A Scientifically Vexing Condiment
Simply tilting a ketchup bottle is sufficient to induce its contents to flow out… eventually, but science has demonstrated that there are fewer than 17 humans alive today who possess adequate patience for that method. The other several billion of us are quickly and invariably driven to shocking acts of violence, repeatedly buffeting the bottom of a bottle to compel a splat of red ejecta, or stabbing a knife up its neck and forcibly extracting a dollop. We don’t put up with this from our other condiments. What’s ketchup’s problem?
It is a non-Newtonian fluid, like latex paint, toothpaste, blood, xanthan gum solutions, and some printer inks.
Most fluids are Newtonian and all alike since their viscosity is independent of stress. Non-Newtonian fluids (NNFs), on the other hand, are defined by odd reactions to stress. Some become more viscous, while others become less so. Some change viscosity depending on how much or how long the stress is applied. When stress is applied to any NNF, the fluid develops internal layers that each has a different viscosity.
Oobleck, a simple combination of corn starch and water named after a goo in a Dr. Seuss book, is a common homemade alternative to Play-Doh and an NFF. The memory of playing with Oobleck led an Air Force researcher in 2017 to experiment with different NNFs to create armor. The Air Force discovered at least one NNF that hardens so thoroughly and quickly in response to great forces that it can literally stop bullets.
That explains why ketchup seems almost willfully recalcitrant to exit its container, but it helps naught with the extraction. Every ketchup maker has figured out that if you put ketchup in a plastic bottle and squeeze, the column of ketchup along the central axis of the bottle is the least viscous and squirts out easily. For those of you eager to flaunt your grasp of NNFs, however, there’s a new trick to dealing with glass bottles of ketchup.
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