GED Science TestPhysical ScienceMedium
A student is investigating the properties of a non-Newtonian fluid, such as cornstarch and water. When the fluid is stirred slowly, it flows like a liquid. However, when a strong, sudden force is applied (e.g., punching it), it behaves like a solid. This behavior demonstrates that the fluid's viscosity is dependent on which of the following?
- ATemperature.
- BShear rate.
- CPressure.
- DVolume.
Show answer & explanationAnswer & explanation
Correct answer: B. Shear rate.
Non-Newtonian fluids like cornstarch and water exhibit viscosity that changes with the shear rate (how quickly it's deformed or 'sheared'). A slow shear rate (stirring) allows it to flow, while a high shear rate (punching) makes it resist flow like a solid.
Why the other options are wrong
- A. While temperature can affect viscosity, the scenario specifically describes behavior based on the speed of applied force, not temperature changes.
- C. Pressure can affect some fluid properties, but the described phenomenon of 'punching' relates to the rate of deformation, not just static pressure.
- D. Volume is a measure of space occupied and does not directly influence the viscosity behavior described in the scenario.
Non-Newtonian Fluid Viscosity
A fluid whose viscosity changes depending on the applied shear rate or stress, unlike Newtonian fluids where viscosity is constant.
- Examples include cornstarch and water (oobleck), ketchup, paint.
- Can become thicker (shear-thickening) or thinner (shear-thinning) with increased shear.
- Viscosity is not a constant value for these fluids.
Memory trick: Non-Newtonian fluids are 'moody' – their flow depends on how you treat them.