I am a professor at the University of Massachusetts-Amherst. I thought I should bring this to your attention. I think I have settled the shower curtain question decisively. –Professor David Schmidt
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Initially I was reluctant to tackle the problem with so many other world crises clamoring for my attention. But eventually I allowed that the phenomenon could be attributed to the Bernoulli effect, the well-known principle that explains how airplanes fly: as the velocity of a fluid increases, its lateral pressure decreases. The water flowing out of the shower nozzle entrains the surrounding air, and the resulting decrease of pressure perpendicular to the direction of flow (following this, are we?) pulls the shower curtain in. I don’t claim this answer represented any bold leap; it was one of two prevailing theories at the time. Predictably, I soon heard from adherents to the other, known as the chimney effect. They argued that air heated by the hot shower water rose and pulled cool air in from below, taking the curtain with it–convection, in other words. As proof, they advised running a cold shower, apparently believing that the curtain would remain motionless. I did as suggested. The shower curtain still blew up and in, though not quite as vigorously. OK, geniuses–you were saying?
At this point I consulted Jearl Walker, who, sad to say, muddied the waters. Jearl, a physicist who then authored the Amateur Scientist column in Scientific American, attributed shower curtain motion to the Coanda effect, the tendency of a fluid in motion to adhere to a surface or, in this case, the tendency of a surface (the curtain) to adhere to a fluid in motion (the flowing water). A bit of a reach, we may agree in retrospect, but when you’ve got a guy like Jearl, who plunged his hand into a pot of molten lead on the Johnny Carson show to demonstrate the Leidenfrost effect, you tend to believe what he says. Anyway, there the matter rested for lo these many years.
