… Memes referring to cats as liquid have been circulating online for several years. And they caught the eye of physicist Marc-Antoine Fardin of the Jacques Monod Institute, now at Paris City University and the French National Center for Scientific Research. “I spend some time on the Internet,” he said in a 2019 TEDx talk, “for research purposes, of course.” In the spring of 2014, Fardin began to scientifically study the fluid behavior of cats—a pastime that allowed him to avoid his real work. “This procrastination actually led to some success,” he explained in his talk. “It won me the Ig Nobel Prize of Physics, which rewards research that makes you laugh as well as think.”

The question is not so easy to answer. “If we wait long enough, everything eventually flows. That’s the motto of rheology,” Fardin said during his TEDx talk. For example, the solid asphalt of a sloping road continues to flow very slowly, which can be observed after several years or decades. Solids can also be deformed if enough pressure is applied to them. On the other hand, liquids can also have solid properties. Ketchup, for instance, only flows out of an open glass bottle after it has been shaken several times.

In work published in the journal Rheology Bulletin in 2014, Fardin had proposed that the relaxation time of young adult cats is between one second and one minute. This estimate allows the Deborah number to be calculated: if, say, a cat squeezes itself into a small cardboard box within five seconds and is observed for one minute, then De = 0.0833… That is significantly smaller than 1: the cat is clearly exhibiting fluid behavior.

In other words: this is actually an article about the fuzzy definition of solids/fluids, and how under this definition cats do, in fact, exhibit liquid properties

Article is from Scientific American and may have soft paywall