Why Does the Shower Curtain Billow in on Me?

Colorful shower curtain — It looks so innocent – and yet. Fotosearch/Getty Images/Fotosearch RF

You're in the shower, having a delightful time. You have the three S's to make bath time fun: soap, shampoo and Taylor Swift. (She's not there. You're just belting out "Fifteen.")

Even without Taylor, it's hard to be in a bad mood in the shower. It's a magical waterfall land! A tropical destination mere steps from your DVR, with all those episodes of "Nashville"! Your hair will look like Connie Britton's real soon, you tell yourself, as you condition dreamily.

Then a horrible shower monster reaches out and grabs you with its clammy hands and wraps your body in its slimy, sweaty arms. Suddenly, you're Janet Leigh, fighting against the psycho that is your shower curtain.

As you wrestle with the sticky demon, you plead to a higher science power: "Why must our shower curtains attack us?"

First of all, you're right. Unlike the feeling that the other lanes are always moving faster in traffic, you're not making this one up. Your shower curtain is in fact billowing in on you, in an almost predatory way. Folks (more specifically: folks on the internet) have even dubbed it the shower curtain effect.

But why does it happen? Is the shower curtain acting under a natural law? Does the plastic lining have a strong desire for the touch of human skin? Does the curtain billow backward in the Southern Hemisphere?

Peel that plastic away from your flesh and read on for more than you ever wanted to know about your shower curtain's grasp.

Shower to the People

Some might find it silly to study the shower curtain in such depth. Know this: The shower curtain effect is so pronounced a phenomenon that it did finally have to be put to scientific study due to controversial and contradictory theories.

Disclosure: All of that is an exaggeration. But the shower curtain effect did have some advocates with disparate theories, and one man finally had enough free time to tackle the subject with a computer model.

But before we get to the actual cause, let's talk about the two most popular hypotheses for the shower curtain effect.

The Bernoulli principle says that as fluid speeds up, pressure drops. This creates an imbalance of air pressure: The air from the outside remains at the same pressure, pushing in on the lower-pressure air where you're showering, leading the shower curtain to have its way with you.
The buoyancy theory: Hot water from the shower produces hot air. That hot air is less dense, so the colder, denser air from the other side heads for the lower-pressure area, causing the curtain to move inward.

Although they both would make great titles for the "Bourne Identity" franchise, they are both wrong. For one, the Bernoulli principle doesn't address the kind of droplets we'd find in a shower. The buoyancy theory sounds great -- until you realize that the curtain billows in on a cold shower, as well.

This is where our hero comes into the story. An assistant professor of mechanical and industrial engineering at the University of Massachusetts Amherst in 2001, David Schmidt stood up to the Bernoulli and buoyancy bullies. Schmidt created a model for the bathtub and ran a simulation for two weeks that recreated 30 seconds of shower time.

The second-most famous "eureka" moment to come out of a bathtub occurred when Schmidt saw that as the droplets decelerate, they transfer energy to the air around the bathtub, creating a swirling, twirling sideways vortex. The axis of the vortex is perpendicular to the curtain, and its center is a low-pressure region, so the curtain is pulled toward the eye of the hurricane, if you will [source: Schmidt].

Lots More Information

Author's Note: Why does the shower curtain billow in on me?

Explanations aside, we need solutions to our grabby shower partner. Luckily, only the flimsiest of curtains will be affected by the vortex since the forces at play are really weak. So either get a heavier liner or weigh your feeble one down, and you'll be free to sing your duet with Taylor undisturbed

Sources

Adams, Cecil. "Why does the shower curtain blow in despite the water pushing it out (revisited)?" The Straight Dope. August 10, 2001. (May 20, 2001) http://www.straightdope.com/columns/read/1369/why-does-the-shower-curtain-blow-in-despite-the-water-pushing-it-out-revisited
Nave, R. "Bernoulli Equation." Georgia State University. 2014. (May 20, 2014) http://hyperphysics.phy-astr.gsu.edu/hbase/pber.html
Palca, Joe. "Arggh, why does the shower curtain attack me?" National Public Radio. Nov. 4, 2006. (May 20, 2014) http://www.npr.org/templates/story/story.php?storyId=6430581
Ramirez, Anthony. "Ideas and Trends." The New York Times. July 15, 2001. (May 20, 2014) http://www.nytimes.com/2001/07/15/weekinreview/ideas-trends-curtains-how-to-avoid-being-attacked-in-the-shower.html
Schmidt, David. "Why does the shower curtain move toward the water?" Scientific American. July 1, 2001. (May 20, 2014) http://www.scientificamerican.com/article/why-does-the-shower-curta/