Fluid Classification — Definition of Non-Newtonian Fluid State whether the following statement is correct: ‘‘A fluid whose viscosity changes with the rate of deformation (shear rate) is called a non-Newtonian fluid.’’

Introduction:
Rheology categorizes fluids by how shear stress relates to shear rate. Newtonian fluids have a linear relation with constant dynamic viscosity mu. Non-Newtonian fluids deviate from this linear law; their apparent viscosity depends on shear rate and sometimes time, enabling behaviors like shear-thinning, shear-thickening, or yielding.

Given Data / Assumptions:

• Isothermal conditions; no phase change.
• Homogeneous fluid without large particles (unless considered as a suspension).
• Shear rate may vary over a practical range.

Concept / Approach:
Newtonian: tau = mu * (du/dy), mu constant. Non-Newtonian: functional relation tau = f(du/dy) with effective viscosity mu_app = tau / (du/dy) varying with shear rate. Examples include polymer solutions (shear-thinning), corn-starch mixtures (shear-thickening), and Bingham plastics (yield stress).

Step-by-Step Solution:
Examine the definition given.Compare with rheological laws: if viscosity depends on shear rate, it is non-Newtonian.Therefore the statement is correct.

Verification / Alternative check:
Viscometer data for paints or blood show viscosity decreasing with increasing shear rate (shear-thinning), validating the definition.

Why Other Options Are Wrong:
‘‘False’’ would imply shear-rate independence, which is the Newtonian case, contradicting the statement.

Common Pitfalls:
Confusing temperature dependence (all fluids have it) with shear-rate dependence; assuming time-dependent thixotropy is required—many non-Newtonian fluids are time-independent but shear-rate dependent.

Final Answer:
True