Chris and I have been watching a PBS Nova series called “Making Stuff”. I love this series because it really breaks it down to a level that is simple to understand. We both learned a bunch of new interesting things and refreshed some existing notions. So I thought I’d share with you one tidbit of science today so you can be real popular at the next party.
The word of the day is: non-Newtonian fluids. Yay!
The resistant force of Newtonian fluids is linearly proportional to its flow. Try to move in it twice as fast will require twice the force. Water is an example of a Newtonian fluid. Newtonian fluids are what I would consider the intuitive fluids… It does what you expect. Its viscosity is dependent on its temperature only, not its flow.
Non-Newtonians fluids have a non-linear correspondence between viscosity and flow. What does this mean? Take for example ketchup. Put a bottle of ketchup upside down and the ketchup won’t come out. Jiggle a knife in the bottle and the whole thing comes flying out. It’s not just your luck, it’s because ketchup becomes more liquid when it is in motion! The knife doesn’t only force a clump to break off and fall down with gravity (which is what I always thought!), it actually sets the ketchup in motion and makes it more liquid in the process! In other words, its viscosity decreases as the flow increases.
As Missy Elliot would say, let’s “flip it and reverse it”. Not all non-Newtonian fluids become more liquid with flow, some work the opposite way. You might have done this experiment in high school: the right mix of cornstarch and water will be liquid at rest and solid when moved as its viscosity increases with its flow. That means you can walk on a pool of cornstarch and water, yet sink in it when if you go too slow.
Cool stuff right? So next time someone accidentally drowns their fries in ketchup, you can say “darn those non-Newtonians fluids!”