# How fast to shake to get dry? Science answers…

By Aimee Whitcroft 21/10/2010

It’s a difficult subject, this.

And probably too punworthy for me to be able to help myself (although I shall try).

Some enterprising scientists have discovered the optimal oscillation needed by a hairy beastie shaking itself dry.  And by oscillation, of course, I mean ‘shaking of the body’. Or, possibly, ‘booty’.

They filmed a bunch of dogs shaking themselves as a means of water dispersal*, and had  a look at the results, which for labrador retrievers was 4.3 Hz.

This led to a lovely model in which they hypothesized that the oscillation necessary is R^0.5, where R is the radius of the body**. Which means that smaller animals will have to shake faster.  A mouse must shake faster than, say, a woolly mammoth.

Of course, and as with all science, the prediction above needs to be tested, and this is what our friendly scientists did.  They looked at mice, cats, bears, and no doubt a plethora of other beasties, and found that yes, the larger the animal, the lower the Hz.

To be more specific, mice come in at 27 Hz, cats at 6Hz, and bears at a stunning 4 Hz.  (I still want to see a woolly mammoth shaking, for the humour/awe as well as the science)

They also found that the equation is a little different from that originally conceived, with the optimal oscillation being closer to R^0.75 = driest beastie possible.

Thought points:

How exactly does one define R?  Does it include or exclude fur?

To what practical use could we put this?  A device to optimally oscillate string mops?  How fast one should shake one’s head to dry our hair?  (Or, for that matter, how best to head bang to ensure maximum sweat coverage of those around one?)

Perhaps there’s a use for salad spinners?

And see?  I managed not to pun too much (she said drily)

UPDATE:

I clearly like things to do with fluid dynamics, given that I’ve also posted about teapots

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*One wonders if they also measured the oscillation frequency necessary to make any humans in the vicinity scream the loudest.

** Reasoning as follows, for those who’re interested.  Water is stuck to the animal’s fur due to surface tension between water and air.  In order for the water to become unstuck, enough centripetal force*** needs to be generated to overcome this.

*** Yes yes, I know.

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The arXiv article I based this on.  As usual, the authors of these articles are legendary in their ability to explain this sort of stuff.  Note their wonderfully facepalm-worthy use of ‘paws.

### 0 Responses to “How fast to shake to get dry? Science answers…”

• Alison Campbell says:

Excellent! So that’s why Ben (a miniature poodle) shakes himself so hard his ears rattle, while my dear departed Bella (a lab) did more of a leisurely skin shuffle!

• Aimee Whitcroft says:

I’m also wondering whether there’s some inherent tie between size of dog, oscillation frequency, and neuroticism…

• Aimee Whitcroft says:

In other news:
How on earth do furries _know_ what the optimal oscillation is?

What if the scientists have been looking at the ones that are lazier/more energetic than is representative? Even if they are representative, how do we know it’s the optimal frequency?

Can haz more experimentz?

• miked says:

The ONLY reason for a salad spinner is so I can justify buying esoteric power tools.

• […] Other times I’ve mentioned arXiv include articles on the teapot effect, shaking oneself dry, modelling cow behaviour, time, and science […]

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