Moment of Science: The Falling Cat Conundrum

“...And he sticks the landing!”
Ever wonder why cats always seem to land on their feet? Take a journey through physics history in this week's Meowment of Science!
Published: Nov. 16, 2021 at 4:51 PM EST
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It’s a physics problem that baffled scholars for centuries, and it all has to do with our feline friends! Let’s take a look through physics history at why cats always seem to land on their feet.

* A French doctor, Etienne-Jules Marey (1830-1904) invented a “chronophotographic gun”, to (somewhat literally) shoot its target at 12 frames a second. That allowed him to capture movement and print it all on a single slide. In his pursuit of science, Dr. Marey ended up producing the first-ever film of one of our feline friends (Falling Cat, 1894)... call it the forefather of the endless supply of cat memes. It’s that rotation back to a safe landing that really puzzled 19th-century researchers.

* It all has to do with angular momentum, or how an object spins around an axis. The conservation law states that you can only change that momentum if an external force acts on the object... like a figure skater pulling their arms in to spin faster around their axis, or air resistance for a skydiver. (In case you couldn’t tell, skydivers need a lot more leeway than a falling cat.) A lot of physics treats objects as “rigid bodies”... but neither humans nor cats are exactly rock-solid, and that was one problem with the falling cat conundrum all along. They bend their bodies so both halves rotate around different axes, and here’s the cool part: they tuck in their front legs like a figure skater, but extend their back legs... then, once there’s enough difference in rotation, they reverse their leg positions to level out for a safe landing!

* We now know it as the “righting reflex”, or “cat-turning”, and most cats start to develop it within their first month. With a flexible backbone and detached collarbone, cats are uniquely qualified to save themselves from a painful fall. Some recent papers have posited that, with a combination of terminal velocity and flexible bone structure, cats are more likely than not to survive falls from up to 7 stories high -- but not without severe risk of injury all the same.

* By the way, that cat from the 1890s led to perhaps the best line ever published in a scientific paper: “The expression of offended dignity shown by the cat... indicates a want of interest in scientific investigation.” (Nature, 1894)

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