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In a Newtonian fluid, the viscous stress is proportional to:
A{'text': 'Strain (NOT strain rate)', 'label': 'A'}
B{'text': 'STRAIN RATE: $\\sigma_{ij}^d = \\mu (\\partial u_i/\\partial x_j + \\partial u_j/\\partial x_i)$, where μ is dynamic viscosity', 'label': 'B'}
C{'text': 'Pressure', 'label': 'C'}
D{'text': 'Temperature gradient', 'label': 'D'}
Answer & Solution
Correct answer: B. {'text': 'STRAIN RATE: $\\sigma_{ij}^d = \\mu (\\partial u_i/\\partial x_j + \\partial u_j/\\partial x_i)$, where μ is dynamic viscosity', 'label': 'B'}
Newtonian fluids: viscous stress ∝ strain rate (rate-of-deformation tensor). μ is the dynamic viscosity. This linear relation distinguishes Newtonian (water, air) from non-Newtonian fluids (Bingham plastics, shear-thinning polymers).
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