How do cats land on their feet?

When cats fall, they flip themselves rightside-up with seemingly little effort — which has perplexed scientists for decades. Our feline friends appear to defy the laws of physics by reconfiguring themselves mid-air without intervention from another force. So how do they do it?

Several factors affect how a cat is able to land on all fours, but simply put, there are two main forces at play: physics and neurology.

"One of the reasons that physicists were surprised that cats could rotate to always land on their feet is the conservation of angular momentum," Greg Gbur, a physicist at the University of North Carolina at Charlotte, told Live Science.

Essentially, this means that if something twists clockwise, something else has to twist counterclockwise. Imagine a cat falling from a stationary upside-down position. By bending at the waist, the cat can twist the front half of its body in one direction and the back half in the opposite direction. By the time it unfolds at the waist, the cat is rightside-up. Gbur dubbed this the "bend and twist" model in his book, "Falling Felines and Fundamental Physics" (Yale University Press, 2019). 

But there are other techniques that can help cats right themselves mid-air, and it's likely they employ more than one. In the "tuck and turn" method, a cat extends its front legs and tucks in its back legs, giving the backside a lower moment of inertia, meaning a lower amount of resistance to changes in rotational motion. Then, it does the opposite, tucking in its front legs and extending the hind legs. It has an effect similar to a spinning figure skater: Extending the arms out wide increases the moment of inertia, while drawing the arms close to the body decreases it. This inversely correlates with speed. As inertia goes up, speed goes down, and vice-versa. Cats can also use what Gbur calls "the propeller tail," which works similarly. As the tail spins in one direction, the body can rotate in the other. 

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Such contortions are possible thanks to cats' flexible lumbar region — the space between their pelvis and ribcage — John Hutchinson, a professor of evolutionary biomechanics at the Royal Veterinary College at the University of London, told Live Science. Cats have skinny vertebrae, which makes them more flexible than other four-legged vertebrates.