In the S.I. system, identify the physical quantity that uses m^2/s as its unit.

Introduction / Context:
Recognizing units is a powerful shortcut in engineering exams. The unit m^2/s commonly appears in fluid mechanics when describing how momentum diffuses through a fluid, a property central to laminar versus turbulent behavior and to boundary-layer growth on surfaces.

Given Data / Assumptions:

• Kinematic viscosity is denoted by nu and defined as dynamic viscosity mu divided by density rho.
• Dynamic viscosity mu in S.I. is Pa·s (or N·s/m^2), and density rho is kg/m^3.
• Other listed quantities have different standard S.I. units (e.g., pressure → N/m^2).

Concept / Approach:
Kinematic viscosity nu = mu / rho characterizes diffusivity of momentum. It determines Reynolds number Re = V * L / nu, which separates flow regimes and strongly influences drag, head loss, and heat/mass transfer coefficients. Because it is a ratio of viscosity to density, its S.I. unit simplifies to m^2/s, highlighting its “diffusivity-like” nature similar to thermal diffusivity (alpha) with units m^2/s.

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