Australian physicist spots dictionary error
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From: Simple Simon on 12 May 2010 00:24 AFP - "An Australian physicist has uncovered an error in dictionary definitions that has likely stood uncorrected for a century." http://www.france24.com/en/20100511-australian-physicist-spots-dictionary-error
From: Peter Webb on 12 May 2010 03:54 "Simple Simon" <pi.r.cubed-nospam(a)gmail.com> wrote in message news:obpGn.7674$Gx2.532(a)newsfe20.iad... > AFP - > "An Australian physicist has uncovered an error in dictionary definitions > that has likely stood uncorrected for a century." > http://www.france24.com/en/20100511-australian-physicist-spots-dictionary-error > > Picky, picky, picky. Siphons need gravity *and* air pressure. They don't work in vacuums or in zero-g. If I was to pick one of these as they best description of the mechanism (and its a dictionary definition, not a physics lecture) I would probably go with air pressure as dictionaries do now; what pushes the fluid through the siphon is air pressure, it is the proximate mechanism. Note that you cannot use a siphon to go over an obstacle greater than 30 feet in height - this is neatly explained by air pressure, and inexplicable if you only consider gravity.
From: Uncle Al on 12 May 2010 10:02 Peter Webb wrote: > > "Simple Simon" <pi.r.cubed-nospam(a)gmail.com> wrote in message > news:obpGn.7674$Gx2.532(a)newsfe20.iad... > > AFP - > > "An Australian physicist has uncovered an error in dictionary definitions > > that has likely stood uncorrected for a century." > > http://www.france24.com/en/20100511-australian-physicist-spots-dictionary-error > > > > > > Picky, picky, picky. > > Siphons need gravity *and* air pressure. They don't work in vacuums or in > zero-g. [snip] A siphon requires gravitation, a closed conduit, and a fluid with tensile strength when inside the conduit. A vegetable oil siphon in hard vacuum is entirely reasonable if the oil is degassed beforehand. OTOH, try siphoning seltzer. -- Uncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/qz4.htm
From: Peter Webb on 12 May 2010 18:10 "Uncle Al" <UncleAl0(a)hate.spam.net> wrote in message news:4BEAB508.B3DFD96E(a)hate.spam.net... > Peter Webb wrote: >> >> "Simple Simon" <pi.r.cubed-nospam(a)gmail.com> wrote in message >> news:obpGn.7674$Gx2.532(a)newsfe20.iad... >> > AFP - >> > "An Australian physicist has uncovered an error in dictionary >> > definitions >> > that has likely stood uncorrected for a century." >> > http://www.france24.com/en/20100511-australian-physicist-spots-dictionary-error >> > >> > >> >> Picky, picky, picky. >> >> Siphons need gravity *and* air pressure. They don't work in vacuums or in >> zero-g. > [snip] > > A siphon requires gravitation, a closed conduit, and a fluid with > tensile strength when inside the conduit. Wrong. "Tensile strength" has nothing to do with it. > A vegetable oil siphon in > hard vacuum is entirely reasonable if the oil is degassed beforehand. Wrong. You cannot siphon anything in a vacuum. This is because (as the dictionary definition correctly states) it is air pressure which pushes the liquid through the siphon. > OTOH, try siphoning seltzer. > If by seltzer you mean carbonated beverage (eg Coca Cola), these siphon just fine. > -- > Uncle Al > http://www.mazepath.com/uncleal/ > (Toxic URL! Unsafe for children and most mammals) > http://www.mazepath.com/uncleal/qz4.htm
From: Greg Neill on 12 May 2010 18:51
Peter Webb wrote: > "Uncle Al" <UncleAl0(a)hate.spam.net> wrote in message > news:4BEAB508.B3DFD96E(a)hate.spam.net... >> Peter Webb wrote: >>> >>> "Simple Simon" <pi.r.cubed-nospam(a)gmail.com> wrote in message >>> news:obpGn.7674$Gx2.532(a)newsfe20.iad... >>>> AFP - >>>> "An Australian physicist has uncovered an error in dictionary >>>> definitions >>>> that has likely stood uncorrected for a century." >>>> http://www.france24.com/en/20100511-australian-physicist-spots-dictionary-error >>>> >>>> >>> >>> Picky, picky, picky. >>> >>> Siphons need gravity *and* air pressure. They don't work in vacuums or in >>> zero-g. >> [snip] >> >> A siphon requires gravitation, a closed conduit, and a fluid with >> tensile strength when inside the conduit. > > > Wrong. "Tensile strength" has nothing to do with it. > > >> A vegetable oil siphon in >> hard vacuum is entirely reasonable if the oil is degassed beforehand. > > Wrong. You cannot siphon anything in a vacuum. This is because (as the > dictionary definition correctly states) it is air pressure which pushes the > liquid through the siphon. Nope. A fluid with a tensile strength inside a conduit will act like an Atwood Machine with distributed mass. This will function just fine, even in vacuum. > >> OTOH, try siphoning seltzer. >> > > If by seltzer you mean carbonated beverage (eg Coca Cola), these siphon just > fine. Evolved bubbles of gas will collect at the high point of the closed tube. Unless the flow is fast enough to scour them away, eventually the siphon will be 'broken' by the gas gap. |