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How Ice Melts
Killer Instinct writes "Ever wonder how ice melts? Until now, scientists could not explain why ice cubes in your drink melt. They've known the basics, but the details remained elusive. A breakthrough new study, announced yesterday, supports a leading theory that melting starts when the fundamental structure of matter begins to crack. Melting is considered a basic phenomenon in physics. An understanding of how it works is crucial to gaining a firm grasp on the physical world."
No.
A guy walks into a bar... well, I forgot the joke, but the punchline is that he's an alcoholic.
I can finally sleep at night!
This is somewhat akin to boiling really, at least from my perspective.. small nucleation points, that spread throughout the liquid or crystal, effecting an overall phase change when the energy distribution reaches a point such that the majority of atoms prefer the gaseous or liquid state (depending on the phase change).
Wait wait wait, let me get this straight. We put a man on the moon, developed flying machines composed of several hundred tons of steel, and we just now BARELY explain why Ice Cubes melt in our drink? You know, sometimes humanity really is....scary. What'll be truly frightning is if scientists come out with an explanation as to why Ice Cube still gets movie roles.
a. Summary is plagiarized from the article, unless I've missed some nested quotes.
b. These guys took this problem because "the earliest phase of melting has never been seen" but they didn't do that either! All they did was make "see-through crystals that are like small beads and are visible in an optical microscope." Doesn't sound like a hell of a lot of progress to me; anyone care to elaborate?
c. Their main result seems to be that the melting process starts at crystal defects and spreads to create liquidy regions within the crystal. Again, can anyone explain why the melting might not start at defects - the weak points?
I'm sure there's something neater here than I'm seeing; it would be nice if the article had more info.
Now how long till they can whip-up a batch of Ice-Nine and freeze the whole planet?
From the article submission:
And from the actual article itself: Those look pretty similar to me! Given that the article submission is word-for-word exactly from the article itself, it's fair to assume that the submitter, Killer Instinct, is the same person as the author of the article, Robert Roy Britt. How else could the same text be attributed to two supposedly different people?If you're going to submit an article, summarize it in your own words. If you're just going to paste in the first few sentences of the article, attribute them to the proper author by using a phrase such as, "Quoted from the article: 'insert quote here'." Removing line breaks is not enough to satisfy the "summarize in your own words" criteria.
Here's an example of what the submission should've looked like if Slashdot cared at all about given proper attribution for written text:
Source
Dear Cecil:
I have a friend who insists that filling an ice cube tray with warm water will cause the cubes to form more quickly than they would if you started with cold water. He said it had something to do with the air circulation around the trays being affected by the temperature.
Not knowing much about frigidity myself, but being contrary, not to mention skeptical, by nature, I expressed doubt. Cecil, was I right, or is there indeed some basis in fact for this foolishness? --Mary M.Q.C., Santa Barbarba, California
Cecil replies:
You were smart to let me handle this, Mary. God knows what would happen if you tried to experiment with ice cubes on your own.
Needless to say, I conducted my research in the calm and systematic manner that has long been the trademark of Straight Dope Labs. First, I finished off a half a pint of Haagen-Dazs I found in the fridge, in order to keep my brain supplied with vital nutrients.
Then I carefully measured a whole passel of water into the Straight Dope tea kettle and boiled it for about five minutes. This was so I could compare the freezing rate of boiled H20 with that of regular hot water from the tap. (Somehow I had the idea that water that had been boiled would freeze faster.)
Finally I put equal quantities of each type into trays in the freezer, checked the temp (125 degrees Fahrenheit all around), and sat back to wait, timing the process with my brand new Swatch watch, whose precision and smart styling have made it the number one choice of scientists the world over.
I subsequently did the same with two trays of cold water, which had been chilled down to a starting temperature of 38 degrees.
The results? The cold water froze about 10 or 15 minutes faster than the hot water, and there was no detectable difference between the boiled water and the other kind. Another old wives' tale thus emphatically bites the dust. Science marches on.
AN ANOMALOUS SITUATION ARISES
Dear Cecil:
Just a few days after I read your column on whether hot water freezes faster than cold water (you said it didn't), I happened to come across an article in Scientific American entitled "Hot Water Freezes Faster Than Cold Water. Why Does It Do So?" What gives? I hope we will see another column soon resolving the issue. --Ellen C., Chicago
Dear Ellen:
I know it must unnerve you to find that a supposedly infallible source of wisdom can make mistakes, so let me hasten to reassure you: Scientific American did not screw up. My results and theirs (specifically, those of Jearl Walker, author of SA's "Amateur Scientist" column) are consistent--we were just working in different temperature ranges.
I found that cold water (38 degrees Fahrenheit) froze faster than hot water out of the tap (125 degrees F). I chose these two temperatures because (1) they were pretty much what the average amateur ice-cube maker would have readily available and (2) I couldn't find a mercury thermometer that went higher than 125 degrees.
Jearl, who is not afflicted with penny-pinching editors like some of the rest of us, was able to get his mitts on a thermocouple that could measure as high as the boiling point, 212 degrees F. He found that water heated to, say, 195 degrees would freeze three to ten minutes faster than water at 140-175 degrees. (There were differences depending on how much water was used, where the thermocouple was placed, and so on.)
Jearl suggested that the most likely explanation for this was evaporation: when water cools down from near boiling to the freezing point, as much as 16 percent evaporates away, compared to 7 percent for water at 160 degrees. The smaller the amount of water, of course, the faster it freezes.
In addition, the water vapor carries away a certain amount of heat. To test this theory
...smartass slashdotters crack jokes about a new discovery to hide their own insecurities. I, for one, freely admit I have no idea how ice melts.
1+1=2 anyone?
This article is too bad; there's probably an interesting result here, but it appears to be shrouded in vagueness and analogy.
It's true that the *exact* mechanism for melting has not been "seen", but the concepts really are well known. Our models are good enough that computer simulations can be very accurate. I have seen several which show features such as surface melting, for instance.
Also, it is absolutely expected that melting begin at defects, but this does not mean that "melting begins below the melting point" as the article suggests. These areas are locally amorphous and there is no reason that they should begin melting at the crystal's melting point. Really, it's all in the free energy equations.
I'm guessing that the real result has been butchered by the article.
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This is a particularly pervasive myth. Of course, the folklore is incorrect: according to basic thermodynamics, a quantity of warm water will invariably take longer to freeze than an equal quantity of cold water.
Note that key phrase, "an equal quantity" -- in an experiment with two uncovered containers of hot and cold water, you'll find that the resultant mass of water in each of the containers is anything but: a good deal of water from the hot water container is lost to evaporation. So, with a decreased mass, it's easy for the originally hot water to cool more quickly than a significantly larger mass of cold water.
Essentially, hot water does cool faster than cold water in an uncovered container, but you end up with significantly less ice than if it were originally cold.
Is thrilled to know exactly how he will die come spring.
If you could reason with religious people, there would be no religious people
Oh, and don't forget, you can use distilled water to make 2" long ice spikes on your cubes!
Until now, scientists could not explain why ice cubes in your drink melt.
Scientists does not explain why things happen. Only how.
thomasdamgaard.dk.
It is called the Mpemba Effect.
More on this phenomenon (history en possible explanations) here
using hot water makes it faster than using cold water, right?
Water that's really hot will loose heat more rapidly than cool water in the same surroundings. What people don't get is that once the hot water has cooled off, it now cools at the slower rate.
What actually IS useful about freezing hot water is that there are a lot less air bubbles so the ice doesn't crack and throw shards out when you pour freshly brewed tea over it on a hot summer afternoon.
IIRC, the explanation for the ice-cube-trays-in the-freezer 'anomaly' seems to involve the specific temperatures of the two samples, the insulating sides of the tray (minimising heat loss via conduction), enthalpy of vaporisation and the temperature gradient in the water. But don't quote me.
What appears to be a comprehensive exposition on the matter can be found here here.
.:the truth is a lie undiscovered:.
This reminds me of a similar effect that I often observe while cooking, particularly while stir-frying (or any other high-heat method). That is: a drop of water will evaporate more quickly in a pan on medium heat that it will in a pan on high heat.
The reason? When a drop of water hits a pan on very high heat, the underside is instantly tranformed into a layer of vapor which then acts as a buffer between the pan and the liquid on top. So insulated, the water droplet will then "dance" and roll around the pan like a ball bearing. The drop can remain in the pan for a surprising amount of time, though I have never personally measured.
There they were, sitting in the van with all those dials, and the cat was dead. -V. Marchetti, CIA
If "pre-melting" truly begins at the defect sites, it would be interesting to see whether ultra-low defect containing crystals melt at a higher temperature. Say, purify and grow a chunk of ice through the same procedure used to fabricate semiconductor grade silicon (Czochalski style or epitaxially), and then see if it holds together through warmer temps.
You could imagine two closed cylindrical containers, each initially filled with a substance in a liquid state. The liquid of container A is at a temperature such that the density is the minumum. The liquid in container B is initially at a higher temperature than container A. For simplicity's sake, the only extremum of density with respect to temperature is the minimum I mentioned. You begin cooling both liquids at the top of the cylinder.
As heat is transferred from container A, the density will always be increasing from the top to the bottom of the container in a predictable fashion, i.e., the "heavier" substances will always be on the bottom of the container. This doesn't promote convection. With container B, there are good opportunities for convection, due to the varying density gradient and the effect of gravity. Solid forming on the top of container B could even sink. The convection leads to a higher sustained temperature gradient at the cylinder boundary, leading to faster heat transfer and faster cooling.
Note that this mechanism doesn't require an open system. There are, of course, other possible mechanisms, but this is the simplest one I could come up with.
Actually, the original value for freezing in the Centigrade scale was 100 and boiling was zero. It wasn't changed until the mid 1700's.
While what you're saying is true, I think that the way you put it may give people reason to exaggerate the life span of the original scale. The original system was proposed in 1742, and modified to its current version in 1747. Both are years I'd say qualify for the being part of "the mid 1700's".
Reference.
May we live long and die out