Children know how to puzzle parents and other adults with questions: “Why is the sky above us blue?”, “Why is the sun shining?”, “Why does the river flow?” ... In winter, a favorite children's question: “Why is the snow white, crunches and creaks underfoot? » And it is worth dealing with this interest right away, since the current winter is not the last, and if you hush up the issue now, then it will face the parents in just a year.
Snow color
Why the snow crunches underfoot, we’ll figure it out a little later, we’ll first decide on the first part of the question. Children who are ripe for it already know that snow is frozen water, that is, ice. Ice is transparent, therefore colorless, so why is snow white?
If you catch a snowflake and look closely at it, it is easy to see that it is also mostly transparent. It acquires color only when its edges reflect light - it doesn't matter whether it is sunny or artificial. And if the snowflakes were neatly stacked, they would seem transparent, except that the edges would be painted - in the color of the sky or the nearest advertising billboard. However, the snow falls randomly, the edges are exposed to the sun at different angles, reflect and refract it, again chaotically. As a result, the eyes perceive a freshly attacked snowdrift as perfectly white (of course, if there is not a cloud in the sky).
When the snow crunches
Now it remains to find out why the snow creaks underfoot. Keeping in mind that snowflakes are ice floes, the answer to this question is not too difficult to give. The ice crystals they are are quite brittle, though hard. With pressure on them (for example, under the mass of a person walking in the snow), the snowflakes are destroyed, making a barely audible crunch. It is accompanied by the same almost (but only almost!) soundless creak from the friction of tiny pieces of ice one against the other. If only one snowflake broke, the human ear would not be able to hear such a small sound. However, there are tens of thousands of them, and even millions - and the crunch with a creak becomes audible. In addition, very thin connections-bridges appear between individual snowflakes in a snowdrift from frost, invisible to the eye, but adding their note to the noise.
When the snow doesn't creak
The offspring are not always satisfied with the answer: either they consider it abstruse, or it does not coincide with their vision of the world. However, the following questions arise much more often, logically arising from your explanations: “Then why does the snow crunch underfoot in frosts, and when it’s not very cold, it doesn’t?” First of all, because snowflakes become more flexible, elastic and do not break immediately under slight cold - many have time to melt under pressure. There is also no friction between individual crystals - it is “lubricated” with water, which does not have time to freeze. And interlayer bridges are also not formed, so there is nothing to burst. Accordingly, the question: “Why does the snow crunch underfoot” will not arise in a child walking nearby. True, only until the next cold snap!
However, parents, who explained why the snow crunches under their feet, and wiped the sweat from their foreheads with relief, should not relax. Very soon, their child will please them with the next question - and who knows how successfully it will be possible to answer it.
Children love to ask different questions, which can be difficult to answer. We have already found out why the fallen snow is white. At first glance, the answer to this question is very simple. But actually it is not. This time we will talk about snow again, we will figure out why it makes a characteristic sound, crunch or creak at sub-zero temperatures.
To answer this question, why the snow crunches underfoot, you first need to understand what it is all about - snow. High above the ground, among the clouds, water freezes and turns into small crystals. These crystals are called snowflakes. They always take the form of a hexagon.
After freezing, they begin their journey to the ground, and in the process, more and more crystals freeze to each of the six corners. This happens randomly for some time, so the probability of finding two identical snowflakes is extremely small. Each snowflake has its own unique size and shape.
Why do snowflakes crunch when stepped on
It's very simple - when the snow is pressed, a lot of crystals break against each other. It is especially interesting that the loudness of the crunch depends on the air temperature - the colder it is, the louder the snowflakes break.
This is because as the temperature drops, the crystals become harder and harder, and they break more easily. There is another hypothesis - the crunch occurs because the snowflakes rub against each other.
But if we pick up and break one snowflake, we will not hear any sound. He is very quiet, and no one in the world can distinguish him. The crunch effect occurs only when a huge number of ice crystals break at once. It is because so many snowflakes are breaking at the same time that we hear this sound.
If the temperature rises, the crystals begin to turn into water, it becomes more difficult to break them, and the sound disappears.
When thinking about winter, a snow-white cover always appears in the imagination, enveloping everything around, and rarely does anyone think about why it is white.
Droplets of water in the atmosphere, at sub-zero temperatures, freeze and turn into ice, falling to the ground in the form of snow. Ice is water in a solid state, it is transparent in itself. Then why is snow white?
Snowflakes also have no color, but if you look at them through a magnifying glass, you can see that they look like crystals, resembling a regular hexagon with edges in their shape. During a snowfall, it is the edges of the snowflakes that reflect the light rays that give the snow its usual white color.
On the ground, snow cover is a cluster of snowflakes located very tightly to each other in a chaotic manner. Together they reflect light with greater force, so even at night, when the surface is not illuminated by the sun, we see snow as white. The source of light rays at night are the moon, stars, lanterns.
However, the reason for the "whiteness" of the snow cover lies not only in the ability of the faces of ice crystals to reflect the light falling on them, but also in the purity of their surface. The bottom line is that no snowflake can be perfectly transparent. In the atmosphere, water droplets mix with various particles (dust, industrial emissions and other pollutants) that are able to absorb unreflected light rays.
Why does snow glitter?
In this case, the well-known law applies: the angle of incidence is equal to the angle of reflection. Billions of microcrystals shaped regular hexagon, absorb the sun's rays, refract them, and then reflect in different directions and at different angles, like "sunbeams". Therefore, we see how snowflakes sparkle and shimmer in the sun.
Why do snowflakes crunch and creak underfoot?
Walking through the snow, you can often hear a crunch or creak under your feet. Such a sound is obtained because the crystals of snowflakes rub against each other under mechanical pressure and break. However, this phenomenon can not always be observed, but only at a certain air temperature.
The fact is that snow creaks only at temperatures from 2 to 20 degrees below zero, and in different temperature ranges, creaking and crunching are accompanied by a special sound. This is explained by the fact that in severe frost, the crystals of snowflakes become denser and stronger, and at a temperature of 0 ° C and above, the snow cover loses its strength and begins to melt.
In fact, even the break of one small snowflake is accompanied by sound. But this sound is so weak that the human hearing organs simply do not perceive it. While trillions of snowflakes are breaking, the sound becomes much stronger and a person can clearly hear the characteristic crackling of snow.
Snow creaks. In very frosty weather, its creak can be heard for several tens of meters. What caused this phenomenon? Why do sounds get louder and weaker as the temperature changes?
It turns out that the creak is a consequence of the special structure of the snow, and when the temperature rises / falls, this structure changes and the sounds are already different.
Snowflakes: education and structure
Snow is “composed” of individual snowflakes - crystalline formations consisting of frozen water (about 5%) and air (about 95%). The composition determines their fragility, lightness and extremely low strength, and the predominant proportion of air -.
Scientists have studied in detail the process of formation of snowflakes. Water that evaporates from the surface of the Earth rises in the form of vapor into the atmosphere, where it cools and concentrates into droplets, forming rain clouds.
With significant cooling, microscopic droplets, in contact with dust particles, freeze, forming six-pointed crystals.
Dust, as well as smoke particles, even insects become the core of crystallization. Snow researcher A. D. Zamorsky tells about a snowflake, in the core of which there was a small midge - a crystal grew around the frozen insect.
The six-pointedness of the main crystal of a snowflake is due to the peculiarity of the water molecule, due to which the angle between the rays can be only 120 ° or 60 °. But each of us, looking at a snowflake, saw how much more complex and beautiful its pattern is than an ordinary hexagon. The patterning is caused by the growth of other crystals on the main beams, with their own angles. 
There are also snowflakes of irregular shape. It was formed due to the constant movement of snow in the air layers, where it either thaws or crystallizes again, building up new rays on the deformed parts.
In the middle of the twentieth century, the Snow and Ice Commission, which is a department International Association scientific hydrology, adopted as the fundamental International Snow Classification. Pundits have divided all the snowflakes into ten large groups. Each could now be defined in one of the classes:
- stars, or dendrites;
- spatial (complex) dendrites;
- irregular crystals;
- plates;
- columns;
- crowned columns;
- hail;
- grains;
In each class, subspecies are distinguished, for example, broken crystals, complex particles from many crystals, particles in frost, and many others. 
The disadvantage of the classification is that it does not take into account the shape of the structure of snow grains in the snow cover, which is even more complex and diverse.
What determines the shape of a snow crystal?
Professor-researcher U. Nakaya, an employee of the University of Hokkaido, has been dealing with this issue all his life. At the beginning of the 20th century, in 1936, in his tiny laboratory, he was the first on earth to obtain an artificial snowflake in terms of appearance.
In memory of the “master of snow”, the Japanese have laid out a park on the territory of the former laboratory, in which a monument has been erected.
The professor found out that the shape of a snow crystal depends on the moisture content in the air and its temperature. So, the most beautiful snowflakes - stars - are formed in a narrow range from -14°С to -17°С.
All data were obtained and repeatedly confirmed by U. Nakaya experimentally. The process has not received a theoretical justification and interpretation and is waiting for its discovery.
Causes of snow squeak (crunch)
It is easy to guess from the previous explanations that the creak of snow is crystals breaking when pressed. When we step on snowflakes, their extremely fragile rays break.
An additional creak and crunch is created by the friction of the crystals against each other. Snow creaks especially loudly in frost - 1000–1600 Hz, when the crystals acquire increased (for them) hardness and brittleness and are deprived of the water lubricant permanently present on their surface - evaporation.
As the temperature rises, the snow melts, evaporation increases, water softens the friction of the crystals, and the snowflakes themselves become less fragile - “soft”. When pressed, they break and crumble. The sound from the destruction of "soft" crystals is in the range of 250-400 Hz. When the temperature rises to -6 ° C and above, the crunch and creak noticeably weaken until they disappear completely. 
If the snow is caked or the snowflakes are melted into a crust, the bonds between them become much stronger, and they are able to crunch even at 0 ° C. True, it looks a little like a creak, rather, a rustle or a specific noise.
Snow is a sign of real winter. It is formed when small raindrops freeze. Fluffy white snow is a real miracle. Children make snowmen out of it, play snowballs with them, and northern peoples build their houses out of snow. A thick layer of snow warms the earth. It does not allow frosty air to reach it, and maintains a positive temperature in the depths of the soil.
What is snow and how is it formed?
In scientific terms, snow is a type of precipitation. This means that snow falls from the sky in the form of frozen rain. Snow is cold, white and fluffy. It consists of individual snowflakes that look like six-pointed stars. I wonder how snow is formed?
The first condition for the appearance of snow is cold. The temperature at which water turns into ice is 0ºC. When it gets cold outside, the water in puddles and lakes becomes covered with ice (freezes). Rain clouds freeze in the sky at this time. Raindrops turn into snow.
The second way snow is formed is scientifically called evaporation. Hear how it goes. If you wash clothes and hang them outside in winter, the wet sheet will first freeze and become hard. After a few days, the sheet will turn into a soft, dry cloth. What happened? First, the water in the sheet turned to ice. It happened pretty quickly. Then the ice began to evaporate: small microscopic pieces of ice broke off the sheet and rose into the sky. These ice floes were so small that, looking at the drying sheet, we did not notice their flight.
Why is it snowing?
Many small ice floes are found in the heavenly heights. There they gather in a snow cloud. There are so many snowflakes in a cloud that they join together in several pieces. A few small ice stars form a large snowflake, which becomes too heavy and falls down. This is how the snow starts.
In order to form a large snow cloud, one wet sheet is not enough. Many tiny pieces of ice rise into the sky from a frozen lake, puddle or river. There they gather in large snow clouds.
The wind can carry such a cloud far. For example, where there is no frost. Thanks to the wind, snow can fall even in places where lakes and rivers have not yet frozen.
How are snowflakes formed?
Have you ever seen a snowflake under a microscope? It looks like a six pointed star. Each end of the asterisk consists of a white branch on which small white twigs grow.
These branches are scientifically called crystals. They intersect in the middle of the snow star. Each snowflake begins to grow from the center - from the place where the snow branches intersect. The growth of a snowflake is similar to the growth of a tree: six trunks grow from the center, on each of which branches begin to grow. Stars can have different branches (long or short, thick or thin), but always only 6 large branches grow in a snow star.
When water in a river or puddle freezes, ice is formed. The stars in the ice are located close to each other. When the fog or cloud freezes, the stars are located at some distance from each other. If there are too many stars, they are connected in several pieces and fall down. So the snow falls out of the clouds and covers the roads, houses and fields. Falling snowflakes adults call snowfall.
Why does the snow creak underfoot?
If there is a slight frost on the street (-2 or -3 ºС), then there is a lot of water in the fallen snow. They say about such snow that it is “wet”. It is easy to make snowballs and a snowman out of wet snow, to build "fortresses".
When the frost gets stronger (the air temperature drops to -5 or -10 ºC), the snow freezes harder and becomes dry. It is impossible to make a snowman out of dry snow, but it creaks loudly underfoot. Why does dry snow creak?
Each snowflake is like a small star. If we step on the snow, the branches in the icy snowflakes break. So when breaking many snowflakes, a crunch and creak is formed.
Snow creaks with any pressure:
- if it was stepped on;
- went on skis;
- rode on sleds.
Snow stops creaking only when it becomes almost warm (air temperature approaches 0ºC). Or when he was heavily rolled (this happens on the hills, where the snow rolls and turns into ice).
When the snow creaks very loudly?
Snow can squeak louder or quieter. When does the crunch of snow get very loud?
This happens in extreme cold. For example, in the far north at -50ºC, the crunch of snow becomes so loud that it can be heard on the next street.
With warming, when the air temperature approaches 0ºC, the crunch disappears completely. Snowflakes become soft, drops of water appear on their icy branches, which prevents the icy stars from creaking.
Scientists conduct curious experiments with frozen water. It turns out that water hears us and reacts differently to gentle and rude words. That's what the next video is about.
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