Friday, October 07, 2005

Penguin Poo Projection

The Ig Nobel prize for Fluid Dynamics was awarded yesterday to Victor B. Meyer-Rochow and Jozsef Gal for their 2003 paper on Pressures produced when penguins pooh - calculations on avian defecation. This three page paper was published in the journal Polar Biology as a short note.

picture from penguin pooh paperPicture from VBM-R & JG's penguin pooh paper

Suppose you have a penguin. Specifically, an Adelie or Chinstrap penguin. Penguins, like other higher vertebrates, do doo-doo. However, they are not turd-makers, i.e. don't drop shit. Instead, they shoot it about 40cm. (Why they do so is unclear - the authors suggest that this is to avoid "soil[ing] their plumage".)

Penguin shit is a semi-liquid/solid goo whose viscosity is -- by assumption of the authors -- about that of olive oil. You can think of viscosity as `resistance to flow' -- ketchup is far more viscous than water, for instance. If

  1. penguin shit is like water i.e. not viscous,
  2. a penguin's asshole is horizontal while firing (see picture above), and
  3. the shitting is instantaneous (it actually takes about half a second)

then the pressure required to shoot it 40cm across the ground, from a height of 20cm, is around 34 mmHg or 4600 Pascals, about a third of human blood pressure.

The authors use the Instantaneous Shitting Assumption to avoid having to know the shape of the penguin's rear nozzle while firing. Having said that, they manage to cite a paper from 1883; they make use of the observation by one of the scientists on the Challenger Expedition that a penguin's cloaca (a fancy word for assholes in birds). It is normally a horizontal slit. But before you start thinking of how a possibly short-sighted cameraless 19th century ornithologist might determine this, bear in mind that they also cite a 1981 book chapter devoted to cloaca.

As mentioned earlier, fresh penguin guano is more viscous, i.e. flows less freely than, water. When this is taken into consideration, the pressure required is over twice as much. Under certain conditions it can even be as much as 60 000 Pascals.

The authors finally note that further trips to Antarctica are required to determine if penguins take into account wind direction while firing, as shitting into the wind would presumably be sub-optimal.


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