Under what condition is the normal fluid stress identical in every direction at a point_______________?
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Answer: C. when there is no motion of one fluid layer relative to an adjacent layer
Explanation
When there is no relative motion between adjacent fluid layers, shear stresses are absent entirely. The absence of shear stress causes normal fluid stress to become isotropic, remaining equal in every direction at a point. This fundamental condition applies to stationary fluids and frictionless fluid flows lacking velocity gradients. Fluid statics and dynamics analyze stress tensors to determine pressure distributions within liquid and gas systems. Pascal's law states that pressure applied to an enclosed fluid is transmitted undiminished in every direction. Viscosity generates internal shear stresses only when adjacent fluid layers slide past each other at different velocities.
Hydraulic press designs rely on isotropic pressure transmission principles to multiply mechanical forces efficiently. Fluid mechanics engineers use hydrostatic equations to calculate pressure forces acting on submerged engineering structures. Assuming zero relative layer motion simplifies complex fluid pressure calculations in closed hydraulic systems. Option A specifies frictionless fluids, but lack of relative motion is the precise operational condition required. Option B unnecessarily restricts the condition to incompressible fluids with zero viscosity. Option D is incorrect because relative motion introduces shear stresses that alter stress uniformity across directions.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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