**Newton's law of viscosity** gives the viscous force as $F = \eta A (dv/dx)$ where $dv/dx$ is the **velocity gradient**. The SI unit of coefficient of viscosity $\eta$ is:
AN·s/m²
BN/m²
Ckg/m
Dm²/s
Answer & Solution
Correct answer: A. N·s/m²
From $F = \eta A (dv/dx)$: units of $\eta$ = N / (m² × s⁻¹) = N·s/m² = Pa·s. CGS unit: poise (1 Pa·s = 10 poise).
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