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!
Abstract
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.