A wet dog can teach humans some new tricks.
It may seem silly for scientists to study the way a dog shakes itself dry. But it could help engineers come up with automated-cleaning techniques to use in devices we can’t easily clean ourselves — like the insides of cameras or distant space rovers.
Georgia Tech researchers looked at the way wet dogs dry themselves and found that they can shake 70 percent of the water off their fur in four seconds, thanks to their loose hanging skin.
They used high-speed cameras to study the canines in motion. Key to a dog’s drying power: while its backbone can can only go 30 degrees in either direction, its loose skin can swing a full 90 degrees.
“The loose skin lets the dog whip much farther and faster to the left and the right. This results in three times the amplitude, three times the velocity and nine times the centrifugal force,” engineer David Hu told the Daily News.
With fellow scientists Andrew Dickerson and Zachary Mills, Hu now has suggested that one of the main reasons dogs evolved to have loose skin was this role it plays in fast drying.
Since water-saturated fur suffers insulation loss, developing a method for drying off quickly proved evolutionarily advantageous. The team also noted that most mammals developed the “wet dog shake” to dry off, so they wouldn’t deplete their energy unnecessarily. If mammals couldn’t shake (especially when the sun is not out), they would need to expend as much as 20 percent of their caloric intake to dry off by using body-heat alone, said Hu.
“If we tried to do this with our heads we wouldn’t have the musculature to do this,” Hu said. The dog’s body is particularly well suited for this shake.
After about four seconds, dogs stop shaking because the amount of water lost tapers off and the animals are attuned to getting the most dryness for the least amount of effort.
Not all animals shake at the same speed, either. To get rid of water, for example, mice shake more than 30 times per second. Large animals, like tigers and bears, need to shake only around four times per second, according to the team’s study.
Although generally demonstrable, a direct correlation between shakes-per-minute and size isn’t possible. That’s because a mammal’s hair-type also affects the amount of velocity needed to shake of water.
But not all mammals benefit from this evolutionary mechanism — or need to. Kangaroos, Dickerson explained, can’t shake their entire bodies because of the shape of their spines and the large size of their hindquarters. But there was no evolutionary advantage in it, so it didn’t matter, because they live in hot climates.
Down the road, the researchers think that there will be practical engineering applications for their work, for example, for optical devices, noted Hu, “like camera lenses or solar panels.” In other words, instruments that need to stay clean and dry and are often in hard-to-reach places.
mwalsh@nydailynews.com
