Falling Sphere Viscometer (Stoke’s Law Viscometer)

• Falling Sphere Viscometer (Stoke’s Law Viscometer) is used in labs for accurate fluid viscosity analysis.
• Falling Sphere Viscometer (Stoke’s Law Viscometer) measures viscosity by tracking a sphere’s fall through liquid.

Principle:

• A ball (usually steel or glass) falls through the test liquid under gravity.
• The terminal velocity of the ball is used to calculate viscosity, using Stoke’s law:
• $\eta = \frac{2 r^{2} \, (\rho_{s} – \rho_{l}) \, g}{9 v}$
• Where:
  • r: radius of the sphere
  • ρ_s​: density of the sphere
  • ρ_l​: density of the liquid
  • g: gravitational acceleration
  • v: terminal velocity

Apparatus:

• Hoppler viscometer

Application:

• Used for Newtonian fluids and some low-shear non-Newtonian fluids.
• Suitable for transparent fluids (so you can observe the falling ball).

Advantages:

• Simple concept
• Useful for viscous Newtonian liquids (e.g., oils)

Limitations:

• Limited to transparent fluids
• Cannot measure thixotropy or other complex behaviors

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