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  • This is the first live cat recorded on film, and it's being dropped to solve a physics problem: Why do cats always land on their feet?

  • It's a question that was driving 19th century scientists nuts.

  • Until one of them used an unexpected tool to solve the mystery: a camera.

  • Étienne-Jules Marey was an obsessive scientist and inventor who analyzed how things moved.

  • And he started experimenting with photography at a time when the medium was mostly used to document static subjects.

  • But his goal was to capture motion.

  • And he did that by building on a basic principle of photography: exposing a photosensitive material to light and then covering it in darkness.

  • So his way of creating this darkness and light was to have a disc with slots in it.

  • By controlling the light as the subject moved across the frame, Marey was able to record movement onto a single glass plate.

  • Essentially, all he does is block that light intermittently.

  • A slot from the disc opens, and then there's darkness as the man moves, opens, darkness.

  • This technique is called chronophotography, and the results show something human eyes will never see on their own: individual stages of motion.

  • A couple of years later, Kodak introduced celluloid film and Marey updated his slot camera in a crucial way.

  • He swapped the single glass plate with a roll of film that moved in between exposures.

  • So, light: an image is made.

  • Darkness, the film moves on.

  • Light, an imageso it's a movie camera, is what it is.

  • Marey made a lot of films for research purposes.

  • And even tried dropping other animals to see if they'd land on their feet, specifically this rabbit and this chicken.

  • Which brings us back to the cat.

  • It seems to be able to right itself by flipping in the air without pushing off anything first, which would contradict the law of conservation of angular momentum.

  • Sounds scary, but stick with me here.

  • One of Newton's laws of motion says that something in motion can't just stop itself unless an opposing force acts upon it.

  • Basically, you can't just change direction midair, Wile E. Coyote style.

  • But to the naked eye, it looks like a cat can.

  • Most people assumed the cat was "cheating" by kicking off the hands of the person dropping it.

  • But Marey's film showed what's actually happening.

  • The first few frames prove right away that the cat doesn't start its rotation from a kick.

  • But what it does do is arch its back.

  • And by arching its back, it's divided its body into a front part and a back part, and the two parts can work independently.

  • You know how a figure skater pulls their arms in to rotate faster?

  • That's whats happening here, too.

  • Early in the rotation, the cat pulls its front legs in and leaves the back splayed out.

  • So the front half can rotate quickly while the back half stays relatively still.

  • Then halfway through, it does the opposite.

  • Front legs stretched out, back ones tucked in to flip the other half of its body around.

  • And you notice by the time the cat is landing, all four legs are stretched out as far as they can be, which means slow rotation.

  • So the cat has rotated itself, but not overall; the two halves are working in opposite ways.

  • It uses the inertia of its own bodyweight to spin each side.

  • And because the two spins operate separately in opposing directions, they cancel each other out.

  • So Newton's law isn't broken.

  • Marey published his findings in Nature in 1894, breaking down the falling cat problem for the first time.

  • His work remains an early example of using photography for scientific discovery.

  • What does photography do for science?

  • It records something and it makes it permanent so you can analyze it later, or so you can share it.

  • But what Marey did was show something that the eye could not possibly seeever.

  • You might have seen another famous early example of motion photography.

  • In 1878, Eadweard Muybridge used 12 cameras connected to tripwires to prove that a horse lifts all four feet off the ground at some point in a gallop.

This is the first live cat recorded on film, and it's being dropped to solve a physics problem: Why do cats always land on their feet?

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B1 US Vox photography darkness motion film rotation

Why a cat always lands on its feet

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    Vivian Chen posted on 2019/06/21
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