A Profusion of Pressurized Penguin Poo
What variables do you need to consider when you are contemplating penguin poo pressure? First, you need to consider how WIDE the opening of your "gun" is. using "a few 'spot-on' photographs", taken during the event, they estimated the diameter of the cloaca during at about 8mm when the penguin pinches a loaf. You then need to work out height. As the penguin moves up to the edge of its nest to do its business, the cloaca is going to be a bit higher than normal, around 20cm. And then you need to determine the viscosity of your poo, whether its more liquidy or more solid. Once you have all of these and the distance the poo travels, you can calculate the velocity of the dump using this model:
Once you have an idea of velocity, you can start working out pressure for fluids of different viscosities. The authors started out with the "ideal" viscosity of something near water. While they got a pressure of around 34mmHg (not too bad), the low viscosity, and the constant pressure, would result in the poo taking on a parabola. This would be great if the penguin could REALLY get its butt in the air, but since it stands upright and can't...it may be implausible.
However, a higher viscosity works better. If you use a viscosity of say...below glycerine, but above glycol (they tried to take poo samples and measure the viscosity directly, but things like bits of shrimp and fish bones and scales kept getting in the way. The things people will do for science), and you assume that you're working with only initial pressure (to propel the mass away from the nest, but relax immediately after), you get a pressure between 77 and 450 mmHg. This number takes into account friction in the intestintal tract.
That's a lot of pressure. Really. Humans usually poop at around 55mmHg (100 if you're feeling stopped up). So up to 450mmHg is pretty substantial. And it'd be interesting to look at the muscles and see how they do it
(also the authors refer to "non-Newtonian mechanisms of mucus participation", which, whatever it is, is probably both awesome and kind of gross).