The Physics of Dogs and Cats Lapping Water

In 2010, MIT performed a study looking at the way that cats lap up water. Up to this point, it was believed that both dogs and cats formed their tongue into a “scoop” and brought the water to their mouths in this fashion. (http://www.youtube.com/watch?v=63Ch2pNkZwU)

However, one researcher realized that cats utilize a completely different technique. Instead of forming a scoop, cats will ever so slightly bend their tongue tip back and touch it to the surface of the water. Inertia and the cohesion of the water molecules enables the liquid to be drawn up into the cat’s mouth in a column. At a certain point, the force of gravity becomes greater than the force of the inertia. At the instant where the strength of these forces switch, the cat knows instinctively to close its jaws and capture the maximum amount of water. A cat can lap water 4x/sec and never ceases to close its mouth at the exact same moment. The MIT researchers confirmed this by building a robotic tongue and altering its lapping speeds. (http://www.youtube.com/watch?v=ht9bPJDlRFc&feature=related)

In May of 2011, another study was published that confirmed the cat data, but also showed that dogs do actually utilize the same method as cats. An x-ray video was used to illustrate this point, and it was found that the only reason dogs are so much messier at drinking than cats is because they stick their tongues into the water further down than cats. (http://www.youtube.com/watch?v=12paEIC7BkU)