Grade 7-9 Any questions?Fluid ReachMechanics out [email protected] Nifty Non-Newtonian Fluid Campers will learn about non-Newtonian fluids then have the chance to make their own! Materials Safety Considerations ● Water Take care when disposing the oobleck ● Corn starch fluid. ● Bowl Key Words Fluid: any substance with no fixed shape that flows or deforms under applied shear stress. Can be a gas, liquid, or plasma. Newtonian fluid: a fluid with a constant viscosity, such as water or gasoline. The viscosity of a Newtonian fluid only changes with changes in temperature or pressure. Non-Newtonian fluid: a fluid which changes its viscosity when the forces on it change. It does not follow Newton’s law of viscosity. A non-Newtonian fluid’s viscosity can change when under force to either more liquid or more solid. Viscosity: measure of a fluid’s resistance to change shape, sometimes in reference to the ‘thickness’ of the fluid. Nifty Non-Newtonian Fluid Most of the fluids you first think of are probably Newtonian fluids. These are “regular fluids” that have a constant viscosity at constant temperature and pressure. This means that at constant temperature, the liquid stays the same “thickness” no matter if any forces are applied to it. There is another type of fluid called a “non-Newtonian fluid”, that doesn’t follow the regular rules of viscosity. There are different types of non-Newtonian fluids. Non-Newtonian fluids have a lot of interesting properties, and we are going to explore those today! Can you think of any non-Newtonian fluids? Some examples of different types of non-Newtonian fluids are listed below. Try to think of at least one fluid for each type! a. Viscosity decreases (fluid gets “thinner”) with stress over time (this is called “thixotropic”). i. Example: honey (if you stir solid honey for a long time, it becomes liquid honey) b. Viscosity increases (fluid gets “thicker”) with stress over time (this is called “rheopectic”). i. Example: cream (if you stir cream for a long time, it becomes more solid and becomes whipped cream) c. Viscosity decreases (fluid becomes “thinner”) with increased stress (this is called “shear thinning”). i. Example: ketchup (if you shake ketchup, it becomes thinner) d. Viscosity increases (fluid becomes “thicker”) with increased stress (this is called “shear thickening”) i. Example: oobleck (cornstarch and water - becomes thicker or almost solid-like if you apply force) Nifty Non-Newtonian Fluid Steps: One popular non-Newtonian fluid can be made out of just two ingredients: cornstarch and water (this is also called oobleck). We are going to make some today! 1. Oobleck is very simple to make: in a large bowl, combine 2 parts cornstarch to 1 part water and stir to combine. You can add more or less cornstarch and water once you have stirred to get your desired consistency (you should be able to press a handful of oobleck into a solid-ish ball when you squeeze it in your hand, but when you open your hand it should turn back into a liquid, almost like it is “melting”). 2. Make some observations about this non-Newtonian fluid. What happens when you apply pressure (i.e. squeeze it into a ball)? Is it more solid- or fluid-like when you apply pressure? What happens when you decrease the pressure (i.e. open your hand)? Is it more solid- or fluid-like when you decrease pressure? 3. Try a few things out with the oobleck, like punching the mixture. What does it feel like when you hit it? Does your hand go through? Does it feel more like a solid or a liquid? Then, try slowly putting your hand in the mixture. What happens when you try putting your hand in slowly? 4. Try stirring the oobleck. Is it easy or difficult to stir? 5. Experiment to see if materials sink or float in the fluid. Make hypotheses before each test! Debrief: What happened when you tried the suggestions above with your oobleck? Can you think of any other substances that act like this non-Newtonian fluid? Why do you think this occurs? When you apply pressure to oobleck, it forces the cornstarch particles together and traps water molecules between them, which temporarily increases the viscosity (becomes thicker, almost like a semi-solid). When oobleck is at rest with no pressure applied, the water molecules surround the cornstarch particles and act as a lubricant which allows the starch grains to flow freely (becomes thinner). #SVatHome Want to share your project or results with us? Email or tag us @ScienceVenture Have a question? Reach us at [email protected].