The Physics Behind Your Cat’s Tongue

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Cats like doing things their way, even when it comes to something as simple as drinking water. Researchers recently discovered that cats have their own style when it comes to lapping up water. Their tongues are capable of performing one of the most complex maneuvers that pits inertia versus gravity in a delicate balance.Surprisingly, science has little to offer on the physics involved behind lapping. Dogs, and many other animals, have incomplete cheeks which makes them incapable of sealing their mouth to produce enough suction. They curl up their tongues into a ladle-like shape to scoop up all the liquid. Up until now, researchers had erroneously assumed that cats tend to do the same, albeit with raspier and smaller tongues. But researchers from MIT started to question the assumption and wondered whether there was more to their dainty drinking than met the eye.Over time, they filmed over ten cats with a high speed camera. To their surprise, they discovered that cats tend to rest their tongue tips on the surface of the liquid without penetrating it. The water stuck to the tongue of the cats and was pulled upward as they drew their tongue into their mouths. When they closed their mouth, it created a break in the liquid column while simultaneously keeping the whiskers and the chin dry.It is a much more well-controlled and delicate mechanism than the run-of-the-mill lapping. But the physics behind it is delicate in its aspect. To understand the mechanics behind it, the physicists built a prototype of a robotic tongue with the aid of a glass disk with the same dimensions as that of the cat tongue. They calibrated the disk to move up and down over the surface of the liquid, breaking and making contact with the surface while trying on different lapping speeds.They came to the conclusion that the lapping balances the tendency of the liquid to keep moving upward as the cats drew their tongue in, against gravity, which is responsible for drawing the liquid back into the bowl. Basically, if they want to have a satisfying drink, then they must lap faster to keep the gravity from overtaking the inertia. Timing is the key, as the column of the water is at its thickest and longest before gravity has its say and pulls the column down. Surprisingly, the cats seemed to know the speed at which they should lap. If they closed their jaws sooner, they would miss out on some of the water. If they closed it later, they would lose the entire column.So far, this behavior has been observed only in felines, but robots are soon set to join their ranks. Soft robots could mimic the natural behavior of the cats and give robotics experts a fresh way to approach the problems that require a delicate handling of the liquids.