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Everybody Pees, and Most Mammals Pee in the Same Amount of Time

Science: Answering the questions you never thought to ask.

Lamb

Mammals range in size, and so do their bladders. A great dane can hold about 0.4 gallons of urine, while an elephant can store 42 gallons. You might think that means it takes an elephant longer to pee and empty its bladder, but you’d be wrong. Regardless of size, mammals take nearly the same amount of time to pee. That’s a thing we know now.

This discovery came from mechanical engineer David Hu at the Georgia Institute of Technology. Hu is also a new father, and after changing a bunch of wet diapers (know that feel, bro) he became curious about the physics of urination. We think that’s something our regular readers can relate to.

Hu took to figuring out how different animals pee by observing them at Zoo Atlanta with a team of three graduate students. They recorded the animals urinating with high speed cameras, and also watched YouTube videos of animals as additional research.

So how long does it take? If you’re a mammal weighing more than 2.2 lbs (and we’re pretty sure you are) it should take you about 20 seconds to empty a full bladder. That’s regardless of how many gallons you’re expelling, which comes down to urethra width. The larger animals had wider urethras, allowing them to expel more fluid in the same time as a much smaller animal.

The timing isn’t exactly the same, but it seems that 20 seconds is the golden (sorry, couldn’t help it) number. A great dane takes 24 seconds, while an African elephant takes only 22. Remember, that’s 42 gallons of elephant pee, meaning the animal is letting out nearly two gallons per second.

If you’re wondering why this rule doesn’t apply to smaller animals under 2.2 lbs, it’s because their urethras are so small that the surface tension of the liquid urine becomes a factor.

Now we all know a little bit more about how animals pee. Thanks, Mr. Hu.

(via National Geographic, image via Tobias on Flickr)

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