Here's How Animals Go From Soaked To Dry In Seconds
Why study the proverbial wet-dog shake? Shaking when wet is a commonality among many furry mammals. Such a study provides shows insight into mammal survival, adaptation, and fluid mechanical phenomena which links numerous species.
Drop ejection from spinning disks is well-studied, but are the first to look at dripping from long fibers under accelerations higher than that of gravity.
Shaking mammals generate high centrifugal accelerations when spinning. A drop residing in a mammals fur will experience acceleration many times gravity when ejected. We found that mammals can generate accelerations 10-70 times gravity in their fur when shaking.
Why do mammals shake when wet? The simple answer, as you may guess, is to dry. Perhaps a better question is why an animal wants to be dry. According to our calculations, a wet animal could spend 20% or more of its daily food energy to evaporate water in its fur, if it cannot shake.
In our study we found the largest mammals such as bears, tigers, and large dogs shake about 4 times per second while small mice shake at more than 30 times per second!
Smaller animals shake more quickly than larger animals. A certain spinning speed is required to remove water from fur. Larger animals have a size advantage and do not need to shake as vigorously to get their skin whipping fast.
Mammals' shaking is very effective. A shaking mammal can remove about 70% of the water trapped in its fur in few seconds, when fully wet. The remaining moisture content (RMC) in the fur is about 30%. When comparing the accelerations generated by animals to data gathered on our "wet-dog simulator" (see Methods below), we note that animals shake in the region where drying tapers off.
We found shaking longer or faster does not contribute to further drying. Therefore, mammals "tune" their shaking to achieve maximal dryness with the least effort.
The smallest animals lift their front paws to shake (full video).
Kunekune Pig: 8.2 Hz (full video)
Boer Goat: 7.7 Hz (full video)
Gulf Coast Sheep: 6.5 Hz (full video)
The kangaroo does not display the ability to shake the entire body. We think this is because of largest of the hindquarters and shape of the spine. Additionally, kangaroos live in hot and dry climates where shaking is of less priority (full video).
Small husky shaking: 5.8 Hz (full video)
Chocolate lab shaking: 4.5 Hz (full video)
Yellow lab shaking: 4.3 Hz (full video)