Definition of Non-Newtonian Fluid
A non-Newtonian fluid is a fluid whose viscosity changes depending on the shear stress (force per unit area) applied to it. Unlike Newtonian fluids (like water or oil), which maintain a constant viscosity at a given temperature and pressure, non-Newtonian fluids can become thicker or thinner when agitated or subjected to external force.
Key Characteristics and Behavior
The defining characteristic is their variable viscosity. Some non-Newtonian fluids become more viscous (thicker) under increased stress, known as shear-thickening or dilatant fluids. Others become less viscous (thinner) when stress is applied, called shear-thinning or pseudoplastic fluids. This behavior often stems from the complex internal structure and interactions of the fluid's constituent particles.
A Practical Example: Cornstarch and Water (Oobleck)
A well-known example is Oobleck, a simple mixture of cornstarch and water. When gently poured, it flows easily like a typical liquid (exhibiting shear-thinning properties). However, if you hit it sharply or try to squeeze it rapidly, it instantly stiffens and resists deformation, behaving like a solid (displaying shear-thickening behavior). This dramatic change highlights its non-Newtonian nature.
Importance and Applications
Non-Newtonian fluids are critical in various industrial and everyday applications. Shear-thinning properties are desirable in products like paints, ketchup, and toothpaste, allowing them to flow easily when dispensed but remain stable otherwise. Shear-thickening fluids find uses in protective gear and certain manufacturing processes. Understanding these fluids is vital across fields from engineering to culinary arts and medicine.