Identify which fluid property in the S.I. system uses N·s/m^2 (Pa·s) as its unit.

Introduction / Context:
Viscosity quantifies a fluid’s resistance to deformation. Two related but distinct properties appear in problems: dynamic viscosity (mu) and kinematic viscosity (nu). Distinguishing their units avoids errors in Reynolds number, head-loss predictions, and pump sizing calculations.

Given Data / Assumptions:

• Dynamic viscosity mu relates shear stress to velocity gradient in Newtonian fluids: tau = mu * du/dy.
• Kinematic viscosity nu = mu / rho.
• Density rho is kg/m^3; specific weight gamma is N/m^3.

Concept / Approach:
From tau = mu * (du/dy), shear stress tau has units N/m^2 and du/dy has units 1/s. Therefore mu must have units (N/m^2) / (1/s) = N·s/m^2. The same unit is called pascal-second (Pa·s). Kinematic viscosity is a ratio of mu to rho and carries m^2/s, not N·s/m^2.

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