Choose the correct statement about fluid behavior and rheology:

Introduction / Context:
Rheology classifies fluids by the relationship between shear stress and rate of deformation. Correctly identifying Newtonian versus non-Newtonian behavior is essential in pipeline design, food processing, drilling muds, and biomedical flows.

Given Data / Assumptions:

• Shear flow between parallel plates (canonical reference).
• Steady shear; temperature constant.
• “Plastic” refers to materials exhibiting a yield stress (e.g., Bingham or Herschel–Bulkley types).

Concept / Approach:

Newtonian fluids obey τ = μ * (du/dy) where μ is constant at given conditions (e.g., water, air, light oils). Non-Newtonian fluids have a non-linear or rate-dependent relation (shear-thinning, shear-thickening, thixotropy, rheopexy). Viscoplastic materials (commonly referred to as “plastics” in older terminology) require a yield stress to initiate flow and then may behave Newtonian or otherwise.

Step-by-Step Solution:

Verification / Alternative check:

Examples: Water (Newtonian), ketchup/paints (shear-thinning non-Newtonian), corn starch in water (shear-thickening), drilling muds (Bingham plastic with yield stress).

Why Other Options Are Wrong:

Options (a), (b), and (c) are each correct; therefore (d) “All of the above” is the best single choice. (e) is false.

Common Pitfalls:

Confusing yield stress with yield strain; assuming viscosity is constant for all fluids; ignoring temperature dependence even in Newtonian fluids.

Final Answer:

All of the above