If you have an ACS member number, please enter it here so we can link this account to your membership. (optional)

ACS values your privacy. By submitting your information, you are gaining access to C&EN and subscribing to our weekly newsletter. We use the information you provide to make your reading experience better, and we will never sell your data to third party members.


K-12 Education


The Law Of Urination, Programmer High Jinks

by Lauren K. Wolf
July 28, 2014 | A version of this story appeared in Volume 92, Issue 30


In recent years, David L. Hu has had a lot of time to contemplate urine. His wife gave birth to two children in rapid succession, and Hu, a fluid dynamics professor at Georgia Tech, was changing loads of diapers.

Credit: David Hu/Georgia Tech
Pee-parazzi: Georgia Tech students film a goat urinating at the Atlanta zoo.
A research team records a goat urinating with a high-speed camera at the Atlanta zoo.
Credit: David Hu/Georgia Tech
Pee-parazzi: Georgia Tech students film a goat urinating at the Atlanta zoo.

For having such small bladders, his kids took an awfully long time to pee, he thought. Would it take even longer if they had huge bladders, like elephants?

Not one to leave a scientific question unanswered, Hu decided to get his research team involved. The scientists traveled to the zoo in Atlanta and began measuring urination speed and volume for a variety of animals. What they found was unexpected. During a single bathroom break, animals ranging from an 11-lb cat to an 18,000-lb elephant took about the same time to urinate: 21 seconds on average (Proc. Natl. Acad. Sci. USA 2014, DOI: 10.1073/pnas.1402289111).

The reason urination time didn’t vary much with bladder size or body weight, the research team found, has to do with gravity and the dimensions of the creatures’ urethras. An elephant’s urethra, the tube that directs pee out of its body, is much longer and wider than a cat’s. When the pachyderm has to go, as gravity’s weight pushes down, the giant animal voids its 18-L bladder at a rapid pace, like a fire hose. The cat’s 5-mL bladder empties at a much slower pace, through its smaller urethra. But both animals’ pee sessions have about the same duration.

Hu and his group—including grad student Patricia J. Yang—derived a mathematical relation they call “the law of urination” to describe the phenomenon. Where the law breaks down is for mammals lighter than about 2 lb, the researchers say. Below this body mass, creatures’ urethras become so narrow that viscous and capillary forces dominate, and the animals’ urine comes out as tiny droplets, rather than as jets. “Animals like rats and mice, they urinate in only half a second,” Hu says. “It’s like trying to push fluid out through a coffee stirrer. And it’s so fast, you need a high-speed camera to capture it.”

A few weeks ago, the Newscripts gang brought you a tale of clandestine video games hidden in a high-performance liquid chromatography (HPLC) instrument’s control panel (C&EN, June 30, page 40). Users found the right sequence of commands to play arcade classics such as Space Invaders while waiting for samples to process.

Instrument displaying text.
Cheeky: Analytical chemistry instruments say the darndest things.

Amused, C&EN reader Ron Sheinson of Silver Spring, Md., wrote in to tell us that programmers have been horsing around for as long as there have been programs to write. “In the early 1970s, our Finnigan mass spectrometer had a couple games on it,” says Sheinson, a 50-year ACS member. One game asked a user to enter a number from one through 10 by using the instrument’s typewriter-style keys. No matter what the person entered, Sheinson recalls, the machine would spit out, “You lose. Take off your clothes.”

Sheinson, who during the ’70s worked on an infrared spectrometer meant to analyze contaminants in liquid oxygen supplies aboard Navy ships, also remembers seeing a comedic machine at an analytical instruments show. “The pressure to unveil instrumentation first was tremendous back then,” he says. Walking among the exhibit stalls, he spotted a rival IR spectrometer that wasn’t quite ready for prime time but was making its debut anyway. When a user pushed a button for analysis, the display popped up, “Not now, I have a headache.”

“Chemists, engineers, and programmers,” Sheinson says wryly, “are a fun bunch in their own ways.”

Lauren Wolf wrote this week’s column. Please send comments and suggestions to


This article has been sent to the following recipient:

Chemistry matters. Join us to get the news you need.