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 Reynolds Number Definition.
The Reynolds number is defined as: \[Re = \frac{\rho V L}{\mu} = \frac{\text{Inertia force}}{\text{Viscous force}}.\]

Step 2: Evaluate Options.
- (1) Viscous/Inertia: Incorrect, this is the inverse of the Reynolds number.
- (2) Elastic/Pressure: This ratio is associated with the Mach number, not the Reynolds number.
- (3) Inertia/Viscous: Correct, this matches the definition.
- (4) Gravity/Inertia: This ratio is associated with the Froude number, not the Reynolds number.

Step 3: Finalize Conclusion.
Therefore, the Reynolds number represents the ratio of inertia force to viscous force.