View source for Shower-curtain effect

{{Short description|Effect in physics}}
The '''shower-curtain effect''' in [[physics]] describes the phenomenon of a [[shower curtain]] being blown inward when a shower is running. The problem of identifying the cause of this effect has been featured in ''[[Scientific American]]'' magazine, with several hypotheses given to explain the phenomenon but no definite conclusion.

==Hypotheses ==

===Buoyancy hypothesis ===
{{see also|Cooling tower}}
Also called chimney effect or [[stack effect]], observes that warm air (from the hot shower) rises out over the shower curtain as cooler air (near the floor) pushes in under the curtain to replace the rising air.  By pushing the curtain in towards the shower, the (short range) vortex and [[Coandă effect]]s become more significant. However, the shower-curtain effect persists when cold water is used, implying that this is not the sole mechanism.<ref name=straight>{{cite web|url=http://www.straightdope.com/columns/read/1369/why-does-the-shower-curtain-blow-in-despite-the-water-pushing-it-out-revisited|title=Why does the shower curtain blow in despite the water pushing it out (revisited)?|website=[[The Straight Dope]]|date=2001-08-10|access-date=2014-01-29|archive-date=2014-02-03|archive-url=https://web.archive.org/web/20140203043758/http://www.straightdope.com/columns/read/1369/why-does-the-shower-curtain-blow-in-despite-the-water-pushing-it-out-revisited|url-status=live |first=Cecil |last=Adams |author-link=Cecil Adams}}</ref>

===Bernoulli effect hypothesis ===
The most popular explanation given for the shower-curtain effect is [[Bernoulli's principle]].<ref name=straight/>  Bernoulli's principle states that an increase in velocity results in a decrease in pressure.  This theory presumes that the water flowing out of a [[shower head]] causes the air through which the water moves to start flowing in the same direction as the water.  This movement would be parallel to the plane of the shower curtain.  If air is moving across the inside surface of the shower curtain, Bernoulli's principle says the air pressure there will drop.  This would result in a pressure differential between the inside and outside, causing the curtain to move inward.  It would be strongest when the gap between the bather and the curtain is smallest, resulting in the curtain attaching to the bather.<ref>{{Cite web |last=Wakeham |first=David |title=The shower curtain effect |url=https://hapax.github.io/physics/everyday/shower/ |access-date=2024-11-03 |website=hapax.github.io}}</ref>

===Horizontal vortex hypothesis ===
A computer simulation of a typical bathroom found that none of the above theories pan out in their analysis, but instead found that the spray from the [[Shower head|shower-head]] drives a horizontal [[vortex]]. This vortex has a low-pressure zone in the centre, which sucks the curtain.<ref name="straight" /><ref>{{cite web| url=http://zidbits.com/2010/11/the-shower-curtain-effect/| title=What Is The Shower Curtain Effect?| date=2010-11-17| accessdate=2011-06-29| archive-date=2011-05-27| archive-url=https://web.archive.org/web/20110527044938/http://zidbits.com/2010/11/the-shower-curtain-effect/}}</ref>

David Schmidt of the University of Massachusetts was awarded the 2001 [[Ig Nobel Prize]] in Physics for his partial solution to the question of why shower curtains billow inwards. He used a [[computational fluid dynamics]] code to achieve the results.  Professor Schmidt is adamant that this was done "for fun" in his own free time without the use of grants.<ref>{{cite magazine|url=https://www.wired.com/science/discoveries/news/2001/10/47334|title=Shower Curtain Rises on Ig Nobels|magazine=Wired |archive-url=https://archive.today/20140324141230/http://www.wired.com/science/discoveries/news/2001/10/47334 |archive-date=2014-03-24 |date=2001-10-05|last1=Manjoo|first1=Farhad |author-link=Farhad Manjoo}}</ref>

===Coandă effect===
The [[Coandă effect]], also known as "boundary layer attachment", is the tendency of a moving fluid to adhere to an adjacent wall.<ref name=straight/>

==References==
{{Reflist}}

==External links==
* [http://www.sciam.com/article.cfm?id=why-does-the-shower-curta Scientific American: Why does the shower curtain move toward the water?]
* [http://www.straightdope.com/classics/a2_104.html Why does the shower curtain blow up and in instead of down and out?]
* [https://www.youtube.com/watch?v=-Ffa5zHBPFQ Video demonstration of how this phenomenon could be solved.]
* [http://www.straightdope.com/columns/010810.html The Straight Dope: Why does the shower curtain blow in despite the water pushing it out (revisited)?]
* [http://improbable.com/ig/ig-pastwinners.html 2001 Ig Nobel Prize Winners]
* [https://web.archive.org/web/20060207093353/http://www.fluent.com/about/news/newsletters/01v10i2/a8.htm Fluent NEWS: Shower Curtain Grabs Scientist – But He Lives to Tell Why]
* [https://www.npr.org/templates/story/story.php?storyId=6430581 Arggh, Why Does the Shower Curtain Attack Me? by Joe Palca]. ''[[All Things Considered]]'', [[National Public Radio]].  November 4, 2006. (audio)
* [http://www.opticsinfobase.org/ao/abstract.cfm?id=43553 Experimental Investigation of the Influence of the Relative Position of the Scattering Layer on Image Quality: the Shower Curtain Effect]
* [http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31415&fbodylongid=862 The shower curtain effect; ESA ]

[[Category:Fluid dynamics]]
[[Category:Physical phenomena]]
[[Category:Unsolved problems in physics]]
[[Category:Bathing]]