swansont Posted January 5, 2005 Share Posted January 5, 2005 Nave, we already discussed the part that causes that: As some of the boiling water is in steam form, and more of it is in steam or less-scarce form when it's thrown, of course it freezes (at least partially) faster than the room temp water. But obviously, if you have a 5 C cup of water in the freezer and a similar sized 50 C cup of water in the freezer, the 5 C water freezes faster. Unless there's a lot of evaporation, so that the amount of water that has to freeze is less, and that allows it to "catch up" to the colder cup. Link to comment Share on other sites More sharing options...
jdurg Posted January 5, 2005 Share Posted January 5, 2005 Unless there's a lot of evaporation, so that the amount of water that has to freeze is less, and that allows it to "catch up" to the colder cup. The amount of water that cold air can hold is VERY small, so evaporation will not play any significant role. Link to comment Share on other sites More sharing options...
YT2095 Posted January 5, 2005 Share Posted January 5, 2005 The amount of water that cold air can hold is VERY small, so evaporation will not play any significant role. True! I rem in Canada, the winters there would get to -40c routinely, and the Air was drier than the Sahara desert! (nose bleeds though the dryness were common for us unaclimatised Brits). Link to comment Share on other sites More sharing options...
swansont Posted January 5, 2005 Share Posted January 5, 2005 The amount of water that cold air can hold is VERY small, so evaporation will not play any significant role. Again, "under some circumstances" has to be appended. Your statement is not an absolute truth. Link to comment Share on other sites More sharing options...
CMN Posted January 5, 2005 Share Posted January 5, 2005 I was under the impression that hot water freezes first If you have equal volumes of boiling and room temperature water in a container the hot water can actually freeze faster. I reckon that there are some good reasons for it aswell: Convection is one, when some of the water cools at it will mix with the hotter water bringing down the temperature. Evapourtion is another one to be taken in to account the boiling water will loose some of its volume It can depend on the container and its insulating values aswell. That would be my impression but im not entirely sure Link to comment Share on other sites More sharing options...
jdurg Posted January 5, 2005 Share Posted January 5, 2005 Well, you also have to remember that 'coldness' doesn't flow. Heat will flow from one object to another, but cold will not 'flow'. Things only feel cold because you sense the heat moving from your body into the thing at a lower temperature. Water also has a very high specific heat capacity. It takes a good amount of energy for one gram of water to change one degree Kelvin. For the cooling, the water has to give out about 4 kJ (I can't remember the right unit) of energy per gram of water in order to drop one degree Kelvin. It doesn't matter if the water's at 90 or 9 degrees Celcius. It still needs to 'give away' that energy to drop in temperature. So the amount of energy that cold water has to give up in order to freeze is a lot less than the amount of energy that hot water has to give up in order to freeze. The only way to speed up the freezing process is to put the water in direct contact with something that has a lower specific heat. This way it can transfer its energy much quicker. With the hotter water there is some convection going on as the water at the surface will cool and move down to the bottom of the container since colder water is denser than warm water. However, less noticeable convection is occuring with the colder water as well. With the boiling water, when you take it off of the heat source and put it into the cold, the boiling process will cease and you'll lose any added 'loss of volume' due to the boiling. Evaporation will also soon cease as the air will become saturated with water and you'll see it condensing out and forming a fog. This air which is initially warmed up will also be cooled down by the massive amount of cooler air surrounding it. Therefore, after the first few seconds of being out there, the advantage of the higher water vapor levels will soon break down. Scientifically speaking, if you have two containers of water that are exact in EVERY single manner except for the temperature of the water inside those containers, the hotter water CANNOT freeze any sooner than the cooler water. This is providing that you have the same container with the same insulation in the same environment with the same volume, etc. etc. As for why the boiling water thrown in the air seems to freeze, I think I have an idea on why that happens. When you throw water in the air, the surface area increases dramatically. With boiling water, it means that more hot water is exposed to cooler air. As a result, the temperature of the air surrounding the hot water will increase allowing more water vapor to exist. However, since there is so much more cold air out there, the air temperature will soon drop again causing all that water vapor to condense back into water and ice crystals. As a result, you'll see the ice crystals forming from the condensing water vapor. With cold water, it won't raise the temperature of the air appreciably so you won't get a sudden saturation of water vapor. No water vapor means no water to condense out which means no appearance of ice crystals. The ice has an easier time forming out of condensed water vapor because the mass of the water is less than it would be in the case of a puddle. Link to comment Share on other sites More sharing options...
CMN Posted January 5, 2005 Share Posted January 5, 2005 Even if you have everything the same hot water will freeze faster than cold water under some conditions. I think ill try it out with some ice trays and see what happens Link to comment Share on other sites More sharing options...
YT2095 Posted January 5, 2005 Share Posted January 5, 2005 did anyone actualy READ this link I gave? http://math.ucr.edu/home/baez/physics/General/hot_water.html and if you did, what are your opinions? Link to comment Share on other sites More sharing options...
jdurg Posted January 5, 2005 Share Posted January 5, 2005 did anyone actualy READ this link I gave? http://math.ucr.edu/home/baez/physics/General/hot_water.html and if you did' date=' what are your opinions?[/quote'] The link is VERY detailed, but I immediately saw a problem. Not once did they show an experiment where the water was the same or in the same conditions. To prove it true, it would have to happen on a consistant basis, which they failed to show, and they'd have to use the same water. It seems as if they made no effort to de-gas both waters and allowed far too many variables to be introduced into the experiments. Plus, they also mentioned water freezing without much ice forming! FROZEN WATER IS ICE! If no ice formed, it didn't freeze. lol. I also wonder what definition they are using of 'freezing'. Do they mean a thin layer of ice on the surface, or the entire mass of water being solid? While undoubtably the hot water may have a layer of ice on the top of it, that layer of ice will insulate the warmer water underneath and not allow it to freeze as quickly. Meanwhile, the cooler water would form a consistent mass of ice throughout. Frankly, I didn't see much proof of anything in there. It would be like saying sample 1 of liquid A ignites easier than sample 2 of liquid A without taking into account the fact that sample 1 has some gasoline mixed in with it. Link to comment Share on other sites More sharing options...
CMN Posted January 6, 2005 Share Posted January 6, 2005 Freezing water is water at 0 degrees, but if a body of water is at 0 degrees it wont neccesarily(i cant spell i know or i can spell and i dont know it ) all be solid. The body of water will take a while to freeze because of latent heats....... I think...... Link to comment Share on other sites More sharing options...
Ophiolite Posted January 6, 2005 Share Posted January 6, 2005 So you're making the distinction, a fair one, that freezing water is in the process of becoming frozen; frozen water is ice (solid), freezing water is water (liquid). Link to comment Share on other sites More sharing options...
CMN Posted January 7, 2005 Share Posted January 7, 2005 Exactly which means that when water is freezing it can still be a liquid. Latent heat and all that malarky Link to comment Share on other sites More sharing options...
jdurg Posted January 7, 2005 Share Posted January 7, 2005 That is why it's so VERY important to specifically define every term you use. I know some people who will see a layer of ice on top of a lake and say that the lake is frozen. I only consider a mass of water frozen when it is solid 100% throughout. So to me, that lake isn't frozen. Only the layer of water on the top of it is. Link to comment Share on other sites More sharing options...
swansont Posted January 7, 2005 Share Posted January 7, 2005 The link is VERY detailed, but I immediately saw a problem. Not once did they show an experiment where the water was the same or in the same conditions. To prove it true, it would have to happen on a consistant basis, which they failed to show, and they'd have to use the same water. It seems as if they made no effort to de-gas both waters and allowed far too many variables to be introduced into the experiments. Yes, but that's part of the point. All things are not equal in this effect. Plus' date=' they also mentioned water freezing without much ice forming![/quote'] To what section are you referring? Link to comment Share on other sites More sharing options...
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