Saturday, November 12, 2016

The Puzzling Physics of Falling Cats


Falling Cat: Karin Brulliard writes for The Washington Post that the question of falling cats made it into a journal article in 1969: “A year later, Kane and a colleague published what remains the definitive examination of the topic: A paper titled A Dynamical Explanation of the Falling Cat Phenomenon” — which probably brought the first and only cat photos to the pages of the International Journal of Solids and Structures.”
Photo Credit: Ralph Crane; International Journal of Solids and Structures, 1969, Vol. 5

An article, by Karin Brulliard, in The Washington Post examines a scientific question that on first glance seems of no scientific importance, and yet it does, as this post shall soon elucidate. The question is simply this: how is it that falling cats tend to always land on their feet when dropped from a particular range of heights—typically between two and six feet? Many of us have seen cats do this; and it happens so quickly that we view this feline feat with awe.

Yet, it is not only cat lovers who wonder about this, but also those with more particular scientific bents of mind. How cats turn themselves right has long interested and baffled the best scientific minds, including those of  George Gabriel Stokes, the University of Cambridge’s Lucasian Professor of Mathematics; and James Clerk Maxwell, whose equations on electromagnetism are widely used today.

Serious scientists have taken up the mantle, including Greg Gbur, a physics professor at the University of North Carolina Charlotte, writes Bruillard, “who has blogged about what is now known as the cat-righting reflex.” In “Scientists just can’t stop studying falling cats” (November 4th, 2016), Brulliard sheds light on the continuing scientific fascination with falling cats:
That’s because while this feat of kitty gymnastics is a useful instinct for animals that climb trees, it’s also a physics conundrum — one that has occupied photographers, scientists and even NASA over the many decades since Stokes and Maxwell dropped felines. (Yes: Cats are even more mystifying than we knew.)

The issue is that the cat flip appears to violate the law of conservation of angular momentum, which says that when one thing rotates, something else rotates with equal and opposite angular momentum in another direction. Put more simply, Gbur said, when you push on the pedals of your bike and make its wheels rotate, the wheels push the surface of the Earth below with an equal force in the opposite direction (though the planet is way too heavy to actually move). But the cat is dropped with nothing to push off of — with no angular momentum to start with — and rotates all the same.
Scientists still haven’t reached a consensus on the math and physics behind the twisting and turning, which allows these mysterious felines to land on their feet. Brulliard writes in the same article:
“Probably the cat uses multiple different strategies to turn over,” Gbur said. “Physics prefers and tends to look for the simplest possible explanation for a phenomenon, whereas evolution — if I anthropomorphize it — is always looking for the most efficient. Living creatures are doing whatever works best, which may not be the simplest option.”
No one told the cat of its lack of scientific understanding, and yet it is successful. There is something to be learned here. As for curiosity, scientific or otherwise, I admit that when a cat resided with me, and I was a single guy working as an engineer, I did the test myself, dropping my cat from a height of three or four feet; he always, without failure, landed feet first on my living room carpet. Periodically, I would revisit this experiment, always impressed by his athletic abilities.

The last time, however,  he was slightly upset (I could tell by “his look”) , so I discontinued the experiment. I have not dared to drop a cat since then. My scientific curiosity was satisfied, but more important was that I maintained a good relationship with my grey Persian cat and with all other felines.

For more, go to [WaPo]

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