Flow of fluid take place due to its:
Try it first: pick an option, then read the explanation.
Correct answer: D. Deformation under shear force
Asked in SSC JE 2010
Detailed Explanation
The fundamental distinction between a solid and a fluid lies in their response to shear stress. Solids deform until static equilibrium is reached, whereas fluids deform continuously as long as the shear force acts.
Why “Deformation under shear force” Is Correct
Flow occurs because fluids cannot sustain static shear stresses; any applied shear force produces continuous, progressive angular deformation (flow).
Why the Other Options Are Wrong
- A. Viscosity: Viscosity opposes flow rather than causing it.
- B. Compressibility: Compressibility describes volume change under normal pressure, not shear flow.
- C. Surface tension: Surface tension tends to minimize surface area and contract fluids, not initiate flow.
Key Point
Fluid flow is the continuous deformation of fluid elements under applied shear force.
Key Concepts for Students
- A fluid cannot remain at rest under a shear stress.
- Shear rate du/dy continues as long as shear stress τ is applied.
- Solids resist shear by finite strain; fluids resist shear by strain rate.
Practice more: this is question 67 in Properties of Fluid MCQs – Part 5. Try the whole set and check every answer instantly.