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I love to use everyday familiar items to explore complex scientific ideas. If you tell your kids that non-Newtonian fluid is a liquid with non-constant viscosity, they will probably yawn and forget. As scientists have discovered, we only retain about 5% of what we hear. If you introduce a relevant demonstration, the retention jumps to 30%, but learning by doing has the most remarkable effect. It leads to 70% retention and recall.
I first thought of making homemade peanut butter with my kids as a way to explore the changing states of matter: solid to liquid. When you take a handful of peanuts and apply a force on them by mashing them in a blender, you get butter, which is a liquid, right? Or is it?
If you take a jar of freshly made peanut butter and flip it upside down, would it all flow out? Nope! But if you scoop up a bit of peanut butter with a spoon and put it on your cracker, does it flow? You bet! If you try to eat it, it might even drip on your shirt.
So, it turns out that peanut butter is a great example of non-Newtonian fluid. One minute it behaves like a solid, and the next it flows like a liquid. Non-Newtonian fluids can switch between a solid and liquid state depending on the forces acting upon them.
Do you know what peanut butter, toothpaste, quicksand, and blood have in common? You probably have guessed it by now; they are all examples of non-Newtonian fluids!
Do you want to join us in making peanut butter while learning about states of matter and non-Newtonian liquids? All you need are peanuts!
Peanut Butter InvestigationTake a spoon of water and a spoon of peanut butter. Pour it out (or try to). Which one acts more like a liquid? (Answer: water)Put a spoonful of peanut butter on a plate. Put a peanut (or other nut) on another plate. Push on each with an index finger. Which one acts more like a solid? (Answer: nut)Scoop a spoonful of peanut butter out of a jar. Note the difficulty with which it was done. Now, with a spoon, vigorously stir the rest of the peanut butter in the jar for a minute. Scoop another spoonful of peanut butter. Did it become easier or harder to scoop it out? (Answer: easier)Simple Viscosity Experiment. Take two jars of peanut butter (we put them in the fridge after blending): one smooth, the other with chunks of nuts. Do a series of experiments to see which one flows more easily. You can scoop it with a spoon, spread it on toast, and flip a jar upside down. (Answer: the more chunks of nuts in the butter, the more like a solid it will act).Temperature experiment. Take three pieces of bread. Put one piece on a plate in a fridge. Toast the second piece. And leave the third one at room temperature. Spread the same peanut butter on all three pieces. Which toast has the runniest butter? (Answer: the toasted slice, if you applied butter while it was still hot).Comparison experiment.
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If you made more than one flavor with us, do this simple experiment. Scoop a spoon of each and turn them over your plate (or over your open mouth if you’re very patient). Which one takes longer to flow out? The more it resists the flowing motion, the higher the viscosity. (Note: If you didn’t do a different flavor, you can use a jar of store-bought peanut butter for comparison).
Are you interested in learning more about viscosity? We recently did a fun experiment to compare the viscosity of maple syrup, honey, ketchup, and thickened pie filling. Stay tuned!