Universal Law of Urination: 21 Seconds

    October 24, 2013

Researchers at the Georgia Institute of Technology have established the standard for a “law of urination,” which states that all mammals take roughly 21 seconds to pee. Big mammals, small mammals, boy animals, girl animals – anything weighing over 1 kilogram takes 21 seconds to tinkle, give or take 13 seconds.

During a trip to Zoo Atlanta, Patricia Yang, a biologist at Georgia Tech, along with her colleagues, gauged the duration of urination from several different types of animals, with bladders ranging in capacity from less than 4 ounces to more than 25 gallons. To help reinforce the new findings, here’s a scientific reel, produced by Georgia Tech, of a bunch of peeing animals for your Thursday:

But why is this peeing time so universal? According to the research, the “feat is made possible by the increasing urethra length of large animals which amplifies gravitational force and flow rate. We also demonstrate the challenges faced by the urinary system for rodents and other small mammals for which urine flow is limited to single drops. Our findings reveal the urethra evolved as a flow-enhancing device, enabling the urinary system to be scaled up without compromising its function. This study may help in the diagnosis of urinary problems in animals and in inspiring the design of scalable hydrodynamic systems based on those in nature.”

“Most of the research is on humans or animals smaller than humans,” Yang said, (The 21 seconds applies to humans too), adding that gravitational forces don’t come much into play regarding smaller mammals. Though when it comes to something like an elephant, which has a 3-foot-long urethra as thick as a household PVC pipe, the pee has time to reach a higher velocity. Essentially, since an elephant’s 25 gallons of pee gets moving at a much higher rate, it can approximate the speed of a mouse.

The team plans to submit their findings next month at the American Physical Society Division of Fluid Dynamics meeting in Pittsburgh, Pennsylvania. Yang hopes the law of urination might even influence new designs for water towers, which also pump water using the force of gravity.

Image via Wikimedia Commons.