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From: Mark Olson on 10 Feb 2010 10:40 Catman wrote: > Mark Olson wrote: >> Kevin Gleeson wrote: >>> On Wed, 10 Feb 2010 08:34:46 -0600, Mark Olson <olsonm(a)tiny.invalid> >>> wrote: >>> >>>> Kevin Gleeson wrote: >>>>> On Wed, 10 Feb 2010 15:00:58 +0100, doetnietcomputeren >>>>> <doesnotcompute(a)gmail.com> wrote: >>>>> >>>>>> On 2010-02-10 14:55:01 +0100, Kevin Gleeson >>>>>>> Oh - btw, 3 degree water doesn't exist unless someone added >>>>>>> alcohol to >>>>>>> it. It stops at 4C then the next phase change is ice. >>>>>> What? Surely the freezing point of normal water is 0 degrees C, >>>>>> and lower still for salt water? >>>>> Nope there is a point where it has to drop energy to go through the >>>>> phase change to ice. I don't have links and can't be arsed looking, >>>>> but seawater will only go to 4C. Th energy to do the phase change is >>>>> worth those other 3C. Google it. I'm sure it is out there somewhere. >>>> You are confused. Fresh water freezes at 0C, sea water at less than >>>> zero C. This link has a likely explanation of your 4C confusion. >>>> >>>> http://www.tpub.com/content/aerographer/14269/css/14269_62.htm >>> >>> Fair call, I was going on 30 year old dive training memory and was >>> told that you couldn't dive in water less then 4C as it didn't exist. >>> Your explanation there is more succinct but still gives the same >>> result. There is still that phase change at 4C ( and that article >>> explains that the change is rapid), but my memory (or people's >>> understanding of it when I was doing physics and dive training) still >>> means you are unlikely to dive in water under 4C. >> >> The simple fact is fresh water does indeed freeze at 0C and not 4C. >> Sea water freezes at some lower temperature depending on the salinity. >> There is no phase change at 4C. "Phase change" has a specific meaning. >> >> > There is, if memory serves, a re-arrangement of liquid molecules in the > water that occurs at adn below 4C which accounts for the density of ice > being less than that of liquid H2O (generally)? > From the above link: "Freshwater reaches maximum density at 4�C (39�F). In effect, as freshwater ponds and lakes cool, and the surface waters reach 4�C the water sinks and warmer subsurface water rises to replace it. This slows the process of cooling the surface of the pond below 4�C until the entire body of water is cooled to 4�C. After this point, surface waters cooled to less than 4�C are slightly less dense than the water below the surface, and cooling to the freezing point is rapid." My point about the specific meaning of "phase change" is important- there are changes in water density around 4C but that is not a phase change.
From: Simian on 10 Feb 2010 10:41 Catman wrote: > Mark Olson wrote: > > Kevin Gleeson wrote: > > > > > > Fair call, I was going on 30 year old dive training memory and was > > > told that you couldn't dive in water less then 4C as it didn't > > > exist. Your explanation there is more succinct but still gives > > > the same result. There is still that phase change at 4C ( and > > > that article explains that the change is rapid), but my memory > > > (or people's understanding of it when I was doing physics and > > > dive training) still means you are unlikely to dive in water > > > under 4C. > > > > The simple fact is fresh water does indeed freeze at 0C and not 4C. > > Sea water freezes at some lower temperature depending on the > > salinity. There is no phase change at 4C. "Phase change" has a > > specific meaning. > > > There is, if memory serves, a re-arrangement of liquid molecules in > the water that occurs at adn below 4C which accounts for the density > of ice being less than that of liquid H2O (generally)? The two forms of water (crystalline and amorphous) exist in a dynamic equilibrium all the way up to it's boiling point, and all the way down to (and probably below) it's freezing point. The warmer it gets, the less crystalline areas (err, volumes) there are. The crystalline volumes are less dense than the amorphous ones. At 4C, the reduction in crystalline water (and thus increase in density) is overtaken by the general decrease in density due to temperature increase. When frozen, water is mostly crystalline - I seem to remember that there are bits, like crystal surfaces, that retain some amorphous
From: Catman on 10 Feb 2010 11:01 Mark Olson wrote: > Catman wrote: >> Mark Olson wrote: >>> Kevin Gleeson wrote: >>>> On Wed, 10 Feb 2010 08:34:46 -0600, Mark Olson <olsonm(a)tiny.invalid> >>>> wrote: >>>> >>>>> Kevin Gleeson wrote: >>>>>> On Wed, 10 Feb 2010 15:00:58 +0100, doetnietcomputeren >>>>>> <doesnotcompute(a)gmail.com> wrote: >>>>>> >>>>>>> On 2010-02-10 14:55:01 +0100, Kevin Gleeson >>>>>>>> Oh - btw, 3 degree water doesn't exist unless someone added >>>>>>>> alcohol to >>>>>>>> it. It stops at 4C then the next phase change is ice. >>>>>>> What? Surely the freezing point of normal water is 0 degrees C, >>>>>>> and lower still for salt water? >>>>>> Nope there is a point where it has to drop energy to go through the >>>>>> phase change to ice. I don't have links and can't be arsed looking, >>>>>> but seawater will only go to 4C. Th energy to do the phase change is >>>>>> worth those other 3C. Google it. I'm sure it is out there somewhere. >>>>> You are confused. Fresh water freezes at 0C, sea water at less than >>>>> zero C. This link has a likely explanation of your 4C confusion. >>>>> >>>>> http://www.tpub.com/content/aerographer/14269/css/14269_62.htm >>>> >>>> Fair call, I was going on 30 year old dive training memory and was >>>> told that you couldn't dive in water less then 4C as it didn't exist. >>>> Your explanation there is more succinct but still gives the same >>>> result. There is still that phase change at 4C ( and that article >>>> explains that the change is rapid), but my memory (or people's >>>> understanding of it when I was doing physics and dive training) still >>>> means you are unlikely to dive in water under 4C. >>> >>> The simple fact is fresh water does indeed freeze at 0C and not 4C. >>> Sea water freezes at some lower temperature depending on the salinity. >>> There is no phase change at 4C. "Phase change" has a specific meaning. >>> >>> >> There is, if memory serves, a re-arrangement of liquid molecules in >> the water that occurs at adn below 4C which accounts for the density >> of ice being less than that of liquid H2O (generally)? >> > > From the above link: > > "Freshwater reaches maximum density at 4�C (39�F). In effect, as freshwater > ponds and lakes cool, and the surface waters reach 4�C the water sinks and > warmer subsurface water rises to replace it. This slows the process of > cooling the surface of the pond below 4�C until the entire body of water is > cooled to 4�C. After this point, surface waters cooled to less than 4�C are > slightly less dense than the water below the surface, and cooling to the > freezing point is rapid." > > My point about the specific meaning of "phase change" is important- there > are changes in water density around 4C but that is not a phase change. > > Sorry, I did not mean to imply that there was :) -- Catman MIB#14 SKoGA#6 TEAR#4 BOTAFOF#38 Apostle#21 COSOC#3 Tyger, Tyger Burning Bright (Remove rust to reply) 116 Giulietta 3.0l Sprint 1.7 GTV TS GT 3.2 V6 Triumph Sprint ST 1050: It's blue, see. www.cuore-sportivo.co.uk
From: Catman on 10 Feb 2010 11:02 Wicked Uncle Nigel wrote: > Using the patented Mavis Beacon "Hunt&Peck" Technique, Catman > <catman(a)rustcuore-sportivo.co.uk> typed >> Wicked Uncle Nigel wrote: >>> Using the patented Mavis Beacon "Hunt&Peck" Technique, Catman >>> <catman(a)rustcuore-sportivo.co.uk> typed >>>>> >>>> There is, if memory serves, a re-arrangement of liquid molecules in >>>> the water that occurs at adn below 4C which accounts for the density >>>> of ice being less than that of liquid H2O (generally)? >>> >>> <http://www.newscientist.com/article/mg20527466.200-the-strangest-liqui>>d- >>> >>> why-water-is-so-weird.html> >>> >> >> Ooh, ta. > > De nada. By a curious coincidence I was reading that on the shitter this > very morning. > Dare I ask your device of choice for such moments? -- Catman MIB#14 SKoGA#6 TEAR#4 BOTAFOF#38 Apostle#21 COSOC#3 Tyger, Tyger Burning Bright (Remove rust to reply) 116 Giulietta 3.0l Sprint 1.7 GTV TS GT 3.2 V6 Triumph Sprint ST 1050: It's blue, see. www.cuore-sportivo.co.uk
From: doetnietcomputeren on 10 Feb 2010 11:08
On 2010-02-10 17:02:19 +0100, Catman <catman(a)rustcuore-sportivo.co.uk> said: >>>> <http://www.newscientist.com/article/mg20527466.200-the-strangest-liqui>>d- >>>> why-water-is-so-weird.html> >>>> >>> >>> Ooh, ta. >> >> De nada. By a curious coincidence I was reading that on the shitter >> this very morning. >> > > Dare I ask your device of choice for such moments? Armitage shanks at a guess. -- Dnc |