Understanding The Drinking Mechanics Of Cats And Dogs

Chuck Bednar for redOrbit.com – Your Universe Online
Both cats and dogs lap up liquids in much the same way. So why do canines spill so much more water than felines when they drink? As it turns out, there’s a valid scientific reason behind the phenomenon.
Researchers from Virginia Tech and Purdue University analyzed the drinking habits of various dog breeds, identifying the mechanics and modeling the fluid mechanics involved when dogs drink water. They found that the reason dogs create more backsplash is because they have the cheeks of a predatory quadruped.
The findings will be presented Tuesday at the American Physical Society’s Division of Fluid Dynamics (DFD) meeting in San Francisco, California, and builds on similar research previously conducted by the same team in which they used high-speed cameras to analyze the drinking habits of felines.
“Three years ago, we studied how cats drink,” Sunny Jung, an assistant professor at Virginia Tech, explained in a statement provided to NewsWise. In that November 2011 study, Jung and his colleagues reported that cats use their tongues to delicately draw up water without breaking the liquid’s surface, thus harnessing a perfect balance between the physical forces of gravity and inertia.
As Jennifer Viegas of Discovery News explains, neither cats nor dogs are able to suck in liquids the way humans do because their cheeks are designed for the lifestyle of a four-legged predator. While dogs are omnivores, the wolves from which they evolved are predators that typically hunt hoofed animals such as deer, moose, elk and caribou.
Like dogs, cats are members of the order Carnivora and have incomplete cheeks, allowing them to open their mouths wide enough to deliver the fatal blow to their prey. However, the same biological traits which make them effective hunters also makes it impossible to create suction while drinking. Since dogs cannot seal their cheeks completely, they are unable to create negative pressure and suck up water into their mouths like humans do.
Cats also lack suction, but they make up for it by drinking using a two-part “water entry-and-exit” process, the researchers explained. It compensates by just barely brushing the surface of water with the smooth tip of its tongue before drawing its tongue back in, forming a column of liquid between the tongue and the water’s surface. It then closes its mouth to pinch off the top of the column, using both gravity and inertia to keep its chin dry.
According to Reuters, when Jung and his colleagues started analyzing dogs, they expected to find that canines used a mechanism similar to their feline counterparts. However, they found that while cats gently touch the liquid surface with their tongues, dogs are far more aggressive and create more backsplash. Also, while felines pull up their tongue to create a water column with a force up to twice that of gravity, canines generate a force of up to eight times gravity.
The study authors also devised a model using glass tubes to simulate a dog’s tongue, which allowed them to alter the parameters of the experiment and mimic the acceleration and column formation during the exit process. Moving forward, Jung and his colleagues plan to study the diving dynamics of plunging seabirds, the skittering motion of frogs and the response of leaves to exposure to fast-moving raindrops.
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