \(\eta\) is the dynamic viscosity of the plasma.

Step 2: Detailed Explanation:
From the formula:
- Velocity (\(v\)) is directly proportional to the square of the globule radius (or diameter).
- Velocity is directly proportional to the density difference (\(\rho_p - \rho_f\)) and gravitational force (\(g\)).
- Velocity is located in the numerator while the dynamic viscosity of the plasma (\(\eta\)) is in the denominator.
- This mathematically demonstrates that the rate of creaming (velocity of rise) is inversely proportional to the viscosity of the plasma.

Step 3: Final Answer
The velocity of fat globule rise is inversely proportional to the viscosity of the plasma.