…I’ve been intrigued, and bothered, by this mystery for some time. And I apologize if someone has addressed it with this particular case, but I couldn’t find it in archives. But… I tend to agree with Cecil’s first theory (Bernoulli) as opposed to the Jearl Coanda effect that he backtslid into, at least partly. Let me explain. I’m prone to take insanely hot showers and am frequently acosted by the curtain. For years now I’ve resolved myself to just trust Cecil and this Jearl guy he seems to admire. But then it happened (dramatic pause).
The other day, in one of my insanely hot showers, as I was being acosted, I turned off the water. And guess what? The shower curtain did not return to its original position as one might expect. No! It lingered for 10 seconds after I turned the water off. It even has magnets at the bottom that were no match for the curtains will. So, I’m saying that the curtain lingered until the pressure equalized itself on either side of the curtain.
I agree. This answer of Cecil’s has bothered me more than any other I can think of. The Coanda effect is responsible for airplane wings flying, because the curved top surface of the wing causes the airflow to adhere to it, and the air is thrown downwards as the wing passes. The lift comes from the fact that air is deflected down.
With a shower curtain, are they saying that the curtain deflects air towards outside the shower? This is the only way it could go to cause the Coanda effect to be the explanation, and I can’t think of any way for that to make sense.
I’m convinced that it’s the heat rising. And as soon as I fix the shower knob in the bathroom of mine with a curtain, and buy some cigarettes, I’m going to demonstrate it.
By the way, the questioner’s statement about why airplane wings fly is not entirely correct - he states that “the air travelling over the top of the wing has farther to go, therefore it travels faster, resulting in lower air pressure.” He’s assuming that the air going over the wing and that going under it arrive at the trailing edge at the same time. Trouble is, wind tunnel tests with pulsed smoke clearly show that the air over the top arrives later.
The column (including Slug Signorino’s illustration) can also be found on pages 104-108 of Cecil Adams’ book «More of the Straight Dope».
(edited to fix page number)
This one bugs me every single morning when I shower and is the source of a running argument between Mr. Pug and me, as Mr. Pug favors the “heat rising” hypothesis and I favor the Coanda hypothesis.
CurtC, regarding heat rising: Yes, but as Cecil says and my own experience bears out, even when you run COLD water the curtain still rises, although it doesn’t continue to rise after the water is turned off. Perhaps it rises at first due to the Coanda principle and continues to remain aloft because of residual heat? And if the Bernoulli principle were correct, why would it work on a flat, hanging curtain? It seems to me that curvature, like in an airplane wing, would be necessary for that.
I agree with Cecil. I am certainly a physics dunce, but Cecil’s deduction was so logical that I feel the issue was solved. By the way, thanks, Cecil, for presenting a problem that still makes my brain hurt every morning as I shower. Or was that last night’s red wine . . .?
Because he wants to? Maybe he enjoys sharing science information with the general lay public. Maybe he enjoys writing.
Check out http://www.badastronomy.com . It is a website put together and run by an astronomer who works on Hubble data. He’s a professional astronomer, full time scientist, who happens to want to share his amateur enjoyment of astronomy as well, and educate the public. So he runs his own web site, and gives publicity tours, and has been interviewed several times on national news. Because of his hobby, not because of his profession.
It’s a column for amateur scientists, not by an amateur scientist.
(I know, it wasn’t the actual point of the OP, but…)
The solution to this shower-curtain-billowing-out-and-attacking-you problem is to get a heavy-duty plastic shower curtain!
I’ve forgotten the thickness in mils, but they’re usually labeled “heavy duty” and weigh maybe 3-4 times what the typical one weighs.
I’ve had two – the first one lasted at least 8 years. So, in consumer terms, they last “forever”. And I got them at the local mega-discount-department-store (you-know-who-I-mean).
And – here’s the key point – they’re so heavy that the billowing is hardly noticeable!
Problem solved (if you don’t like being wrapped up in your shower curtain).
And in a pinch if you have to containerize a pissed off cat wet with skunk spray you pop them in the tub and depth charge them with tomato juice=) and rinse them off with the shower=)
