Why Does Toilet Water Move When It's Windy Outside?

Reader Erin from Baltimore wrote in wondering why the water in her toilet bowl moves on windy days. This is one of those questions – like the one Jason asked about his dog’s popcorn-scented paws – that makes me pause and wonder if I’m getting trolled, or if I’m missing out on a strange phenomena that everyone else seems to be aware of.

So, I did a little Googling and even hung out in the bathroom staring at the toilet bowl one morning (yes, folks, this is the exciting life of a science writer). Turns out Erin isn’t messing with me. Perhaps I'm one of the last people on Earth to realize toilet water moves with the breeze. Way to go, Soniak.

So, what causes this commotion in the latrine?

In many homes (at least in the U.S.), part of the plumbing system is a pipe that runs up and out to the roof. This outlet, called a “vent stack,” allows sewage gases to vent outside instead of through the toilet, sink or tub—which would make the house reek. The stack also allows air to move through the pipes, which makes wastewater drain smoothly and keeps obnoxious gurgling to a minimum.

When the wind blows over the vent stack outlet on the roof, the air pressure in the pipe is lowered. This is Bernoulli’s principle (“as the speed of a moving fluid increases, the pressure within the fluid decreases”), the same thing that gives airplanes their lift, in action in your bathroom. The lowered pressure in the pipes creates a slight suction effect throughout the plumbing system, pulling on water in the toilet below. As the wind kicks up and dies down, the suction gets stronger and weaker, and the water in the bowl sloshes around accordingly.

The Queen of Code: Remembering Grace Hopper
By Lynn Gilbert, CC BY-SA 4.0, Wikimedia Commons

Grace Hopper was a computing pioneer. She coined the term "computer bug" after finding a moth stuck inside Harvard's Mark II computer in 1947 (which in turn led to the term "debug," meaning solving problems in computer code). She did the foundational work that led to the COBOL programming language, used in mission-critical computing systems for decades (including today). She worked in World War II using very early computers to help end the war. When she retired from the U.S. Navy at age 79, she was the oldest active-duty commissioned officer in the service. Hopper, who was born on this day in 1906, is a hero of computing and a brilliant role model, but not many people know her story.

In this short documentary from FiveThirtyEight, directed by Gillian Jacobs, we learned about Grace Hopper from several biographers, archival photographs, and footage of her speaking in her later years. If you've never heard of Grace Hopper, or you're even vaguely interested in the history of computing or women in computing, this is a must-watch:

Why Are Glaciers Blue?

The bright azure blue sported by many glaciers is one of nature's most stunning hues. But how does it happen, when the snow we see is usually white? As Joe Hanson of It's Okay to Be Smart explains in the video below, the snow and ice we see mostly looks white, cloudy, or clear because all of the visible light striking its surface is reflected back to us. But glaciers have a totally different structure—their many layers of tightly compressed snow means light has to travel much further, and is scattered many times throughout the depths. As the light bounces around, the light at the red and yellow end of the spectrum gets absorbed thanks to the vibrations of the water molecules inside the ice, leaving only blue and green light behind. For the details of exactly why that happens, check out Hanson's trip to Alaska's beautiful (and endangered) Mendenhall Glacier below.

[h/t The Kid Should See This]


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