Q.25 Which of the following fluids exhibit(s) non-Newtonian behaviour at 25 C?
(A) Toothpaste
(B) Mercury
(C) Brine
(D) Blood plasma
Understanding Non-Newtonian Fluids: Toothpaste, Mercury, Brine, and Blood Plasma at 25°C
Toothpaste exhibits non-Newtonian behavior at 25°C, making it the correct choice among the options. This article explores fluid rheology to clarify why.
Correct Answer
(A) Toothpaste shows non-Newtonian behavior as a shear-thinning fluid, where viscosity drops under pressure like squeezing from a tube. Options (B), (C), and (D) are Newtonian fluids with constant viscosity regardless of shear rate at room temperature.
Fluid Behavior Basics
Newtonian fluids maintain steady viscosity under varying shear rates, following linear stress-strain relationships. Non-Newtonian fluids deviate, often showing shear-thinning (pseudoplastic) or shear-thickening traits, common in pastes and suspensions. At 25°C, temperature affects these properties minimally for everyday fluids.
Option Analysis
| Fluid | Behavior at 25°C | Explanation |
|---|---|---|
| (A) Toothpaste | Non-Newtonian (shear-thinning) | Acts solid-like at rest but flows when squeezed; viscosity decreases with shear stress . |
| (B) Mercury | Newtonian | Pure metal liquid with fixed low viscosity; no shear dependence . |
| (C) Brine | Newtonian | Saltwater solution behaves ideally with constant viscosity . |
| (D) Blood plasma | Newtonian | Plasma (without cells) shows linear flow; whole blood is non-Newtonian due to cells . |
