<!--QuoteBegin--Venmoch+Apr 22 2003, 02:00 PM--></span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td><b>QUOTE</b> (Venmoch @ Apr 22 2003, 02:00 PM)</td></tr><tr><td id='QUOTE'><!--QuoteEBegin--> And this enriches my worthless life how??? <!--QuoteEnd--> </td></tr></table><span class='postcolor'> <!--QuoteEEnd--> It's useful if you need ice cubes in a hurry, and with Summer just around the corner...
From that link (which was good), it sounds like it varies wildly, depending on how much water, how much of a difference in temperature, and even the shape of the container. Interesting stuff, though. Wouldn't have thought of the convection currents angle.
you need to give alot more of the variables then just cold water and hot water. I mean if i got a bucket and its at 1 degree celcius and you have one at 50 degrees celcius at 200 atmospheres guess which one will freeze faster <!--emo&;)--><img src='http://www.unknownworlds.com/forums/html/emoticons/wink.gif' border='0' style='vertical-align:middle' alt='wink.gif'><!--endemo-->
Yeah..... this, in most cases, is a bunch of crap...
It even said how so many conditions are needed, this isn't an "effect" more like a "phonomina"
And some posted asked about 0degree water, it is possible, in fact, all water goes to zero degrees celcius before it even STARTS to freeze. It takes 4.18joules per ml of water to lower the temperature 1 degree celcius, when it hits 0 degrees, then the joules of heat are taken from the bonds and the water freezes.
It's interesting to me...but I'm learning to be a mechanical engineer, so what's interesting to me is boring to the rest of the world. It's important to point out that in many situations hot water does freeze more slowly than cold water, as is intuitive. The situations in which hot water cools faster seem to be a deviation from this norm. I'm curious if this phenomenon is for water only. H20 seems to have some strange properties. It becomes less dense when it freezes, and freezes from the top (because of the density thing I believe)...and now I'll shut up. Geeze, what was i thinking?
Imagine a deep lake. Now, lets say its at 20 or so Celsius. Now, the water at the top is continuously being cooled because of the environment. Now, the top of the water drops temperature steadily until it hits 4 degrees celsius at which point, this is a phenomena, it becomes more dense then water at any other temperature, including temperatures colder than 4 degrees. Now, because it is more dense, it sinks to the bottom of the lake and the top of the water is replaced with the warmer water, so the water doesn't freeze until the entire body of water is the same temperature. Now, winter last only so long in most places, sometimes, the length of winter is not long enough to cool an entire body of deep water, therefore, some deeper bodies of water never freeze over.
Heh, not to be a dork but I remember from one of my physics classes that you can deduce that cold water will freeze quicker than hot water based on the equation Q=mc*(change in temperature). m is the mass of the water, c is a constant that would be the same if you performed the test. The only difference would be the initial temperatures for the 2 bodies of water. What you would see is that the hot water would have to lose more energy than cold water. Ex. suppose 10 degrees C and 20 for the other. The hotter water would have to burn off 2x the energy to freeze as compared to the colder water.
Ok, you're sorta right colt but not quite. What you posted is a change in "heat" equation. This has nothing to do really with how fast it cools. The rate of change in heat, or the heat flow, is the determining factor.
Also this really isn't important but I'll point it out just for accuracy sake. 20 degrees C does NOT have twice as much energy as 10 degrees C. In order to determine the total energy using the equation you posted you would have to compute the heat, Q, that would be needed to go from say 10C to absolute zero, -273.15 degrees C. You don't use 0 degrees celsius to compute the heat is it ignores 270 odd degrees of temperature. Absolute zero is when all atomic movement ceases and the system has no energy whatsoever. The system still has plenty of atomic movemtn and thus energy at 0 celsius. So 20 degrees has maybe 3 or 4 percent more energy that 10 degress, definately not twice as much.
One thing which was suggested there was that hot water will melt any ice that it is sitting on, which will then freeze again with a lot more contact to your vessel than the cold water gets, so cooling after this will faster as there is less insulating air between the container and you heat sink.
ThansalThe New ScumJoin Date: 2002-08-22Member: 1215Members, Constellation
/me thinks this counts as wasted lines in the database <!--emo&:p--><img src='http://www.unknownworlds.com/forums/html/emoticons/tounge.gif' border='0' style='vertical-align:middle' alt='tounge.gif'><!--endemo-->
Comments
Hot water because of frost bite?
They are guesses. (sp?)
Cold water = Ice (d0h)
There's no such thing as over 0 degrees celsius cold water.
warm water freezes faster
It's useful if you need ice cubes in a hurry, and with Summer just around the corner...
... feh, I don't know.
It even said how so many conditions are needed, this isn't an "effect" more like a "phonomina"
And some posted asked about 0degree water, it is possible, in fact, all water goes to zero degrees celcius before it even STARTS to freeze. It takes 4.18joules per ml of water to lower the temperature 1 degree celcius, when it hits 0 degrees, then the joules of heat are taken from the bonds and the water freezes.
<a href='http://www.straightdope.com/classics/a2_098b' target='_blank'>http://www.straightdope.com/classics/a2_098b</a>
yup, same here
Generally speaking, cold water freezes first.
The hot water will cool much faster because of the large difference, because of the differential temperature formula or whatever I really don't care.
I've got one for you though.
How come the deeper the water the longer it takes to freeze at the top ?
It's really not quite so simple.
Alright, Here we go.
Imagine a deep lake. Now, lets say its at 20 or so Celsius. Now, the water at the top is continuously being cooled because of the environment. Now, the top of the water drops temperature steadily until it hits 4 degrees celsius at which point, this is a phenomena, it becomes more dense then water at any other temperature, including temperatures colder than 4 degrees. Now, because it is more dense, it sinks to the bottom of the lake and the top of the water is replaced with the warmer water, so the water doesn't freeze until the entire body of water is the same temperature. Now, winter last only so long in most places, sometimes, the length of winter is not long enough to cool an entire body of deep water, therefore, some deeper bodies of water never freeze over.
Ex. suppose 10 degrees C and 20 for the other. The hotter water would have to burn off 2x the energy to freeze as compared to the colder water.
Also this really isn't important but I'll point it out just for accuracy sake. 20 degrees C does NOT have twice as much energy as 10 degrees C. In order to determine the total energy using the equation you posted you would have to compute the heat, Q, that would be needed to go from say 10C to absolute zero, -273.15 degrees C. You don't use 0 degrees celsius to compute the heat is it ignores 270 odd degrees of temperature. Absolute zero is when all atomic movement ceases and the system has no energy whatsoever. The system still has plenty of atomic movemtn and thus energy at 0 celsius. So 20 degrees has maybe 3 or 4 percent more energy that 10 degress, definately not twice as much.
One thing which was suggested there was that hot water will melt any ice that it is sitting on, which will then freeze again with a lot more contact to your vessel than the cold water gets, so cooling after this will faster as there is less insulating air between the container and you heat sink.
This mainly applies to freezers, I guess.
I fully agree <!--emo&:D--><img src='http://www.unknownworlds.com/forums/html/emoticons/biggrin.gif' border='0' style='vertical-align:middle' alt='biggrin.gif'><!--endemo-->