Why Do Cats Always Land on Their Feet?

As long as there have been little kids and curious scientists, people have been dropping cats to see what happens. And for just as long, cats have landed on their feet. But how do cats pull this off? The answer to that question has been a scientific query for hundreds of years. 

Do Cats Always Land on Their Feet?

In his 2019 book Falling Felines and Fundamental Physics, Greg Gbur, a physics professor at the University of North Carolina Charlotte, gives a delightful tour through the history of the science of falling cats (with fascinating detours into related history and science). According to Gbur's accounting, the problem has intrigued and vexed scientists since the 1700s.

By the mid-1800s, the basic laws of motion had been established; it was assumed that the law of conservation of angular momentum meant that an object in free fall needed something to push against to give it initial rotation. In other words, a cat couldn't just flip itself in space after it began falling. It must have been pushed off a tree limb or the hands of the person dropping it.

Then in 1882, French scientist Étienne-Jules Marey developed a technique called chrono-photography and used it to photograph a falling cat at 12 frames per second. The resulting images clearly showed that the cat could right itself in mid-air without pushing off anything. When Marey presented his findings at a meeting of the French Academy of Sciences in 1894, the reaction was intense. It seemed that Marey had presented evidence that contradicted the laws of physics.

It turns out, however, that the initial study of angular momentum was limited to rigid bodies. Cats are anything but. Cats are soft, cuddly, supple things. The flexibility of a cat's body makes it capable of pulling off these mid-air gymnastics.

Finding Out How Cats Land When They Fall

Scientists quickly realized their mistake, and soon an explanation was proffered. French mathematician Émile Guyou proposed a solution endorsed by Marey and accepted by most of the members of the Academy. In a manner similar to ice skaters pulling in their arms to spin faster or stretching out their arms to slow down, cats used the position of their front and back legs to control their spin.

(Credit:Étienne-Jules Marey, Public domain, via Wikimedia Commons/) {{PD-US}}

When a cat first falls, Guyou suggested, it extends its rear paws and tucks in its front paws. This allows it to twist its upper body without much counter-twist from the lower body. Then the cat tucks its rear paws, extends its front paws and twists its lower body into the desired position without much counter-twisting from the upper body. Gbur calls this the Tuck and Turn model, and it was fine as far as it went. 

Ongoing Debate Of Cat Gymnastics

Then in 1935, a team of Dutch physiologists, G. G. J. Rademaker and J. W. G. ter Braak, took another look at Marey's photos and noticed something others had missed. When cats start to fall, they arch their backs, bend their bodies in the middle, then rotate the two halves in opposite directions. The front part and the back part are essentially two cylinders rotating in opposite directions. The angular momenta of the two turning parts of the cat's torso offset each other, resulting in an angular momentum of essentially zero. When the cat straightens back out, it will have flipped over. This is called the Bend and Twist model of cat turning.

But even that is not quite the final word. There are many different motions that come into play when a cat is falling, says Gbur, and there are many cats with individual personalities. "Each cat probably does their own little twist on it."

And there are many scientists, too, each with an individual personality. Gbur says he sees the "Falling Cat Problem" as something like a Rorschach test for physicists. When looking at films of falling cats, "everybody kind of sees what they want to see. If you're looking for Tuck and Turn, you'll probably notice the motion of the limbs more. If you're looking for Bend and Twist, you're probably going to spot the folding and the twisting of the body."

Despite small distinctions in form, the physics of the falling cat problem is more or less solved. At this point, says Gbur, the remaining questions are more about the neuroscience involved — how the brain senses the fall and the rotation.

Don't Try This at Home

Gbur offers a word of advice to amateur scientists who are interested in the physics of falling cats: "Please, please don't drop your cats. All cats presumably have this reflex, but not all of them are very good at it. And there are plenty of videos online of falling cats that you can look at and study."

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