The physics of how wet animals dry themselves (w/ Video)

Oct 22, 2010 by Lin Edwards report

( -- Scientists using slow-motion movie cameras have been trying to discover the physics behind the "wet dog shake."

Physicist Andrew Dickerson of the Georgia Institute of Technology in Atlanta in the US and colleagues wanted to determine the optimal speed at which dogs and other hairy or furry animals should oscillate to shake water out of their fur most efficiently.

Dickerson’s team determined the conditions in which water drops are ejected by considering the balance of centripetal forces and surface tension on the drops. They likened the forces involved in the shaking or oscillating of wet, hirsute mammalian bodies to the spin cycle of a washing machine.

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Video credit: Andrew Dickerson

Centripetal force varies with the distance from the center of the body. Using this information, the team derived a mathematical model to calculate the optimum frequency of the , and their equation gave them a frequency value of R-0.5, where R is the radius of the animal. This means smaller animals must oscillate faster to generate enough force to shake off the water.

To test their model they filmed a wide range of wet dogs and other animals ranging in size from mice to bears, shaking themselves dry, and then used the video recordings to determine the period of oscillation of the shake. They supplemented the videos with fur-particle tracking and X-ray cinematography.

The value they found for labrador was around 4.3 Hz, and the frequency increased for smaller animals, with cats shaking at 6 Hz and mice at 27 Hz, while it decreased with larger animals such as a grizzly bear at 4 Hz. The relationship is not linear but the frequency asymptotically approaches a 4 Hz limit as the size of the animal increases.

Their results, pre-published on arXiv, also showed their equation was incorrect and the value for the frequency of oscillation is actually R0.75. Dickerson suggested the discrepancy may be due to their calculating the radius as being from the center of the animal to the skin, but he said "the fur might make a difference."

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More information: The Wet-Dog Shake, Andrew Dickerson, Grant Mills, Jay Bauman, Young-Hui Chang, David Hu, arXiv:1010.3279v1 [physics.flu-dyn]

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User comments : 19

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2.3 / 5 (3) Oct 22, 2010
Finally, the Navy can complete their dogship attack submarine. I'd love to have been there when Mr. Dickerson decided it was really a good idea to spend money and time on this
3.7 / 5 (3) Oct 22, 2010
You never know when these "Too much time on your hands" investigations find real world applications, plain curiousity and serenpedity are the stumbleupons of new science, that beind said, its allmost as good as filming funny animals with a hat, using a wide angle lens and the tune of the Benny Hill Show.
4 / 5 (5) Oct 22, 2010
I smell next years Ig Nobel Prize for Physics!
1.5 / 5 (16) Oct 22, 2010 never know when these "Too much time on your hands" investigations find real world applications...
Definitely before the applications of cold fusion research. Some prioritization is required even in science - the free market for scientific ideas is still poorly established. We cannot spent all money in research of remote side of Pluto only just because it's feasible.

The worse problem is, the model presented is very rough, because it neglect inertial forces resulting from shaking motion reversal and decreasing of surface tension forces resulting from gluing of fur with droplets of water.

It's solely academic toy, the only purpose of it is to score at next IG Nobel competition, which is gaining increasing popularity during recent years.

Which is what counts not only in MTV - but in contemporary physics, too.
4 / 5 (4) Oct 22, 2010
Was tax revenue spent on this?
I would suggest a review of the study approval process and personnel. If this is the state of university recource utilization, we need to step back and reevaluate what we're spending our efforts on. This is no joke.
1.3 / 5 (15) Oct 22, 2010
It shouldn't be so difficult, it's appears like school research project. Mr. D.L. Hu is a professor. Such research can serve for educational purposes primarily (most of authors are undergrads) - but I can still imagine more serious and useful research even at schools.. And why five authors are involved in such stupidity? Apparently an attempt to collect impact factor - scientists are payed for number of publications, so that every article counts in CV..
4 / 5 (5) Oct 22, 2010
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I suppose that would be called a spin-off product of the research? lol
3.2 / 5 (5) Oct 22, 2010
I do some research in droplet formation for aerosol applications. This effort does have value, regardless of the jokes and comments.
3.3 / 5 (4) Oct 22, 2010
I think they missed the relevant question. How do animals shake all that water off and not get dizzy? Have you ever tried to shake out your hair after a shower?
5 / 5 (2) Oct 23, 2010
This research may be stupid, but it is valuable. Physics and related areas of science are unique because results tend to be "application agnostic," in the sense that findings are usually mathematical in nature and can be applied to any system with similar physical characteristics.

If you've ever wondered how a drug company can fabricate coated medication pills with a consistent and uniform outer layer, look no further than the present study. The way that this is typically accomplished in industry is that thousands of uncoated pills are placed into a large drum, the coating is added in liquid form, and the drum is spun slowly (to coat the pills) and then quickly (to whisk off extra coating). As far as I know, there are no furry pills, but, considering the scale of most industries in existence today, finding a single application for research like this is likely to generate millions of dollars in revenue (and enough tax income to compensate for the research and beyond).
1 / 5 (13) Oct 23, 2010
finding a single application for research like this is likely to generate millions of dollars in revenue
Yes, but currently it has no meaning. The question is, why to do such research in advance when it could be done in much easier, exact and cheaper way at the moment, when some application would exist for it.

At the case of some cheap silly dog shaking research such question remains academical, but at the case of collider experiments it gains relevancy. Currently we have no usage for any particle revealed in colliders before seventy years, so it's quite probable, we would have no usage for them during next fifty years. If so, why to spend a money into such research and why we cannot invest into cold fusion research, for example? I'm not saying, basic research is wrong, but prioritization of research is important too. We should realize, many branches of research are a remnants of cold war and competition between USA and Russia and we have actually no usage for it.
1 / 5 (13) Oct 23, 2010
The players of Civilization, Age of Empires and/or other strategic games know very well, it has no meaning to invest resources into research, which doesn't correspond the usage of its results in given epoque.

It seems for me, the physicists as a whole become a lobbistic group separated from needs of society: they don't care about useful research (cold fusion, antigravity machines, Bedini electromotor, room temperature superconductivity) - but they're asking huge money for confirmation of existing abstract numerologic models (Big Bang, Higgs boson in Standard model) just because it enables them to write another useless publications. They've no feeling for their actual significance and usefulness like social cancer and layman people, who are entertained with their experiments with shaking dogs actually do not realize it.
1 / 5 (13) Oct 23, 2010
In this context it's symptomatic, the teachers of physics (who are often serving as a priests trying to preserve the established status quo in physics) are getting most impressed with these naiveties - they're even calling them a "quintessence of physics", because these are the things that they can see and understand...


The lack of introspection and responsibility is what I'm missing there. This way of research is playful and fun, but every entertainment comes at its less or more hidden price, which we all could pay soon. Under the situation, when one half of people is dying from hunger and starvation because of lack of relevant research I even tend to perceive such entertainment amoral.
3.3 / 5 (3) Oct 24, 2010
The problem is that capitalism fails as an incentive for scientists. If our system properly rewarded scientists for their discoveries, people would want to be in the big dollar research where their discoveries will impact the most (and therefor earn the most). As it is most researchers get taken advantage of by their corporate sponsors or the government, who takes their academic work and gives it away at pennies to the dollar to corporations so they can profit. We need legal protection for scientists, all scientists should own the product of their labor!
1 / 5 (13) Oct 24, 2010
all scientists should own the product of their labor
This is equivalent of the requirement, employee should own the product of their labor. A sorta communism, I'm afraid.

Whereas the problem is somewhere else: the physicists are refuting to work on the topics, which don't play well with their existing theories and they tend to research topics, which are supporting them. The Wired article demonstrates it well for the case of cold fusion research:


It's basically the same selfreinforcing mechanism, like this one disputed here:

Every large community postulates its own rules, which are enabling it to grow faster despite the rest of society. The laws developed politicians are primarily protecting the government, the principles of scientific work and grant system are following the interests of scientists, not the rest of society.
1 / 5 (13) Oct 24, 2010
This problem was revealed already in this article: scientists tend to publish positive, rather then negative articles (these denying existing theories the less)


As the result, scientists tend to publish unoriginal research (with many references to earlier work), rather then new, potentially controversial research (with few references to earlier work).


Why they're doing so? Because they're payed for references, not for the originality of research.
not rated yet Oct 24, 2010
The purpous of this article is to see if anyone is actually paying attention!
It's a geek magnet!
5 / 5 (1) Oct 26, 2010
I do believe that an employee should own the product of their labor. Nor should they be employed. Their employer should have to buy that product at normal market value. Thats is capitalism. Anything else is just feudalism in disguise. Communism is everyone owning the product of societies collective labor. Completely different, as you can surely see TDK.
not rated yet Oct 26, 2010
This is equivalent of the requirement, employee should own the product of their labor. A sorta communism, I'm afraid.
I can't believe you're saying that property rights are a form of communism. Even Marjon doesn't screw this up.

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