Stoke is the unit of:
Try it first: pick an option, then read the explanation.
Correct answer: B. Kinematic viscosity
Asked in SSC JE 2015
Detailed Explanation
The stoke is a widely recognized non-SI unit utilized across fluid mechanics and lubrication engineering.
Why “Kinematic viscosity” Is Correct
The stoke is defined as 1 cm²/s, which is the CGS unit of kinematic viscosity (\(\nu = \mu / \rho\)).
| Quantity | SI unit | CGS unit | Conversion |
|---|---|---|---|
| Dynamic viscosity μ | Pa·s (N·s/m²) | Poise (P) = dyne·s/cm² | 1 P = 0.1 Pa·s |
| Kinematic viscosity ν = μ/ρ | m²/s | Stoke (St) = cm²/s | 1 St = 10⁻⁴ m²/s |
| Surface tension T | N/m | dyne/cm | 1 dyne/cm = 10⁻³ N/m |
Why the Other Options Are Wrong
- A. Dynamic viscosity: Dynamic viscosity is measured in poise in CGS and Pa·s in SI.
- C. Specific volume: Specific volume is measured in m³/kg or cm³/g.
- D. Specific weight: Specific weight is measured in N/m³ or dyne/cm³.
Key Point
Stoke = 1 cm²/s = 10⁻⁴ m²/s; unit of kinematic viscosity.
Key Concepts for Students
- Named after Sir George Gabriel Stokes (1819–1903).
- Kinematic viscosity represents momentum diffusivity.
- 1 centistoke (cSt) = 1 mm²/s = 10⁻⁶ m²/s.
Practice more: this is question 54 in Properties of Fluid MCQs – Part 4. Try the whole set and check every answer instantly.