Cecil’s job of fighting ignorance is hard work, but undoubtedly it is worth it watching the rest of the world occasionally claw their way into enlightenment. In this case, it is the famous ‘Why does the shower curtain blow in?’ question addressed by Cecil here: http://www.straightdope.com/classics/a2_104.html
According to the Boston Globe (story with more detail http://www.boston.com/dailyglobe2/205/science/Shower_power+.shtml), a U-Mass engineer running a complex flow modeling program has determined that air is pushed along by the water from the shower, then hits the wall of the shower and is deflected up and over and around to form a rotating vortex. (the axis of the vortext is along the line from the curtain to the back wall) The vortex creates low pressure at its center which pulls the curtain in.
While similar to the SD column’s explanation, this latest research goes beyond it, and particularly highlights ‘the importance of the walls of the shower’ (I bet you never thought that you’d see that phrase in this context, eh?) . In the column, Cecil claims that his lack of detail on this subject is due to being “overcome with an exquisite languor.” I prefer to think that he is following the path of great teachers, dropping just enough hints to help mankind (and womankind and, uh, it-kind) struggle up their own path to knowledge, made stronger by the effort.
Welcome to the board, oak-person! Your name brought back memories of high-school latin, when we were told “names ending in -us are masculine except for names of trees”.
With all due respect to the Boston Globe, it seems that their competitor the New York Times has beat them to the punch, as can be seen in this thread.
As the unofficial Straight Dope Boston correspondent for shower curtain issues, I’m going to point out the Boston Globe’s editorial today congratulating David Schmidt for his work. http://www.boston.com/dailyglobe2/211/editorials/Not_so_silly_science+.shtml
The Globe is saying, 'yes, it seems a bit silly for science, but still worthwhile - who knows what useful insights could come out of it, and anyway, helping people understand their world is a good thing."
No mention of Cecil’s clear pivotal role in spurring further research, but that’s undoubtedly due to the Globe honoring his modesty.
I think most of the discussions about vortices are so much hot air. Wouldn’t you think that a vortex strong enough to pull the curtains in would be noticeable by the occupant?
Occam’s razor should appy here and the simplest answer should be hot air.
The hot water heats up the air, which rises, coupled with the lack of openings at the bottom and a large opening at the top produces a pressure difference that causes the curtains to suck in.
Without pausing for deep consideration (deep consideration’s on vacation until the fourth week of August), it seems to me that an immediate test of the effects of vortices versus those of heated air (my grass roots fave) could be tested by observation of the behavior of the shower curtain during the (dreaded) cold shower.
I should add the observation that I can frequently prevent (or at least reduce) the dreaded clingy curtain behaviour by leaving a moderate gap (6 or 8 inches) between the end curtain and the wall - preferably the end away from the shower head. This allows the air that desires to enter a free path, thus reducing the inward force on the curtain.
As for the question about why don’t we feel the vortex in the shower, it’s because when we’re standing under the stream, we’re part of the wall. When we’re not standing under the stream, we’re too busy fighting off the shower curtain to notice, and we’re more likely to notice the incoming cool air than the rotating warm air.
And, I should note that the model does NOT disprove the chimney hypothesis. It could well be that these two effects combine somehow.
And finally, another way to test the hypothesis would be to set up some system of baffle that would defeat the vortex, but not prevent the chimney or Bernoulli effects.
What amazes me is that anyone would actually admit to having shower curtains. They are so low rent. Shower curtains haven’t been used since, say, mid-70s, and rarely then. Still, I am speaking Australia. Perhaps other countries actually like disgusting, ineffective, mouldy sheets of plastic flapping around their legs while trying to bathe.
Unless there are those who have a drastically different shower curtain setups than the countless shower curtains I have encountered in my lifetime, then this vortex is an explanation in search of a cause.
I’m sure that the science behind the article is accurate and laudable, but it is not the cause of the dreaded shower curtain shimmy. As anyone who has taken a long hot shower knows (and has been previously noted in this thread by partyofone) - the effect practically disappears as the temperature of the air outside of the shower begins to balance with that inside the stall. Just open the bathroom door to get the curtain to start to pull to the inside again. Being of a scientific nature, I just went and proved said effect with a nice long hot shower. As soon as the air throughout the closed bathroom steamed up the curtain fell dormant. A few short seconds after leaving the bathroom door open while the hot water continued to flow caused the curtain to bow again.
It should also be noted that it is important to make sure that no water comes between the curtain and the wall of the tub, as it will have the effect of holding down the curtain even with the change in hot/cold air pressure. Also, if it were truly a vortex at issue the effect should not persist once a person is blocking the stream of water. Anyone who has struggled to keep a curtain tame knows that it will blow as long as the air outside is much cooler than the air inside (and vice versa one would assume). If a vortex was the cause, the effect would drop considerably once the water was not able to create a focused turbulence in the air.
I think Cecil may get a soaking for thinking a vortex is the predominant cause for this effect…
Did anybody else notice that the shower vortex illustrated by **Slug ** is rotating in the wrong direction? The vortex is to the left of the shower spray, so it should be rotating clockwise; yet it is clearly rotating widdershins. What’s going on here? Is this, perhaps, an Australian shower, where all things rotational are backwards?
The computer modeling is cool, but where is the person? The model doesn’t take into account the presence of a 5’5" 150 lb or so, human body. Wouldn’t the presence of a person greatly affect the development of a vortex? I’m no engineer, but the presence of a person would seem to hamper the development of a vortex and/or, if you claim the person now becomes the ‘back wall’ of the shower, that the vortex would be much smaller, therefore weaker…
Fear Itself: yeah, I noticed that too. But Slug drew what looks like elongated curved arrowheads, as though the vortex (with its cutesie evil little smile ) was trying to point the way it was rotating. Or something.
Cecil made a few tiny mistakes in his explanation of the Shower Curtain solution.
First you can not ignore Bernoulli’s theory when dealing with this problem as Cecil states at the end of the article. Cecil was trying to say that the wing lift explanation for the shower curtain is not correct. However, Bernoullis’s equation go far beyond that one physical phenomenom. Bernoulli’s equation is a mathematical discription of the flow of fluid due to pressure differences. The entire solution is exactly what the Bernoulli’s equations are used for.
The center of the vortex has a lower pressure than the surrounding pressure. Why? It has a lower pressure because of the difference in the velocities of the air in the vortex from the center out. At the center the air is virtually standing still. At the edges it is at its fastest. This difference is what causes the low pressure and is exactly what Bernoulli’s equations describe.
Now then, this low pressure in the center then causes a pressure difference between the shower side of the curtain and the bathroom side. This pressure difference causes the air to move and subsequently the curtain. This again is exactly what Bernoulli’s equation describes.
When Cecil states we can ignore Bernoulli he was incorrect.
Secondly in his column Cecil again uses the layman’s term suck to describe the force that moves the curtain. This is incorrect. The term suck has no definition in Physics. People use this term because they don’t understand what is going on because at times physics is not intuitive. This counter intuitive nature of some physical effects is what also gives us the term centrifical force. What REALLY happens is the air molecules inside the shower bump into the curtain less frequently and with less force than the bathroom side of the curtain. This difference in molecular bumping causes a net positive force on the bathroom side and allows the curtain to be moved.
this shower curtain phenomena is all well and good but whats the deal with “a guy like Jearl, who plunged his hand into a pot of molten lead on the Johnny Carson show to demonstrate the Leidenfrost effect” ?! YIKES!
I have a simple question. Where does the air go to?
If a vortex is produced and has low pressure at the centre, then air from outside will flow in to fill the vacuum. Unless this new air goes somewhere the centre of the vortex will stop being at negative pressure and the process will stop.
The drawings only show air being entrapped into a vortex. Not a process to vent it elsewhere.
[My idol is Dr. Frink on the Simpsons]
I think that this squabble over the Bernoulli effect is all hot water. I’ll try to review this argument & re-post.
The shower hurricane theory seems unlikely to hold up under real world examination. The shower curtain continues to come into the shower even when the water flow is interrupted by the presence of a human. At least, that is my own real world experience.
Those who feel the chimney effect explains the situation should address the fact noted by Cecil that the shower curtain blows in even in the presence of cold water. While the effect is lessened, the continued existence of an effect would appear to discount rising heated air as the cause.
) was trying to point the way it was rotating. Or something.
I’ll try to review this argument & re-post.