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The surprisingly complicated physics of why cats always land on their feet, Ars Technica

The surprisingly complicated physics of why cats always land on their feet, Ars Technica


      On the first day of Christmas –


Ars chats with physicist Greg Gbur about his book,Falling Felines and Fundamental Physics



         (****************************************A cat being dropped upside down to demonstrate a cat's movements while falling Enlarge/A cat being dropped upside down to demonstrate a cat’s movements while falling

Scientists are not immune to the alluringly aloof charms of the domestic cat. Sure,Erwin Schrödinger could be accused of animal cruelty for hisfamous thought experiment, (but Edwin Hubble)had acat named Copernicus, who sprawled across the papers on the astronomer’s desk as he worked, purring contentedly. A Siamese cat named Chester was even listed as co-author (FDC Willardwith physicist Jack H. Hetherington on a low temperature (physics paper in) ****************************************************************, published in Physical Review Letters. So perhaps it’s not surprising that there is along, rich history, spanning some 377 years, of scientists pondering the mystery of how a falling cat somehow always manages to land on their feet, a phenomenon known as “cat-turning.”

“The falling cat is often sort of a sideline area in research,” physicist and cat lover Greg Gbur told Ars . “Cats have a reputation for being mischievous and well-represented in the history. The cats just sort of pop in where you least expect them. They manage to cause a lot of trouble in the history of science, as well as in my personal science . I often say that cats are cleverer than we think, but less clever than they think. ” A professor at the University of North Carolina, Chapel Hill, Gbur gives a lively, entertaining account of that history in his recent book,Falling Felines and Fundamental Physics.The Over the centuries, scientists offered four distinct hypotheses to explain the phenomenon. There is the original “tuck and turn” model, in which the cat pulls in one set of paws so it can rotate different sections of its body. Nineteenth century physicist James Clerk Maxwelloffered a “falling figure skater” explanation, whereby the cat tweaks its angular momentum by pulling in or extending its paws as needed. Then there is the “bend and twist” (not to be confused with the “bend and snap“maneuver immortalized in the 2003 comedyLegally Blonde, in which the cat bends at the waist to counter-rotate the two segments of its body. Finally, there is the “propeller tail,” in which the cat can reverse its body’s rotation by rotating its tail in one direction like a propeller. A cat most likely employs some aspects of all these as it falls, according to Gbur.

********************************A cat being dropped upside down to demonstrate a cat's movements while falling
Cats are cautiously fond of physics, as Ariel can attest.**************************************** Ars Technica: What led you to write an entire book about the physics of falling cats?

************************************ (Greg Gbur) ******************************************: It really started with my love of the history of science and writing about it on my blog

. One day, I was browsing old science journals, and I came across (an) **************************************************************** paper

about photographs of a falling cat landing on his feet. I wrote a blog post about it. But I was not completely satisfied with the explanation, and I realized there were more papers on the subject. Every time I did a search, I found another paper offering another angle on the problem. Even in the last few weeks of writing the book, I still kept coming across minor little papers that gave me a little bit of a different take on the history. It was surprising just how many papers there were about the falling cat problem. The more you look, the more you find people intrigued by how a cat lands on his feet. It seems like a problem that would be readily solvable.

Ars: Surely one of the issues was that photography hadn’t been invented yet, particularly high-speed photography. (******************
************************************ (Gbur) : Yes. Maxwell did his own preliminary investigations of the subject, but he pointed out that when you drop a cat from roughly two feet, it can still land on its feet, even if you’re dropping it upside down. That’s a really short period of time. The human eye simply can’t resolve that. So it was a problem that was largely not solvable until the technology was there to do high speed photography.
****************************************** Étienne-Jules Mareydid the first High speed photographs of falling down. It was almost an afterthought for him. He was doing all these different high-speed photographs of different animals, because that was his research, studying living creatures in motion. He presented theimages of a falling cat (***************, and it genuinely shocked the scientific community. One of the members at the meeting where the photographs were presented, said (and I paraphrase), “This young Marey has presented us with a problem that seems to go against the known laws of physics.”The motions that are depicted in the photographs are quite complicated. The explanation given is part of the truth, but it seemed incomplete. It was good enough to convince physicists that a cat was not violating the laws of physics, but it was good enough to convince everyone that it was the right explanation, or the complete explanation.
Ars: You summarize four distinct hypotheses offered at various times to explain the phenomenon of cat turning. So what is the best explanation we have so far for how a cat can turn and fall and land on its feet?
************************************ (Gbur) : This is part of why it was such a challenge: all these different motions play a role. If you’re looking at a series of photographs or a video of a falling cat, it becomes almost a psychological problem. Different people, their attention is going to be drawn by different aspects of a motion. But the most important is a bend and twist motion. The cat bends at the waist and counter rotates the upper and lower halves of its body in order to cancel those motions out. When one goes through the math, that seems to be the most fundamental aspect of how a cat turns over. But there are all these little corrections on top of that: using the tail, or using the paws for additional leverage, also play a role. So the fundamental explanation comes down to essentially bend and twist, but then there’s all these extra little corrections to it.

What do you think?

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