Ever wonder why shower curtains blow inward when taking a nice hot shower? So do scientists. Many have tried to figure out how and why this happens, but no one has ever proven their theories conclusively. Who would have thought that the simple mechanics of a shower curtain blowing inwards would stump so many scientists?

Multiple Theories

There are currently 4 theories which attempt to explain how the shower curtain effect works. The first is called the Buoyancy theory. The buoyancy theory says that as the hot air rises, and replaces the cold air, it creates a Coandă effect which is similar to a small vortex (or tornado) of air which sucks the curtain inwards.

The second is the Bernoulli effect. This states that the air matches the velocity of the water coming out of the shower-head and lowers the air pressure inside the shower and against the inside of the shower curtain. This results in the shower curtain being pulled inward. This effect can be seen every time you fly in a plane. It’s what occurs on an aircraft’s wings which give it lift.

The third is a combination of the first two. It’s called the Horizontal vortex theory. A computer model showed that the water coming out of the shower-head can create a horizontal vortex (sideways tornado) which causes a pressure drop and pulls in the shower curtain.

The fourth and final explanation is simple condensation. A hot shower produces steam that will condenses on the shower side of the curtain and lowering the pressure there. The condensation will be continually replaced causing a temperature fluctuation which results in times where net steam production is negative.

So there you have it. Who would have thought such a simple thing still remains partially unproven and under contention.

Bonus fact: David Schmidt of University of Massachusetts was awarded the 2001 Ig Nobel Prize in Physics for his partial solution (horizontal vortex theory) to the question of why shower curtains billow inwards. The Ig Nobel Prize is more for fun than prestige, but it honors those who first make people laugh, then make them think. The organization (made up of actual Nobel laureates) exist to celebrate the unusual and imaginative. That sounds like it’s right up our alley.

References:

Experimental Investigation of the Influence of the Relative Position of the Scattering Layer on Image Quality: the Shower Curtain Effect

NPR: Why does the shower curtain attack me?