The physics of drying off

October 30, 2010 12:37 PM

The Wet-Dog Shake (SLYT). Scientists have worked out the optimum amount of shaking that animals have to do to dry themselves after getting wet. Filming in slow motion, they captured various animals shaking themselves off, from a wet mouse to a big grizzly bear.

Link to news story.

posted by 7-7 (41 comments total)

this is very useful information to know! My father, fairly hairy, shakes himself when he leaves the bathtub, shakes himself, and I have often wondered how his shaking compares to our Golden Retriever.
posted by Postroad at 12:41 PM on October 30, 2010

The cross-section of the dog showing it's radius was inexplicably hilarious.
posted by Nomiconic at 12:42 PM on October 30, 2010 [4 favorites]

You know that scene in Young Frankenstein where Dr. Frankenstein is doing the educational autopsy and his students just pass out one by one? Well, I assume this video is some sort of test to weed out the true scientists from the people who just go ohmygodfuzzyanimalswiggling! At the end of the 2:59, only one of those two groups actually knows what the video was about.

This is how I know I will never be a scientist.
posted by griphus at 12:45 PM on October 30, 2010 [2 favorites]

Ah! This was on CBC's Quirks and Quarks today, too. The show is up on the site now and the podcast is available for download from iTunes, too.
posted by maudlin at 12:50 PM on October 30, 2010

In my house this is known by its colloquial name: "Sadie, noooo! Wait 'till I grab a-----towel."
posted by phunniemee at 12:51 PM on October 30, 2010 [8 favorites]

Next up: the Fibonacci numbers of rug beating.
posted by Burhanistan at 12:51 PM on October 30, 2010 [3 favorites]

Wet cat shake.
posted by maudlin at 12:53 PM on October 30, 2010 [2 favorites]

spoiler: w ~ r^0.75
posted by idiopath at 12:53 PM on October 30, 2010 [2 favorites]

NO! NOT IN THE HOUSE! NOT IN TH-
posted by TheWhiteSkull at 12:56 PM on October 30, 2010 [2 favorites]

I have a Belgian sheepdog whose shaking-off actually violates conservation of mass. Scientists should be looking into that.
posted by Wolfdog at 12:59 PM on October 30, 2010

Mouse, rat, guinea pig, chihuahua, cat, poodle, small husky, chow, large husky, labrador 1, labrador 2, labrador 3, labrador 4, sumatran tiger, giant panda, brown bear, salad spinner.

In nature, ω~R^-0.75, not R^-0.5 as predicted. Is this due to the presence of fur?

Yes, if only our salad spinners had fur, everything would make perfect sense.
posted by Gator at 12:59 PM on October 30, 2010

The original video was one of the submissions to the APS "Gallery of Fluid Motion" competition. You can find it, and many of the others, by looking at October's submission to the physics.flu-dyn ArXiv. (I don't know of a good way to find just the competition submissions, so you'll have to wade through some actual papers, too.)

"The Wet Dog Shake" one is here. You'll want to click on "other formats" to download all the movies (as a gzipped tar archive). You might also enjoy such entries as "The Hungry Fly: Hydrodynamics of feeding in the common house fly," or "Ants as Fluids," or this one on Tibetan singing bowls.
posted by chalkbored at 1:03 PM on October 30, 2010 [1 favorite]

Yes, if only our salad spinners had fur, everything would make perfect sense.

It's only a matter of time.
posted by griphus at 1:10 PM on October 30, 2010 [1 favorite]

I'm surprised that they didn't take into consideration hair properties: density, length, shape (straight, curly etc.), greasiness... They should also study the ladies in shampoo commercials.
posted by elgilito at 1:12 PM on October 30, 2010 [1 favorite]

Fun, useful fact: when Fido gets that look like he's going to shake a few gallons of water onto you/everything, grab his snout. He can't shake unless he starts with his nose. Dogs can't start in the middle.

I'm totally serious, try it.
posted by sidereal at 1:12 PM on October 30, 2010 [12 favorites]

Bad bear.
posted by TheWhiteSkull at 1:14 PM on October 30, 2010 [3 favorites]

I was hoping for Shakin' All Over as a soundtrack.
posted by Tube at 1:17 PM on October 30, 2010

Wrong shampoo commercial, elgilito.
posted by Wolfdog at 1:26 PM on October 30, 2010

I suspected even before clicking that dudes from Georgia Tech were behind this.

lol salad spinner
posted by elizardbits at 1:30 PM on October 30, 2010

Seems like you need a bunch of floppy loose stuff in the very outer layer to make shaking worthwhile; maybe that's where the extra .25 comes from (the effective diameter is larger than the real diameter because it should include the maximum diameter with the floppy stuff pulled out to its maximum extension, or something).
posted by jamjam at 1:33 PM on October 30, 2010

Our little terrier/poodle mix, Cleo, who is very low to the ground, sometimes shakes herself so vigorously that she falls down. It doesn't seem to bother her, she just stands up and resumes shaking. I wonder if there's a mathematical explanation for the falling down part.
posted by amyms at 1:38 PM on October 30, 2010

I thought that, too, jamjam, but his graph with data points seems to indicate the opposite about the effective diameter. It looks like if the radius of the long-haired animals were a little shorter, it would fit his trend line better.

It seems to me, though, he's graphing the wrong parameter. It's only coincidental that animals shake off sinusoidally, which makes frequency related at all. Really what he should graph is peak angular velocity, which is what directly causes the centripetal force. Maybe that's why the bigger animals fall above the curve so far - they physically can't shake as fast as his model would require, but they can still get the required speed up on each shake.
posted by ctmf at 1:52 PM on October 30, 2010

Yikes. For a moment I thought "wet dog shake" was a new beverage...
posted by ZenMasterThis at 1:58 PM on October 30, 2010

The cross-section of the dog showing it's radius was inexplicably hilarious.

I was petting a dog while watching the video, and also found the "dog of radius r" to be hilarious.
posted by Forktine at 2:06 PM on October 30, 2010

they physically can't shake as fast as his model would require, but they can still get the required speed up on each shake.

I think it's like cracking a long bullwhip. The bear starts slow, but the whip snap is quite fast.
posted by Forktine at 2:07 PM on October 30, 2010

My Google-fu is failing me at the moment, but I recall reading an article some time ago about wet dogs shaking off their fur. This particular study showed that stray dogs shook off immediately after getting wet (whether from rain or after swimming), while "pet" dogs would wait to shake until they were near their human, even if it meant traversing many yards from the outdoors while soaking wet to be let inside. The frustrating part of not being able to find the article is that I can't remember what the researchers postulated as a reason for "owned" dogs waiting to shake water onto their owners.
posted by Oriole Adams at 2:45 PM on October 30, 2010

No scientist has ever expressed any interest in filming me shaking myself off. This is probably just as well, all things considered.
posted by Decani at 4:03 PM on October 30, 2010

Nice to see some fluoroscopy. You don't get those so much anymore. When I was little, I thought that all X-Rays were like fluoroscopes, and that you could see the people's skeletons moving around. Then when I got older I found out that x-ray images aren't like that, they're like photographs instead, so I assumed all those Warner Brothers cartoons were just making things up. And then I didn't find out until graduate school that there really is such a device that does moving x-ray images, but we don't use them except at great need, because of all the ionizing radiation.

Also nice to see some good classic "medium scale" physics. Quantum scale and relativistic physics get all the fun these days; I mean sure, whizzing particles around at awesome speeds is sexy, but it's really comforting sometimes to have a bit of hypothesis-prediction-videovideo-mathmathmath-conclusion physics that I can just about get my brain to understand.


omgfuzzyanimalswiggling ssocuuuuute!
posted by Made of Star Stuff at 4:05 PM on October 30, 2010

The Wet-Dog Shake (SLYT)
...
Link to news story

I fear that "SLYT" is slowly becoming something akin to "ATM machine," or something similar to it.
posted by CitrusFreak12 at 4:11 PM on October 30, 2010

Well, the link that had "SLYT" in its text was in fact a link to a YouTube video.

And there was only one of it.
posted by LogicalDash at 4:39 PM on October 30, 2010

So it follows, logically, that pulsars are very densely wet radioactive dogs of various sizes at a very far distances. Oriole Adam's apocryphal research would indicate that the dogs are tame, and moving with intent in our direction. What to do?
posted by eegphalanges at 5:01 PM on October 30, 2010 [1 favorite]

My tangential offering: Vitalic - Poney Part 1 - (2:15)
posted by kitsy at 6:47 PM on October 30, 2010 [2 favorites]

Destined for an IgNobel prize or at least citation by the Annals of Improbable Research. I'm just disappointed that they didn't capture and dunk an actual grizzly bear.
posted by bad grammar at 7:12 PM on October 30, 2010 [1 favorite]

@griphus: You know that scene in Young Frankenstein where Dr. Frankenstein is doing the educational autopsy and his students just pass out one by one?

Nope. But that's because that's from the TV series "Quincy, M.E.", not Young Frankenstein.
posted by hanov3r at 9:15 PM on October 30, 2010

Phew. Now that we got this one sorted, we can move on to curing cancer.
posted by 1000monkeys at 2:11 AM on October 31, 2010 [1 favorite]

If people only studied things that were determined by others to be nontrivial, there wouldn't be enough grant money to go around and everybody would go into accounting instead of medicine. And there wouldn't be anything to read on Metafilter.
posted by Peach at 6:41 AM on October 31, 2010

Nope. But that's because that's from the TV series "Quincy, M.E.", not Young Frankenstein.

It might not be YF, but I definitely saw it somewhere that wasn't Quincy. This is going to bug me to hell now.
posted by griphus at 6:53 AM on October 31, 2010

Ah! Dracula: Dead and Loving It. I knew it had something to do with Mel Brooks.
posted by griphus at 6:57 AM on October 31, 2010

This brings up a related question: why do dry dogs do the shake when invited to go for a walk? Specifically, why does my dog do this?
posted by Wordwoman at 8:35 AM on October 31, 2010

Did you ask him?
posted by Burhanistan at 9:51 AM on October 31, 2010

This is so hilariously asinine.
posted by biochemist at 10:41 AM on October 31, 2010