A glass of cold milk and a glass of hot milk are placed in the freezer compartment of the refrigerat

Hot milk will freeze first.

The speed of cooling is not determined by the average temperature of the liquid, but by the temperature difference between the upper and lower surfaces of the liquid, when hot milk is cooled, the temperature difference is greater, and the higher the temperature of the upper surface, the more heat is emitted from the surface, so the cooling is faster.

That's an interesting question! Let's ** it.

According to common sense, iced milk is obviously more likely to freeze than hot milk.

This is because when hot milk cools, its molecules slow down their movement and gradually become more orderly. However, when the water molecules in hot milk meet the air in a cold refrigerator, they quickly cool down and form ice crystals. These ice crystals continue to absorb the remaining milk molecules, resulting in the formation of larger ice crystals.

In contrast, the water molecules in ice milk are already at the lowest energy level, so they have reached their maximum order. This means that the water molecules in iced milk are more difficult to crystallize than those in hot milk. In addition, since the temperature of iced milk is lower than that of refrigerator air, water molecules absorb heat from iced milk, which slows down the formation of ice crystals.

To sum up, hot milk will freeze faster than iced milk.

The time required for hot milk ——— iced milk is t1, and the freezing time for iced milk is t2. Because hot milk goes to ice milk first and then to frozen, cold milk is fast, although the book says it is hot fast...

Categories: Life.

Analysis: The hot cup will freeze first.

From the perspective of physics, there are four mechanisms of cooling: radiation, conduction, vaporization, and convection, and it is found through experimental observation that the reason for the freezing of hot water before cold water is mainly the comprehensive result of the interaction of conduction, vaporization, and convection. The glass contains 4 When the cold water freezes, because the water and the glass are poor conductors of heat, the heat inside the liquid is difficult to transfer to the surface by conduction, and the water in the cup gathers on the surface due to the drop in temperature, volume expansion, and density decreases, so it freezes first at the surface of the water, followed by the bottom and all around, thus forming a closed "ice shell".

At this time, the inner layer of water is isolated from the air, and can only be dissipated by conduction and radiation, cooling very slowly, in addition, this "ice shell" plays a "suppression" effect on the volume expansion of water when it freezes, which also slows down the rate of internal icing. The glass with 100 hot water is relatively less frozen, and the phenomenon is that the ice layer on the surface can not be connected into an ice sheet, and the "ice shell" can not be seen, but the needle-like ice crystals grow into the liquid along the ice-water interface (this phenomenon cannot be seen when the initial temperature is lower than 12), and gradually thicken, this is because the hot water at the initial temperature, the cooling density of the upper water becomes larger and flows downward, forming an internal convection of the liquid, so that the water molecules form ice around their respective crystal centers, the higher the initial temperature, the more intense this convection, The greater the energy loss, the faster the rate of cooling, and although the "ice sheet" is formed in the end, the cooling rate becomes smaller, but because the ice crystals in the water have grown and are coarse, with a large surface energy, the rate of ice crystal growth is still much faster than that of water with a low initial temperature.

From the perspective of biological action, microorganisms in water are often the "crystallization centers" where water can freeze. Some microorganisms multiply faster in hot water (below 100) than in cold water, which has many more "crystallization centers" than in cold water, accelerating the synergistic effect of hot water freezing.

The Mpeba effect, where the hot water freezes first.

1.Evaporation – During the process of cooling the hot water to the initial temperature of the cold water, the hot water loses some of its water due to evaporation. Less mass makes water easier to cool and freeze.

This way the hot water may freeze earlier than the cold water, but the amount of ice is less. If we assume that water only loses heat through evaporation, theoretical calculations show that evaporation explains the MPEMBA effect. This explanation is plausible and intuitive, and evaporation is indeed an important factor.

However, this is not the only mechanism. Evaporation cannot be explained by experiments done in a closed vessel where no water vapor can leave. Many scientists claim that evaporation alone is not enough to explain the experiments they have done.

2.Dissolved Gases – Hot water retains fewer dissolved gases than cold water, and as it boils, a large amount of gas escapes from the water. Dissolved gases can change the properties of water.

Either make it easier to form convection (and therefore cooler), or reduce the amount of heat required to freeze per unit mass of water, or change the boiling point. There are some experiments that support this explanation, but not theoretical calculations.

3.Convection – Due to cooling, water forms convection currents and uneven temperature distributions. As the temperature rises, the density of the water decreases, so the surface of the water is hotter than the bottom of the water"Hot top".

If the water loses heat mainly through the surface, then,"Hot top"The water loses heat faster than the temperature is uniform. When the hot water is cooled to the initial temperature of the cold water, it will have a hot top and hence it will cool faster compared to the average temperature but the water with a uniform temperature. Although the thermocap and associated convection can be seen in experiments, it is still unknown whether convection can explain the MPEMBA effect.

4.The things around – the last one of the two glasses of water – have nothing to do with themselves, but with their surroundings. Water with a higher initial temperature may change its surroundings in complex ways, thus affecting the cooling process.

For example, if this glass of water is placed on top of a layer of frost, the frost conducts heat poorly. The hot water may melt this layer of frost and create a better cooling system for itself. Obviously, this explanation is not general, and many experiments do not place the container on the frost layer.

Finally, supercooling may be important for this effect. Supercooling is the phenomenon in which water freezes when it is below 0. There was an experiment that found that hot water is less likely to be supercooled than cold water.

This means that the hot water will freeze first because it freezes at higher temperatures. But this does not explain the MPEMBA effect completely, because we still need to explain why less hot water will be too cold.

In many cases, hot water freezes before cold water, but this phenomenon is not observed in all experiments. And, although there are many explanations, there is still no perfect one. So, the Mpemba effect remains a mystery.

At first glance, our first impression is that of course the cold water freezes fast. But that's not the case. If you put two cups of water of equal weight in the refrigerator, one cold and one hot, they will start to lose heat in the refrigerator at the same time.

Physically, there are four mechanisms of cooling: radiation, conduction, vaporization, and convection.

It would be even more revealing if the process of hot and cold water freezing was described and the causes of it were analyzed

A cup containing cold water with an initial temperature of 4 freezes for a long time, and the water in the cup expands in volume due to the drop in temperature, and the density becomes smaller, and it gathers on the surface. Therefore, the water freezes first at the surface, followed by the bottom and the periphery, which also acts as a constraint or inhibition on further freezing.

The cup containing the initial temperature of 100 hot water has a relatively small freezing time, and the phenomenon seen is that the ice layer on the surface can not be connected into an ice sheet, and the phenomenon of "ice shell" formation cannot be seen, so the hot water freezes first.

There are two possibilities for this problem:

1.When the temperature of the cup of hot water is not very high, about 40 to 50 degrees Celsius, it is obvious that the cold water freezes first.

2.When this is a cup of boiling water, there is a good chance that you will see the hot water freeze first. The process of freezing in the refrigerator is the process of accelerating the loss of heat.

In physics, in general, a substance needs to release heat when it is converted from a liquid state to a solid state, and a cup of hot water has significantly more heat than cold water, so it obviously needs to lose more heat, and the cooling time required will be longer. But it's not the same if it's boiling water. After the water is boiled, the dissolved oxygen and other impurities in it will volatilize, then this glass of water is equivalent to being purified (water in nature has impurities), and the freezing point of pure substances will change, which is different from water in a pure natural state, so you may see the phenomenon that the hot water freezes first.