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Cats and dogs have it tough: They can't use straws, or tip a cup up to their mouths to drink. Instead, they have to use their tongues and a few different physics tricks to quench their thirst.

Hosted by: Olivia Gordon
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Olivia: You might have noticed how cats delicately lap up milk, while dogs will head over to a water dish and sloppily splash all over your floor. Turns out, there’s some interesting physics to back up the phrase, “cats rule and dogs drool.” That’s because these pets have to use their tongues to get liquids into their mouths, fighting against the effects of gravity. And, according to a couple research studies, cats and dogs have slightly different techniques that do or don’t make a splash.

You and I can sip our milkshakes and soups thanks to suction. And animals like horses, pigs, and sheep can suck up their water, too. And that’s because we all have complete cheeks, which means we have muscles and tissues that let us seal our mouths and create a partial vacuum. Basically, you can make a pocket of lower air pressure in your mouth, so the water you’re trying to drink gets pushed up by the higher-pressure outside air. And that’s suction.

But cats and dogs don’t have cheeks like ours. Like lots of predatory mammals, they have incomplete cheeks, which lets them extend their jaws wider to chomp down on their prey. But they can’t create that partial vacuum and suck up liquid. Instead, they use their powerful tongues to create columns of liquids like water or milk, and lap it up.

Using slow-motion video, different groups of researchers have tried to figure out the physics behind the tongue movements of cats and dogs. One study found that cats lower the tips of their tongues to just barely touch the surface of the water. Then, they quickly retract their tongues at speeds of almost 80 centimeters per second.

The water molecules stick to the cat’s tongue thanks to adhesive forces, and stick to each other because of cohesive forces. And this creates a column of water for a split-second, fighting against the force of gravity.

Dogs, on the other hand, are a little more gung-ho than cats, according to a separate study. These researchers found that dogs splash their tongues deeper into water bowls, curl them into more of a ladle-shape, and then can retract them at speeds of 700 centimeters per second or more.

This means more of a dog’s tongue is touching the water, so dogs end up making a bigger, messier water column before they clamp their mouths shut. The larger the dog, the larger the tongue, and the larger the splash. So next time your dog makes a mess at the water bowl... you can blame physics.

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