Question

Reynolds number is defined as the ratio of:

• A. Viscous force to Inertia force
• B. Elastic force to Pressure force
• C. Inertia force to Viscous force
• D. Gravity force to Inertia force

Hint:

Reynolds number distinguishes laminar and turbulent flow: $Re < 2000$ (laminar), $Re > 4000$ (turbulent).

Answer 1

The Correct Option is C

Step 1: Recall definition of Reynolds number.
Reynolds number is: \[ Re = \frac{\rho V L}{\mu} = \frac{\text{Inertia force}}{\text{Viscous force}}. \]

Step 2: Check options.
- (1) Viscous/Inertia = Wrong (inverse of Reynolds).
- (2) Elastic/Pressure = Related to Mach number, not Reynolds.
- (3) Inertia/Viscous = Correct definition.
- (4) Gravity/Inertia = Related to Froude number, not Reynolds.

Step 3: Conclusion.
Hence, Reynolds number is the ratio of inertia force to viscous force.