Liquids that break the rules of physics
Non-Newtonian fluids are materials that don't follow Newton's law of viscosity. Unlike water or oil, their viscosity (thickness) changes based on the force applied to them or over time. They seem to defy intuition—turning from liquid to solid in an instant, or flowing more easily when stressed.
These fascinating substances are all around us, from ketchup and toothpaste to quicksand and blood. They showcase the remarkable boundary between different states of matter and have numerous practical applications in fields ranging from food science to military technology.
These fluids increase in viscosity when stress is applied. The classic example is oobleck (cornstarch and water), which allows you to run across its surface but will sink you if you stand still.
Examples: Cornstarch solutions, silly putty under impact, concentrated particle suspensions.
These fluids decrease in viscosity when stress is applied. They flow more easily when you apply force.
Examples: Ketchup, paint, blood, many polymer solutions.
These time-dependent fluids become less viscous over time when shaken, agitated, or stressed, and then thicken again when allowed to rest.
Examples: Yogurt, quicksand, some clay suspensions, printer ink.
These rare, time-dependent fluids increase in viscosity the longer stress is applied. The opposite of thixotropic fluids.
Examples: Some lubricants, cream whipped for extended periods, gypsum suspensions.
These fluids behave as solids at low stress but flow as viscous fluids at high stress. They have a yield stress threshold.
Examples: Toothpaste, mayonnaise, drilling mud, certain cosmetics.
The unusual behavior of non-Newtonian fluids emerges from their microstructure. Most contain particles, polymers, or other components suspended in a liquid medium.
These mechanisms create the fascinating transition between solid-like and liquid-like behavior that makes non-Newtonian fluids so counterintuitive and useful.
Shear-thickening fluids are used in liquid body armor. Under normal conditions, these materials remain flexible for comfort. Upon impact (like a bullet or knife), they instantly harden to absorb and distribute energy, providing superior protection while maintaining mobility.
Non-Newtonian properties are crucial in food processing and formulation:
Shear-thinning fluids make ideal 3D printing materials. They flow easily through the nozzle under pressure but maintain their shape after deposition, allowing for complex structures to be built layer by layer without collapsing.
Blood is a non-Newtonian fluid, thinning when flowing quickly through arteries and thickening when flowing slowly through capillaries. Understanding these properties is crucial for treating circulatory disorders and designing artificial vessels.
Click or tap the oobleck pool below. The harder/faster you tap, the more resistance you'll encounter!
Drag the circle through different fluids and feel how they respond differently to your movements.
Watch how the fluid behaves and identify which type of non-Newtonian fluid it is.
Let's see how much you've learned about these fascinating fluids!
Can you match these everyday products with their non-Newtonian fluid type?
If you want to learn more about non-Newtonian fluids, here are some great resources: