Yanking the chain on siphon claimsUniversity of Hawaiʻi at Hilo
Director, Media Relations, University Relations
A recent claim by an Australian physicist that the definition of “siphon” has been incorrect in most dictionaries, sometimes for decades as in the case of the Oxford English Dictionary, was recently re-examined by a professor and a student at the University of Hawaiʻi at Hilo.
Dr. Philippe Binder and Alex Richert have concluded that the new claim, widely spread over the web, is itself incorrect.
Dr. Stephen Hughes of Queensland University of Technology proposed that the unnatural upward flow of fluid that occurs within a siphon is caused by the difference in weight between the longer and shorter portions of fluid chains that move through the device. Binder and Richert surveyed historical siphon demonstrations and designed and performed several critical experiments.
In one of their setups, they managed to make water flow up the longer leg of a siphon and down the shorter one. They concluded that fluid flows up due to a higher pressure at the siphon entrance than at the bend, and upon reaching the bend the fluid is pulled down by gravity. The Hilo-based researchers have proposed a more precise dictionary definition that acknowledges both pressure and gravity as essential ingredients of the siphon mechanism but does not mention fluid chains or leg lengths.
Binder, an established researcher in the fields of chaos and complex systems, says that “nature has had her final word” through the outcomes of the experiments he and his student ran. He also remarks that the original story was quite appealing, and spread like fire through cyberspace with relatively little scrutiny: “it’s not true just because you read it on the web.”
Abraham Stroock, an associate professor of chemical engineering at Cornell University who has studied the upward flow of water in trees, concurs with Binder and Richert's conclusions. He points out that while the fluid chain model does not apply in standard human-made siphons, liquid water can act as a rope as it rises inside the narrow vessels of plants – a possible inspiration for future technology.
The work appears in the February 2011 issue of The Physics Teacher, a refereed journal published by the American Association of Physics Teachers. The paper is available online at www.phys.uhh.hawaii.edu/documents/TPT-final.pdf.