Difficulty: Easy
Correct Answer: Poise
Explanation:
Introduction / Context:Viscosity units vary with unit systems. Converting and recognizing units correctly is essential when reading material property tables or correlating experimental data across metric and CGS literature.
Given Data / Assumptions:
Concept / Approach:
In CGS, the unit of dynamic viscosity is the poise (P). One poise equals 1 g/(cm·s), and 1 P = 0.1 Pa·s in SI. Kinematic viscosity in CGS uses stokes (St), where 1 St = 1 cm^2/s.
Step-by-Step Solution:
Recall: shear stress τ = μ * (du/dy). In CGS, τ in dyn/cm^2, gradient in s^−1 ⇒ μ unit dyn·s/cm^2 = g/(cm·s) = 1 poise.Relation to SI: 1 Pa·s = 10 P ⇒ 1 P = 0.1 Pa·s.Verification / Alternative check:
Typical dynamic viscosity of water at 20°C is about 1 cP (centipoise) = 0.001 Pa·s, matching the conversion above.
Why Other Options Are Wrong:
Dyne and Newton are force units; joule is energy; “none” is unnecessary because poise is the standard CGS unit.
Common Pitfalls:
Confusing centipoise (cP) with poise (P); many data sheets list viscosity in cP, where 1 cP = 0.01 P.
Final Answer:
Poise
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