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We are chemical engineers at North Carolina State University, working on non-Newtonian fluids, soft matter, and biomaterials. We test out your favorite ideas with real experiments and report back in Part 2 of this virtual lab event. AUA!
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Hello Reddit! We invited your burning questions about non-Newtonian fluids in Part 1 of our lab’s AMA series last year, promising to test the most interesting ideas with real experiments. The time has come for us to release our results to these popular questions! 1) Can oobleck (shear thickening fluid) be used for the best kind of speed bumps? (Credit: /u/slp50) ANSWER: Yes! Turns out /u/slp50 had the best idea all along. Experiment: We drove a remote controlled car over two different types of oobleck speed bumps at different speeds. The resultant video itself not the most interesting, but we analyzed the vertical acceleration of the car in slow-mo, and the analysis shows some really exciting results! When we compared our data with people driving their cars over all kinds of road speed bumps in 1973 (source: G. R. Watts, Transport and Road Research Lab Report, 1973), we find that non-Newtonian speed bumps are actually MORE COMFORTABLE AT LOW SPEEDS! And on the flip side, they are really uncomfortable if the car exceeds a certain critical speed! So, this idea is a winner. 2) What happens if you shoot ultra-strong sound waves into oobleck? (Credit: /u/ittimjones) ANSWER: The water inside the oobleck ends up quickly separates from the solid particles, and the entire non-Newtonian fluid expands. See our experimental video here. 3) What happens if you inject oobleck onto oobleck, or drop other non-Newtonian fluids onto themselves? (Credit: /u/bangbangIshotmyself) ANSWER: This one was really hard to do experimentally, so we changed it just a bit: we injected colored water into a normal liquid, a transparent gel that flows kind of like ketchup (yield stress fluid), and oobleck (shear thickening fluid). The gels lock the injected fluid in place, while oobleck “spits out”, or phase separates, the injected fluid. Check out our experiment here. 4) What if we drop a ball in these fluids? (Credit: /u/Croanius) ANSWER: We tried two types of non-Newtonian fluids: a liquid gel made of clay, and our cornstarch oobleck. Balls get stuck in the gel, and balls bounce on oobleck. Did you know that the army uses gels to test the effect of ballistics on humans, because no matter how much we work out, our bodies are basically jello? You can check out our results of dropping a ball into non-Newtonian fluids here. 5) Is full fat mozzarella cheese really necessary for the best kind of pizza (where the cheese is stretchy)? (Credit: /u/voilsb) ANSWER: For pizza connoiseurs: Yes, you must use full-fat mozzarella cheese if you want to reproduce that stretchy cheese phenomenon found in Pizza Hut commercials. We tested full-fat and skim-milk mozzarella, and the full-fat moz stretches extremely well above 80°C (175°F). See our experiment here. 6) Are cats non-Newtonian fluids? (Credit: Dr. Goulu) ANSWER: YES! But it depends on the situation and mood of the cat. Hear it from the IgNobel Physics prize winner! Tell us what you think about these experiments, non-Newtonian fluids, or just science life in general. Our lab members will be here to answer your questions all day.