Why Does the Shower Curtain Always Try to Get Me?

For those of you who take baths or are simply unconcerned with hygiene, let me explain the horror that is the “shower curtain effect.” You get in a nice hot shower first thing in the morning. You’re barely awake, but the womb-like confines offer the perfect space to transition from sleepy cretin to functioning human. Until, of course, the shower curtain – who you thought was your friend, who you thought you could trust – gives in to its strange, powerful attraction to running water and billows in towards you. On a good day, it’s a minor annoyance. On a bad day, it’s an unspeakable horror and the curtain actually, like, touches you. And it’s cold. And maybe even a little slimy.

Why does the curtain do this to us? Great minds have been struggling with the problem for years, but until recently all anyone offered were hypotheses. Nobody ever actually tested these explanations and made the results public until a few years ago. That experiment gave us a pretty solid answer, but the theoretical work that came before it is pretty interesting, too. Let’s explore the small handful of different answers that have been suggested over time.

The Bernoulli Principle Hypothesis
We talked about the Bernoulli’s principle the last time I wrote about bathroom science. It states, basically, that an increase in velocity of a fluid (liquid or gas) results in a decrease in pressure around it. With shower curtains, the principle was thought to come into play like this: The water coming out of the shower head causes the air in the shower to start flowing in the same direction that it's traveling, which is parallel to the curtain. The air moving across the inside of the shower curtain causes the air pressure to drop, and the difference in pressure between the two sides of the curtain causes it to move in toward the lower-pressure area. For most of the time that people have been talking about the shower curtain effect scientifically, this has been the leading explanation.

The Buoyancy Hypothesis
Warm air rises up and out of the shower. The air density in the shower is reduced and, like in the Bernoulli hypothesis, the difference in pressure between the shower and outside of the curtain makes the curtain move inward. The big problem with this hypothesis? The curtain still moves in even if you run an ice cold shower.

The Coand? Effect Hypothesis
Jearl Walker, a professor of physics at Cleveland State University who used to write Scientific American’s “Amateur Scientist” column, suggested that the Coand? effect, the tendency of a fluid in motion to adhere to a surface or vice versa, was at work.
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Now, these hypotheses are all well and good. They’re plausible explanations. One was even suggested by a guy who knows a thing or two about physics (and has put his hand in molten lava and poured liquid nitrogen in his mouth to demonstrate its principles). But they don’t mean much without data to back them up.

In 2001, David Schmidt, from the University of Massachusetts, put his own hypothesis to the test and gave us the first evidence-backed explanation to every showerer’s pet peeve.

The Horizontal Vortex Hypothesis
Using a computer model of a shower, Schmidt found that the shower head’s spray creates a horizontal vortex with a low-pressure area center that sucks in the shower curtain. We’ll let Schmidt, who won the 2001 Ig Nobel Prize in Physics for his work, explain his study and its results a little more. As he explained it to Scientific American:

To do the calculation, I drafted a model of a typical shower and divided the shower area into 50,000 minuscule cells. The tub, the showerhead, the curtain rod and the room outside of the shower were all included. I ran [the modeling software] for two weeks on my home computer in the evening and on weekends (when my wife wasn't using the computer). The simulation [which ran some 1.5 trillion calculations] revealed 30 seconds of actual shower time.

When the simulation was complete, it showed that the spray drove a vortex. The center of this vortex, much like the center of a cyclone, is a low-pressure region. This low-pressure region is what pulls the shower curtain in… It is a bit like a sideways dust devil. But unlike a dust devil, this vortex doesn't die out because it is driven continuously by the shower.

NOAA, Wikimedia Commons // Public Domain
Watch the First-Ever Footage of a Baby Dumbo Octopus
NOAA, Wikimedia Commons // Public Domain
NOAA, Wikimedia Commons // Public Domain

Dumbo octopuses are named for the elephant-ear-like fins they use to navigate the deep sea, but until recently, when and how they developed those floppy appendages were a mystery. Now, for the first time, researchers have caught a newborn Dumbo octopus on tape. As reported in the journal Current Biology, they discovered that the creatures are equipped with the fins from the moment they hatch.

Study co-author Tim Shank, a researcher at the Woods Hole Oceanographic Institution in Massachusetts, spotted the octopus in 2005. During a research expedition in the North Atlantic, one of the remotely operated vehicles he was working with collected several coral branches with something strange attached to them. It looked like a bunch of sandy-colored golf balls at first, but then he realized it was an egg sac.

He and his fellow researchers eventually classified the hatchling that emerged as a member of the genus Grimpoteuthis. In other words, it was a Dumbo octopus, though they couldn't determine the exact species. But you wouldn't need a biology degree to spot its resemblance to Disney's famous elephant, as you can see in the video below.

The octopus hatched with a set of functional fins that allowed it to swim around and hunt right away, and an MRI scan revealed fully-developed internal organs and a complex nervous system. As the researchers wrote in their study, Dumbo octopuses enter the world as "competent juveniles" ready to jump straight into adult life.

Grimpoteuthis spends its life in the deep ocean, which makes it difficult to study. Scientists hope the newly-reported findings will make it easier to identify Grimpoteuthis eggs and hatchlings for future research.

Penn Vet Working Dog Center
Stones, Bones, and Wrecks
New Program Trains Dogs to Sniff Out Art Smugglers
Penn Vet Working Dog Center
Penn Vet Working Dog Center

Soon, the dogs you see sniffing out contraband at airports may not be searching for drugs or smuggled Spanish ham. They might be looking for stolen treasures.

K-9 Artifact Finders, a new collaboration between New Hampshire-based cultural heritage law firm Red Arch and the University of Pennsylvania, is training dogs to root out stolen antiquities looted from archaeological sites and museums. The dogs would be stopping them at borders before the items can be sold elsewhere on the black market.

The illegal antiquities trade nets more than $3 billion per year around the world, and trafficking hits countries dealing with ongoing conflict, like Syria and Iraq today, particularly hard. By one estimate, around half a million artifacts were stolen from museums and archaeological sites throughout Iraq between 2003 and 2005 alone. (Famously, the craft-supply chain Hobby Lobby was fined $3 million in 2017 for buying thousands of ancient artifacts looted from Iraq.) In Syria, the Islamic State has been known to loot and sell ancient artifacts including statues, jewelry, and art to fund its operations.

But the problem spans across the world. Between 2007 and 2016, U.S. Customs and Border Control discovered more than 7800 cultural artifacts in the U.S. looted from 30 different countries.

A yellow Lab sniffs a metal cage designed to train dogs on scent detection.
Penn Vet Working Dog Center

K-9 Artifact Finders is the brainchild of Rick St. Hilaire, the executive director of Red Arch. His non-profit firm researches cultural heritage property law and preservation policy, including studying archaeological site looting and antiquities trafficking. Back in 2015, St. Hilaire was reading an article about a working dog trained to sniff out electronics that was able to find USB drives, SD cards, and other data storage devices. He wondered, if dogs could be trained to identify the scents of inorganic materials that make up electronics, could they be trained to sniff out ancient pottery?

To find out, St. Hilaire tells Mental Floss, he contacted the Penn Vet Working Dog Center, a research and training center for detection dogs. In December 2017, Red Arch, the Working Dog Center, and the Penn Museum (which is providing the artifacts to train the dogs) launched K-9 Artifact Finders, and in late January 2018, the five dogs selected for the project began their training, starting with learning the distinct smell of ancient pottery.

“Our theory is, it is a porous material that’s going to have a lot more odor than, say, a metal,” says Cindy Otto, the executive director of the Penn Vet Working Dog Center and the project’s principal investigator.

As you might imagine, museum curators may not be keen on exposing fragile ancient materials to four Labrador retrievers and a German shepherd, and the Working Dog Center didn’t want to take any risks with the Penn Museum’s priceless artifacts. So instead of letting the dogs have free rein to sniff the materials themselves, the project is using cotton balls. The researchers seal the artifacts (broken shards of Syrian pottery) in airtight bags with a cotton ball for 72 hours, then ask the dogs to find the cotton balls in the lab. They’re being trained to disregard the smell of the cotton ball itself, the smell of the bag it was stored in, and ideally, the smell of modern-day pottery, eventually being able to zero in on the smell that distinguishes ancient pottery specifically.

A dog looks out over the metal "pinhweel" training mechanism.
Penn Vet Working Dog Center

“The dogs are responding well,” Otto tells Mental Floss, explaining that the training program is at the stage of "exposing them to the odor and having them recognize it.”

The dogs involved in the project were chosen for their calm-but-curious demeanors and sensitive noses (one also works as a drug-detection dog when she’s not training on pottery). They had to be motivated enough to want to hunt down the cotton balls, but not aggressive or easily distracted.

Right now, the dogs train three days a week, and will continue to work on their pottery-detection skills for the first stage of the project, which the researchers expect will last for the next nine months. Depending on how the first phase of the training goes, the researchers hope to be able to then take the dogs out into the field to see if they can find the odor of ancient pottery in real-life situations, like in suitcases, rather than in a laboratory setting. Eventually, they also hope to train the dogs on other types of objects, and perhaps even pinpoint the chemical signatures that make artifacts smell distinct.

Pottery-sniffing dogs won’t be showing up at airport customs or on shipping docks soon, but one day, they could be as common as drug-sniffing canines. If dogs can detect low blood sugar or find a tiny USB drive hidden in a house, surely they can figure out if you’re smuggling a sculpture made thousands of years ago in your suitcase.


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