We have been told since childhood that water freezes and turns into ice at zero degrees. However, science as proved quite the opposite! It has been revealed that pure liquid water freezes at a much lower degree of C becoming super cool! How is this effect explained? The answer will surprise everyone! For water to form ice at the temperature higher than C, it needs a solid particle called nucleator. This particle will initiate water molecules to nucleate and form ice crystals on the surface.
So the science investigations found out that dissolving certain substances in water can change the speed of the nucleation process. The second these elements contact water, they can either speed up or slow down the water molecules to freeze and change into a solid form.
Of course, the correct answer would be that it hangs upon the amount of liquid and the intensity of the heat. The science researches found out that such amount of liquid as one standard cup of water will fully evaporate after 1. The answer is the following. Moving water evaporates faster than still water. It means that when we increase the heat, the molecules start moving faster rubbing against each other which warms the water up after a while. So if we change the heat and make it higher, our liquid will boil sooner.
Also, this is the answer to the question of why water rolls while boiling. As we all know, when water freezes it expands. Science has proved that a long time ago. That is why for freezing this liquid it is best of all to not choose hard tanks or porcelain vessels.
Solidified water can easily damage the surface of the container and even crack it. So, tossing your fitness bottle with water to freeze it is definitely not the best idea! Science is a wonderful thing! You probably asked yourself many times why you find air bubbles packed under the surface inside of the ice cubes, right? In fact, the explanation is simple. The air that is thrown out from the freezing surface becomes erupted right into the ice cube when water freezes.
That is why we often find those floating bubbles inside when taking the ice tray out of the frosting camera. And, how long does it take for snow to melt at 35 degrees? Usually around 5 hours. But it depends on the amount of snow, the thickness of the ice, and is it rainy outside or not. An ordinary 6 inches of snow would melt in about 5 hours. It depends on the temperature in your garage.
I used to freeze a ml bottle of water completely at C, but that was outside. I noticed that water bottles in my garage start freezing slowly. Do you think they can freeze completely? How long does it take for ml of water to freeze? I was once making an experiment and froze 8 inches of water in 72 hours at C. I guess it can, at least, I read somewhere that it is possible to make ice colder than 32 F. Hi everyone!
But what happens when ice keeps on staying frozen? Can ice be colder than 32? How can you make water freeze faster? Yes, water can solidify at 33 or lower. In fact, scientists even found water being frozen at F in the clouds. As far as I remember it from our chemistry lessons, dry ice and ethanol mixed together freeze water immediately. Also, liquid nitrogen works well. Freezing can indeed help to make the water cleaner. Let's forget about the part about magic water that keeps its internal temperature uniform.
That removes the only real physics of the problem, which is thermal diffusion. You've made our life easier by removing gravity, which causes convection, a much mesier process.
So you need the thermal diffusion constant, which is the thermal conductivity divided by the heat capacity per unit volume.
So that's 0. WIth your 1 cm radius, the typical diffusion time is about sec. The exact solution for the time-dependent temperature can be obtained by decomposing the spatial dependence into a bunch of patterns each of which relaxes exponentially toward equilibrium.
The pattern with the longest spatial wiggles has the slowest relaxation. The site you refer to has nice discussions of the limitations of some common explanations of the effect whereby sometimes hot water freezes before cold water.
Unfortunately the explanation they give, that the heat changes the molecular bonds between the water molecules so the resemble those of ice, is pure baloney, far more than the ideas they criticize.
The relaxation time for those little local modes in the water is somewhere crudely in the neighborhood of 10 s, not exactly long enough to help the cooling water remember anything about its past. The main explanation that they leave out is probably the best.
Heating causes dissolved gases to leave the water. Dissolved gasses lower the freezing point. So the heated water has a slightly higher freezing point. We're basically in agreement that various complicated effects can cause hot water to freeze faster than cold under some circumstances. Then the freezing rate is very sensitive to the exact freezing temperature, which depends on dissolved non-water molecules. Typically, hot water has fewer dissolved air molecules than cold water.
That can make the initially hot water freeze before the initially cold water. Another reason can be that more of the hot water evaporates, leaving less behind. The smaller amount left can cool more quickly than a larger amount. These effects can both operate together. You're pointing to another mechanism. That evaporated water gets into very cold air, causing it to condense and then freeze. In effect, the initial heat helped get the water out into better thermal contact with the air, in the form of vapor.
You make a good point in that many experiments are so hard to do that we all have to rely on getting information from others.
This water-freezing-time experiment is really easy to do at home. The home answer will be the one people want. Our results will be different because we'll use a different freezer, different glass, etc. Follow-up on this answer. Learn more physics! Related Questions. Still Curious? How long does it take for water to freeze? Hi Dara! The answer to your question really depends on three things: how much water you have, how cold it is to start out, and how cold the things around it are.
Water actually freezes when it gets to 32 degrees Fahrenheit 0 degrees Celsius , but the time it takes to get there may be different.
Let's start with the first. If you take two glasses, and fill one with a tiny bit of water, and the other about halfway, then put them both in the freezer, the one with less water will freeze first you can try this at home, but I recommend using plastic cups and not glass ones.
Now let's move on to the second part. Let's say you have two glasses, and you fill one with really cold water that has been in the refrigerator, and the other with really hot water from the sink.
If you put both of them in the freezer, the one that started out colder will freeze first. For the third part, let's imagine that you have two glasses with the same amount of water in them, and the water is at the same temperature. Imagine putting one outside on a really really cold day in Georgia, and having a friend in Alaska put one outside on the same day. Since it would be so much colder in Alaska, the glass of water there would freeze before yours.
So, if you took a tiny bit of really cold water in a glass, and put it outside on a cold day in Alaska, it would freeze a lot faster than a big glass of hot water outside on a cold day in Georgia. Hope this helps! It has been known for centuries that hot water freezes faster than cold water.
Both Aristotle and Francis Bean believed this to be true. It has been proven fact in several different experiments by many different scientists. You gave a good answer, and certainly helped out Dara, but I just wanted to make sure she got all her facts straight. Mackenzie- Thanks for your note. You're right to remind us that the common-sense result isn't always right.
Sometimes the hot water freezes faster. I would be a little more cautious than you about authority, however. Aristotle made many mistakes, even on simple questions like how many teeth women have.
Francis Bacon is that who you mean? My own attempts to repeat this experiment have flopped so far. I always forget to look at the glasses until they're both frozen. You might try it yourself, using metal cups so they don't break, and being sure to put the same amount of water in each. Also, try it a few times switching the positions of the hot and cold cups, since freezers don't cool evenly.
The most careful discussions of the subject e. I think Tamara has a good discussion on this site, under the name 'Mpemba effect', named after a high school student who had the courage to believe his observations rather than his teachers.
Mike W. Hot water does not freeze faster than cold water. That idea is ridiculous. It can be misconstrued as such when you look at it without a mind towards physics and chemistry. When a liquid is cooled, it may pass the freezing point and not appear to freeze. This is due simply to the fact that the molecules need additional energy or a solid to begin the crystallization process. In that case the rate of heat flow and therefore freezing would be inversely proportional to the thickness of the skin of ice.
A last complication is that water readily supercools. In case the temperature difference is greater than 40 degrees stefan's law holds good. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Time required for water to freeze Ask Question.
Asked 8 years, 4 months ago. Active 1 year, 11 months ago. Mpemba believed his teacher at the time. But later that year he met a friend of his who made and sold ice cream in Tanga town. His friend told Mpemba that when making ice cream, he put the hot liquids in the refrigerator to make them freeze faster. Mpemba found that other ice cream sellers in Tanga had the same practice.
Later, when in high school, Mpemba learned Newton's law of cooling, that describes how hot bodies are supposed to cool under certain simplifying assumptions. Mpemba asked his teacher why hot milk froze before cold milk when he put them in the freezer. The teacher answered that Mpemba must have been confused. When Mpemba kept arguing, the teacher said "All I can say is that is Mpemba's physics and not the universal physics" and from then on, the teacher and the class would criticize Mpemba's mistakes in mathematics and physics by saying "That is Mpemba's mathematics" or "That is Mpemba's physics.
Earlier, Dr Osborne, a professor of physics, had visited Mpemba's high school. Mpemba had asked him to explain why hot water would freeze before cold water. Dr Osborne said that he could not think of any explanation, but would try the experiment later. When back in his laboratory, he asked a young technician to test Mpemba's claim. The technician later reported that the hot water froze first, and said "But we'll keep on repeating the experiment until we get the right result.
In the same year, in one of the coincidences so common in science, Dr Kell independently wrote a paper on hot water freezing sooner than cold water. Kell showed that if one assumed that the water cooled primarily by evaporation, and maintained a uniform temperature, the hot water would lose enough mass to freeze first [11]. Kell thus argued that the phenomenon then a common urban legend in Canada was real and could be explained by evaporation. But he was unaware of Osborne's experiments, which had measured the mass lost to evaporation and found it insufficient to explain the effect.
Subsequent experiments were done with water in a closed container, eliminating the effects of evaporation, and still found that the hot water froze first [14]. Subsequent discussion of the effect has been inconclusive. While quite a few experiments have replicated the effect [4,6—13] , there has been no consensus on what causes the effect.
The different possible explanations are discussed above. The effect has repeatedly a topic of heated discussion in the "New Scientist", a popular science magazine. The letters have revealed that the effect was known by laypeople around the world long before Today, there is still no well-agreed explanation of the Mpemba effect.
One explanation of the effect is that as the hot water cools, it loses mass to evaporation. With less mass, the liquid has to lose less heat to cool, and so it cools faster. With this explanation, the hot water freezes first, but only because there's less of it to freeze. Calculations done by Kell in [11] showed that if the water cooled solely by evaporation, and maintained a uniform temperature, the warmer water would freeze before the cooler water.
This explanation is solid, intuitive, and undoubtedly contributes to the Mpemba effect in most physical situations. But many people have incorrectly assumed that it is therefore "the" explanation for the Mpemba effect. That is, they assume that the only reason hot water can freeze faster than cold is because of evaporation, and that all experimental results can be explained by the calculations in Kell's article.
But the experiments currently do not bear this belief out. While experiments show evaporation to be important [13] , they do not show that it is the only mechanism behind the Mpemba effect. A number of experimenters have argued that evaporation alone is insufficient to explain their results [5,9,12] ; in particular, the original experiment by Mpemba and Osborne measured the mass lost to evaporation, and found it substantially less that the amount predicted by Kell's calculations [5,9].
And most convincingly, an experiment by Wojciechowski observed the Mpemba effect in a closed container, where no mass was lost to evaporation. Another explanation argues that the dissolved gas usually present in water is expelled from the initially hot water, and that this changes the properties of the water in some way that explains the effect. It has been argued that the lack of dissolved gas may change the ability of the water to conduct heat, or change the amount of heat needed to freeze a unit mass of water, or change the freezing point of the water by some significant amount.
It is certainly true that hot water holds less dissolved gas than cold water, and that boiled water expels most dissolved gas. The question is whether this can significantly affect the properties of water in a way that explains the Mpemba effect.
As far as I know, there is no theoretical work supporting this explanation for the Mpemba effect. Indirect support can be found in two experiments that saw the Mpemba effect in normal water which held dissolved gasses, but failed to see it when using degassed water [10,14].
But an attempt to measure the dependence of the enthalpy of freezing on the initial temperature and gas content of the water was inconclusive [14]. One problem with this explanation is that many experiments pre-boiled both the initially hot and initially cold water, precisely to eliminate the effect of dissolved gasses, and yet they still saw the effect [5,13].
Two somewhat unsystematic experiments found that varying the gas content of the water made no substantial difference to the Mpemba effect [9,12]. It has also been proposed that the Mpemba effect can be explained by the fact that the temperature of the water becomes non-uniform.
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