The Ones and Twos of Going Number 1 and Number 2

Amount of time for an animal to poop

Did you ever complain while doing your math homework and ask, “Why do I need to learn this?” Probably someone responded by telling you that no matter what you choose to do with your life, you’re going to have to use math in some way.

It turns out this is true, even if you plan to spend your life cleaning up after animals. Scientists have applied their finely-tuned brains to unlock the mysteries of what happens on the other end of an animal’s body. To put it a bit more bluntly, thanks to a bit of math, we now know just how long it takes for animals to poop and pee.

In 2015, Patricia Yang, David Hu, Jonathan Pham, and Jerome Choo, were awarded the Ig Nobel Prize when they concluded that nearly all mammals empty their bladders in about 21 seconds (plus or minus 13 seconds).

Their study (click here to read), “Duration of Urination Does Not Change With Body Size,” was published in the Proceedings of the National Academy of Sciences. The researchers used high-speed videography and flow-rate measurement during their research at Zoo Atlanta. They concluded that all mammals above 3 kg (6.6 lbs) in weight empty their bladders over a nearly constant duration. This holds true for the common house cat all the way to the blue whale. This feat is possible, because larger animals have longer urethras and thus, higher gravitational force and higher flow speed.

Being #1 in their field did not stop the researchers from turning their attention to #2. They have now unlocked the mysteries of how long it takes animals to empty their bowels, as well.

Chart showing the duration of a bowel movement, compared to the mass of the animal. (Click on image to expand)

The Georgia Tech scientific team published “Hydrodynamics of Defecation” in the journal Soft Matter. (Editor’s Note: We were excited to learn that such a journal exists, hoping it was entirely devoted to the study of pooping. This would have produced a goldmine of article ideas for Commonplace Fun Facts. Alas, it is not nearly as exciting as we had hoped. Soft Matter is, according to its website, “an interdisciplinary journal focusing on innovative soft matter topics through original research and reviews.”)

The study (click here to read) To reach their conclusions, the scientists rolled up their sleeves (and presumably put on rubber gloves and face masks) and started measuring a whole bunch of poop. They limited their studies to “steady state” pooping. In other words, they looked only at animals that defecate with cylindrical feces, such as humans. This excluded creatures such as rabbits that produce little pellets. This leaves open a whole area of study for any of you who are stumped about how you will find purpose for your life.

All animals poop at the same speed: 12 seconds, to be precise.

After studying a bunch of animals in person, as well as viewing a bunch of YouTube videos, the scientists were surprised to learn that the size of an animal barely factors into the amount of time it takes to lighten its load. They note, “As body mass increases by a factor of ten billion, defecation time decreases by only a factor of ten. This invariance in defecation time is surprising even though the rectum of an elephant of 40 cm in length is nearly ten times as long as that of a cat.”

In other words, no matter what size animal, (or person, for that matter), the amount of time it takes for a piece of poo to clear the rectum is pretty much 12 seconds for everyone. It seems that defecating is the great equalizer of nature.

If you take the time to read through the 11-page study, you will be charmed by several full-color pictures of the droppings of several species. You can also meditate upon the still shots from several YouTube videos, zeroing in on the least-flattering part of a number of animals and capturing the moment their poo first sees the light of day.

More importantly, the study presents no small number of handy mathematical equations. Imagine how impressed your friends will be when you can tell them that the defecation time of an animal (or person, for that matter), is determined by the ratio of the fecal length to the fecal velocity:

Defecation rate equation

Contained with the pages of the study is the conclusion that the size of a piece of poop is determined by the length of the rectum. This is not nearly as important as the amount of mucus in the mix. It is the mucus that causes quick and easy passage into the light of daylight. Too much or too little mucus can make a regular day quite irregular. That’s why the study also includes a couple of handy equations for you to contemplate while staking a claim to the most convenient commode:

EDITOR’S NOTE: The juvenile-minded staff of the Commonplace Fun Facts writing team insisted upon inserting a joke at this point about the constipated mathematician who worked it out with a pencil. Thankfully, those with more maturity and savoir-faire prevailed, and the reader is spared such puerile buffoonery.

These equations led the researchers to conclude that diarrhea takes the gastrointestinal tract out of the picture, allowing gravity to do most of the work in emptying the bowels. They estimated that a 70 kg (or about 154 lbs) human can get the job done in about half a second. Constipation, on the other hand, assumes a reduction in mucus. With all mucus eliminated and confronted with the “stiffest feces,” even with maximum rectal pressure applied, one can expect a 6-hour transit for one persistent piece of blockage. They also note that intestinal walls can speed things along considerably by deforming the poo, thus making it a wee bit more aerodynamic rectaldynamic.

So there you have it. Whether you’re talking about the cube-shaped droppings of a wombat or trying to figure out how long Nikola Tesla should have kept shaking Mark Twain to help him with his irregularity, you can be #1 among your friends as you expound upon #2.

8 replies »

  1. My father told me the one about the constipated mathematician (only his guy worked it out with a slide rule) when I was seven. That’s still the joke of his that makes me laugh the hardest, and now I’m in my early fifties. I love my dad!!!

    Liked by 1 person

  2. Reblogged this on My Corner and commented:

    Good morning. When you were a kid, you probably wondered why you had to learn math. Well, maybe this post from Common Place Fun Facts will enlighten you. It should definitely give you some food for thought while you’re picking up your pet’s droppings. Enjoy, and have a wonderful Wednesday!

    Liked by 1 person

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