Research work "Why doesn't ice sink?" Why does ice not sink in water Why does ice float on the surface of water

Polars drift in the ocean ice blocks and icebergs, and even in drinks the ice never sinks to the bottom. We can conclude that ice does not sink in water. Why? If you think about it, this question may seem a little strange, because ice is solid and - intuitively - should be heavier than liquid. Although this statement is true for most substances, water is an exception to the rule. What distinguishes water and ice are hydrogen bonds, which make ice lighter in its solid state than when it is in its liquid state.

Scientific question: why does ice not sink in water?

Let's imagine that we are in a lesson called " The world"in 3rd grade. “Why doesn’t ice sink in water?” the teacher asks the children. And kids, without deep knowledge of physics, begin to reason. “Perhaps this is magic?” - says one of the children.

Indeed, the ice is extremely unusual. There are practically no other natural substances that, in a solid state, could float on the surface of a liquid. This is one of the properties that makes water such an unusual substance and, frankly, it is what changes the path of planetary evolution.

There are some planets that contain huge amounts of liquid hydrocarbons such as ammonia - however, when this material freezes, it sinks to the bottom. The reason why ice does not sink in water is that when water freezes, it expands, and at the same time its density decreases. Interestingly, the expansion of ice can break the stones - the process of glaciation of water is so unusual.

Scientifically speaking, the freezing process establishes rapid weathering cycles and certain chemical substances, released on the surface are capable of dissolving minerals. In general, the freezing of water is associated with the following processes and possibilities: physical properties no other liquids are suggested.

Density of ice and water

Thus, the answer to the question of why ice does not sink in water but floats on the surface is that it has a lower density than liquid - but this is a first-level answer. To better understand, you need to know why ice has low density, why things float in the first place, and how density causes float.

Let's remember the Greek genius Archimedes, who found out that after immersing a certain object in water, the volume of water increases by a number equal to the volume of the immersed object. In other words, if you place a deep dish on the surface of water and then place a heavy object in it, the volume of water that pours into the dish will be exactly equal to the volume of the object. It does not matter whether the object is fully or partially immersed.

Properties of water

Water is an amazing substance that mainly nourishes life on earth, because every living organism needs it. One of the most important properties of water is that it is at its highest density at 4°C. So, hot water or ice are less dense than cold water. Less dense substances float on top of denser substances.

For example, when preparing a salad, you may notice that the oil is on the surface of the vinegar - this can be explained by the fact that it has a lower density. The same law is also valid to explain why ice does not sink in water, but does sink in gasoline and kerosene. It’s just that these two substances have a lower density than ice. So, if you throw an inflatable ball into a pool, it will float on the surface, but if you throw a stone into the water, it will sink to the bottom.

What changes happen to water when it freezes?

The reason why ice does not sink in water is due to hydrogen bonds, which change when water freezes. As you know, water consists of one oxygen atom and two hydrogen atoms. They are attached covalent bonds, which are incredibly strong. However, another type of bond that forms between different molecules, called a hydrogen bond, is weaker. These bonds form because positively charged hydrogen atoms are attracted to the negatively charged oxygen atoms of neighboring water molecules.

When the water is warm, the molecules are very active, move around a lot, and quickly form and break bonds with other water molecules. They have the energy to get closer to each other and move quickly. So why doesn't ice sink in water? Chemistry hides the answer.

Physico-chemistry of ice

As the water temperature drops below 4°C, the kinetic energy of the liquid decreases, so the molecules no longer move. They do not have the energy to move and are as easy as when high temperature, breaking and forming connections. Instead, they form more hydrogen bonds with other water molecules to form hexagonal lattice structures.

They form these structures to keep the negatively charged oxygen molecules away from each other. In the middle of the hexagons formed as a result of the activity of molecules, there is a lot of emptiness.

Ice sinks in water - reasons

Ice is actually 9% less dense than liquid water. Therefore ice takes more space than water. Practically, this makes sense because ice expands. This is why it is not recommended to freeze a glass bottle of water - frozen water can create large cracks even in concrete. If you have a liter bottle of ice and a liter bottle of water, then the bottle with ice water It will be easier. The molecules are further apart at this point than when the substance is in a liquid state. This is why ice does not sink in water.

As ice melts, the stable crystalline structure breaks down and becomes denser. When water warms up to 4°C, it gains energy and the molecules move faster and further. This is why hot water takes up more space than cold water and floats on top of cold water - it is less dense. Remember when you are on the lake while swimming upper layer The water is always pleasant and warm, but when you lower your feet deeper, you feel the cold of the lower layer.

The importance of the freezing process of water in the functioning of the planet

Despite the fact that the question “Why doesn’t ice sink in water?” for grade 3, it is very important to understand why this process occurs and what it means for the planet. Thus, the buoyancy of ice has important consequences for life on Earth. Lakes freeze in cold places during the winter, allowing fish and other aquatic animals to survive under a blanket of ice. If the bottom were frozen, there is a high probability that the entire lake could be frozen.

Under such conditions, not a single organism would remain alive.

If the density of ice were higher than the density of water, then the ice in the oceans would sink, and the ice caps, which in this case would be at the bottom, would not allow anyone to live there. The bottom of the ocean would be full of ice - and what would it all turn into? Among other things, polar ice is important because it reflects light and prevents planet Earth from overheating.

Rice. 4.1. Ice in the water.

As can be seen from Fig. 4.1, the buoyant force is the resultant of water pressure forces acting on the surface of the submerged part of the ice (shaded area in Fig. 4.1). Ice floats on water because the force of gravity pulling it to the bottom is balanced by the buoyant force.
Let's imagine that there is no ice in the glass, and the shaded area in the figure is filled with water. Here there will be no interface between water located within this area and outside it. However, in this case, the buoyant force and the force of gravity acting on the water contained in the shaded area balance each other. Since in both cases discussed above the buoyant force remains unchanged, this means that the force of gravity acting on a piece of ice and on water within the above region is the same. In other words, they have equal weight. It is also true that the mass of ice is equal to the mass of water in the shaded area.
Having melted, the ice will turn into water of the same mass and fill a volume equal to the volume of the shaded area. Therefore, the water level in a glass with water and a piece of ice will not change after the ice melts.
Liquid and solid states.
Now we know that the volume of a piece of ice is greater than the volume occupied by water of equal mass. The ratio of the mass of a substance to the volume it occupies is called the density of the substance. Therefore, the density of ice is less than the density of water. Their numerical values, measured at 0 °C, are: for water - 0.9998, for ice - 0.917 g/cm3. When heated, not only ice, but also other solids reach a certain temperature at which their transition to the liquid state begins. In case of melting pure substance its temperature, when heated, will not begin to increase until its entire mass passes into a liquid state. This temperature is called the melting point of a given substance. Once melting is complete, heating will cause the temperature of the liquid to rise further. If a liquid is cooled, lowering the temperature to the melting point, it will begin to transform into a solid state.
For most substances, unlike the case with ice and water, the density in the solid state is higher than in the liquid state. For example, argon, usually in a gaseous state, solidifies at a temperature of -189.2 °C; the density of solid argon is 1.809 g/cm3 (in the liquid state the density of argon is 1.38 g/cm3). So, if we compare the density of a substance in the solid state at a temperature close to the melting point with its density in the liquid state, it turns out that in the case of argon it decreases by 14.4%, and in the case of sodium - by 2.5%.
The change in the density of a substance upon passing through the melting point for metals is usually small, with the exception of aluminum and gold (0 and 5.3%, respectively). For all these substances, unlike water, the solidification process begins not on the surface, but on the bottom.
There are, however, metals whose density decreases upon transition to the solid state. These include antimony, bismuth, gallium, for which this decrease is, respectively, 0.95, 3.35 and 3.2%. Gallium, whose melting point is -29.8 °C, together with mercury and cesium belongs to the class of fusible metals.
Difference between solid and liquid states of matter.
In the solid state, unlike the liquid state, the molecules that make up the substance are arranged in an orderly manner.

Rice. 4.2. Difference between liquid and solid states of matter

In Fig. Figure 4.2 (right) shows an example of a dense packing of molecules (conventionally depicted in circles), characteristic of a substance in the solid state. Next to it is a disordered structure characteristic of a liquid. In a liquid state, molecules are located at greater distances from each other, have greater freedom of movement, and, as a result, a substance in a liquid state easily changes its shape, that is, it has the property of fluidity.
Fluid substances, as noted above, are characterized by a random arrangement of molecules, but not all substances with such a structure are capable of flow. An example is glass, the molecules of which are arranged randomly, but it does not have fluidity.
Crystalline substances are substances whose molecules are arranged in an orderly manner. In nature, there are substances whose crystals have a characteristic appearance. These include quartz and ice. Hard metals such as iron and lead do not occur in nature in the form of large crystals. However, by studying their surface under a microscope, it is possible to distinguish clusters of small crystals, as can be seen in the photograph (Fig. 4.3).

Rice. 4.3. Microphotograph of the surface of iron.

Exist special methods, making it possible to obtain large crystals of metallic substances.
Whatever the size of the crystals, what they all have in common is an ordered arrangement of molecules. They are also characterized by the existence of a completely definite melting point. This means that the temperature of a melting body does not increase when heated until it completely melts. Glass, unlike crystalline substances, does not have a specific melting point: when heated, it gradually softens and turns into an ordinary liquid. Thus, the melting point corresponds to the temperature at which the ordered arrangement of molecules is destroyed and the crystal structure becomes disordered. In conclusion, we note another interesting property of glass, explained by its lack of a crystalline structure: by applying a long-term tensile force to it, for example, for a period of 10 years, we will be convinced that the glass flows like an ordinary liquid.
Packaging of molecules.
Using X-rays and electron beams, we can study how molecules are arranged in a crystal. X-rays have a much shorter wavelength than visible light, so they can be diffracted by a geometrically regular crystalline structure of atoms or molecules. By recording a diffraction pattern on a photographic plate (Fig. 4.4), it is possible to establish the arrangement of atoms in the crystal. Using the same method for liquids, you can make sure that the molecules in them are arranged in a disorderly manner.

Rice. 4.4. X-ray diffraction by a periodic structure.
Rice. 4.5. Two ways to tightly pack balls.

The molecules of a solid in a crystalline state are arranged in a rather complex manner relative to each other. The structure of substances consisting of atoms or molecules of the same type looks relatively simple, such as the argon crystal shown in Fig. 4.5 (left), where atoms are conventionally designated by balls. You can densely fill a certain amount of space with balls in various ways. Such dense packing is possible due to the presence of intermolecular attractive forces, which tend to arrange the molecules so that the volume they occupy is minimal. However, in reality the structure in Fig. 4.5 (right) does not occur; It is not easy to explain this fact.
So how to imagine various ways Placing balls in space is quite difficult, let's consider how to tightly arrange coins on a plane.

Rice. 4.6. Orderly arrangement of coins on a plane.

In Fig. 4.6 shows two such methods: in the first, each molecule is in contact with four neighboring ones, the centers of which are the vertices of a square with side d, where d is the diameter of the coin; with the second, each coin comes into contact with six neighboring ones. The dotted lines in the figure indicate the area occupied by one coin. In the first case
it is equal to d 2, and again this area is smaller and equal to √3d 2 /2.
The second method of placing coins significantly reduces the gap between them.
Molecule inside a crystal. The purpose of studying crystals is to determine how the molecules are arranged in them. Crystals of metals such as gold, silver, and copper are structured similarly to argon crystals. In the case of metals, we should talk about the ordered arrangement of ions, not molecules. A copper atom, for example, loses one electron and becomes a negatively charged copper ion. Electrons move freely between ions. If the ions are conventionally represented as spheres, we obtain a structure characterized by close packing. Crystals of metals such as sodium and potassium are somewhat different in structure from copper. CO 2 molecules and organic compounds, consisting of different atoms, cannot be represented in the form of balls. When they turn into a solid state, they form an extremely complex crystalline structure.

Rice. 4.7. Dry ice crystal (large large balls - carbon atoms)

In Fig. Figure 4.7 shows crystals of solid CO2, called dry ice. Diamond that is not chemical compound, also has special structure, since chemical bonds are formed between carbon atoms.
Liquid density. Upon transition to the liquid state, the molecular structure of the substance becomes disordered. This process can be accompanied by both a decrease and an increase in the volume occupied by a given substance in space.


Rice. 4.8. Brick models corresponding to the structure of water and solids.

As an illustration, consider what is shown in Fig. 4.8 brick building. Let each brick correspond to one molecule. A brick building destroyed by an earthquake turns into a pile of bricks, the dimensions of which are smaller than the size of the building. However, if all the bricks are neatly stacked one to one, the amount of space they occupy will become even smaller. A similar relationship exists between the density of a substance in the solid and liquid states. Crystals of copper and argon can be matched to the dense packing of bricks shown. The liquid state in them corresponds to a pile of bricks. The transition from solid to liquid under these conditions is accompanied by a decrease in density.
At the same time, the transition from a crystalline structure with large intermolecular distances (which corresponds to a brick building) to a liquid state is accompanied by an increase in density. However, in reality, many crystals retain large intermolecular distances during the transition to the liquid state.
Antimony, bismuth, gallium and other metals, unlike sodium and copper, are not characterized by dense packing. Due to large interatomic distances during the transition to the liquid phase, their density increases.

Ice structure.
A water molecule consists of an oxygen atom and two hydrogen atoms located on opposite sides of it. Unlike a carbon dioxide molecule, in which a carbon atom and two oxygen atoms are located along one straight line, in a water molecule the lines connecting the oxygen atom to each of the hydrogen atoms form an angle of 104.5° with each other. Therefore, there are interaction forces between water molecules that are electrical in nature. Moreover, thanks to special properties hydrogen atom, when water crystallizes, it forms a structure in which each molecule is connected to four neighboring ones. This structure is presented in a simplified manner in Fig. 4.9. Large balls represent oxygen atoms, small black balls represent hydrogen atoms.

Rice. 4.9. Crystal structure of ice.

In this structure, large intermolecular distances are realized. Therefore, when ice melts and the structure collapses, the volume per molecule decreases. This leads to the fact that the density of water is higher than the density of ice and ice can float on water.

Study 1
WHY IS THE DENSITY OF WATER HIGHEST AT 4 °C?

This phenomenon is due to the presence of a crystalline structure in ice. It is shown in Fig. 1 with all the details. 4.10, where for clarity, atoms are depicted as balls, and chemical bonds are indicated by solid lines. A feature of the structure is that the hydrogen atom is always located between two oxygen atoms, being located closer to one of them. Thus, the hydrogen atom promotes the adhesion force between two neighboring water molecules. This adhesive force is called hydrogen bonding. Since hydrogen bonds occur only in certain directions, the arrangement of water molecules in a piece of ice is close to tetrahedral. When ice melts and turns into water, a significant part of the hydrogen bonds are not destroyed, due to which a structure close to tetrahedral with its characteristic large intermolecular distances is preserved. With increasing temperature, the speed of translational and rotational movement of molecules increases, as a result of which hydrogen bonds are broken, the intermolecular distance decreases and the density of water increases.
However, parallel to this process, as the temperature increases, thermal expansion of water occurs, which causes a decrease in its density. The influence of these two factors leads to the fact that the maximum density of water is achieved at 4 °C. At temperatures above 4°C, the factor associated with thermal expansion begins to dominate and the density decreases again.

Study 2
ICE AT LOW TEMPERATURES OR HIGH PRESSURES

By changing temperature and pressure, you can get 13 varieties of ice. The areas of parameter change are shown in the state diagram (Fig. 4.11). From this diagram you can determine which type of ice corresponds to a given temperature and pressure. Solid lines correspond to temperatures and pressures at which two different ice structures coexist. Ice VIII has the highest density of 1.83 g/cm3 among all types of ice.
At a relatively low pressure, 3 kbar, there is ice II, the density of which is also higher than that of water, and is 1.15 g/cm3. It is interesting to note that at a temperature of -120 °C the crystalline structure disappears and the ice turns into a glassy state.
As for water and ice I, the diagram shows that as pressure increases, the melting point decreases. Since the density of water is higher than that of ice, the ice-water transition is accompanied by a decrease in volume, and externally applied pressure only accelerates this process. U ice III, the density of which is higher than that of water, the situation is exactly the opposite - its melting point increases as the pressure increases.

Kim Irina, 4th grade student

Research paper on the topic “Why doesn’t ice sink?”

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Municipal treasury Educational institution"Krasnoyarsk Secondary School"

Research

Performed:

Kim Irina,

4th grade student.

Supervisor:

Ivanova Elena Vladimirovna,

primary school teacher.

With. Krasny Yar 2013

1. Introduction.

2.Main part:

Why do objects float?

Ancient Greek scientist Archimedes.

Archimedes' law.

Experiments.

An important feature of water.

3. Conclusion.

4. List of references.

5. Applications.

Introduction.

Why do some substances sink in water and others not? And why are there so few substances that can float in the air (i.e. fly)? Understanding the laws of buoyancy (and submersion) allows engineers to build ships from metals that are heavier than water, and to design airships and Balloons capable of floating in the air. A life jacket is inflated with air, so it helps a person stay on the water.

No one doubts that ice floats on water; everyone has seen this hundreds of times both on the pond and on the river. But why is this happening? What other objects can float on water? This is what I decided to find out.

Target:

Determining the reasons for the unsinkability of ice.

Tasks:

1. Find out the floating conditions of the bodies.

2. Find out why the ice does not sink.

3. Conduct an experiment to study buoyancy.

Hypothesis:

Perhaps ice does not sink because water is denser than ice.

Main part:

Why do objects float?

If you immerse a body in water, it will displace some water. The body occupies the place where water used to be, and the water level rises.

According to legend, the ancient Greek scientist Archimedes (287 - 212 BC), while in a bath, guessed that a submerged body displaces an equal volume of water. A medieval engraving depicts Archimedes making his discovery. (see Appendix 1)

The force with which water pushes a body immersed in it is called buoyancy force.

Archimedes' law states that the buoyancy force is equal to the weight of the liquid displaced by the body immersed in it. If the buoyancy force less weight body, then it sinks; if it is equal to the weight of the body, it floats.

Experiment No. 1 :(see Appendix 2)

I decided to see how the buoyancy force works, noted the water level, and lowered a plasticine ball with an elastic band into a vessel with water. After diving, the water level rose and the length of the elastic decreased. Marked with a felt-tip pen new level water.

Conclusion: From the water side, a force directed upward acted on the plasticine ball. Therefore, the length of the elastic band has decreased, i.e. the ball immersed in water became lighter.

Then she molded a boat from the same plasticine and carefully lowered it into the water. As you can see, the water has risen even higher. The boat displaced more water than the ball, which means the buoyancy force is greater.

The magic has happened, the sinking material floats to the surface! Hey Archimedes!

To prevent a body from sinking, its density must be less than the density of water.

Don't know what density is? This is the mass of a homogeneous substance per unit volume.

Experiment No. 2: “Dependence of buoyant force on water density”(see Appendix 3)

I took: a glass of clean water(incomplete), a raw egg and salt.

Place an egg in a glass; if the egg is fresh, it will sink to the bottom. Then she began to carefully pour salt into the glass and watched as the egg began to float.

Conclusion: As the density of a liquid increases, the buoyancy force increases.

There is an air pocket in the egg, and when the density of the liquid changes, the egg floats to the surface like a submarine.

Previously, before the invention of refrigerators, our ancestors checked whether an egg was fresh or not: fresh eggs drowning in clean water, and spoiled ones float up, as gas forms inside them.

Experiment No. 3 “Waterfloating Lemon”(see Appendix 4)

I filled a container with water and put a lemon in it. Lemon floats. And then she peeled it and put it back into the water. Lemon drowned.

Conclusion: the lemon sank because its density increased. The lemon's peel is less dense than its interior and contains many air particles that help the lemon to remain on the surface of the water.

Experiment No. 4 (see Appendix 5)

1. I poured water into a glass and put it outside. When the water froze, the glass burst. Place the formed ice in a container with cold water and saw that he was swimming.

2. In another container, salt the water thoroughly and stir until it is completely dissolved. I took ice and repeated the experiment. Ice floats, and even better than in fresh water, almost half protruding from the water.

All clear! An ice cube floats because when it freezes, ice expands and becomes lighter than water. The density of ordinary liquid water is slightly greater than the density of frozen water, that is, ice. As the density of the liquid increases, the buoyancy force increases.

Scientific facts:

1 fact Archimedes: any body immersed in a liquid is subject to a buoyant force.

Fact 2 Mikhail Lomonosov:

Ice does not sink because it has a density of 920 kg/cub.m. And water, which is denser, is 1000 kg/cub.m.

Conclusion:

I found 2 reasons for the unsinkability of ice:

1. Any body immersed in water is subject to a buoyant force.
2. The density of ice is less than the density of any water.

Let's try to imagine what the world would look like if water had normal properties and ice was, as any normal substance should be, denser than liquid water.

In winter, denser ice freezing from above would sink into the water, continuously sinking to the bottom of the reservoir. In summer, the ice, protected by a layer of cold water, could not melt.

Gradually, all lakes, ponds, rivers, streams would freeze completely, turning into giant blocks of ice. Finally, the seas would freeze, followed by the oceans. Our beautiful blooming green World would become a continuous ice desert, covered in some places with a thin layer of melt water. One of the unique properties of water is its ability to expand when freezing. After all, when all substances freeze, that is, during the transition from a liquid to a solid state, they compress, but water, on the contrary, expands. Its volume increases by 9%. But when ice forms on the surface of the water, it, being between the cold air and water, prevents further cooling and freezing of water bodies. This unusual property of water, by the way, is also important for the formation of soil in the mountains. Getting into small cracks that are always found in stones, rainwater expands when freezing and destroys the stone. Thus, gradually the stone surface becomes capable of sheltering plants, which, with their roots, complete this process of destruction of stones and lead to the formation of soil on the mountain slopes.

Ice is always on the surface of the water and serves as a real heat insulator. That is, the water underneath does not cool as much; the ice coat reliably protects it from frost. That is why it is rare that a body of water freezes to the bottom in winter, although this is possible at extreme air temperatures.

The sudden increase in volume when water changes into ice is an important feature of water. This feature must often be taken into account in practical life. If you leave a barrel of water in the cold, the water will freeze and burst the barrel. For the same reason, you should not leave water in the radiator of a car parked in a cold garage. IN very coldy you need to be wary of the slightest interruption in the supply of warm water through water heating pipes: water that has stopped in the outer pipe can quickly freeze, and then the pipe will burst.

Yes, a log, no matter how big it is, does not sink in water. The secret of this phenomenon is that the density of wood is less than the density of water.

By the way...

There are trees that drown in water! The reason for this is that their density is greater than the density of water. These trees are called "iron" trees. “Iron trees” include, for example, Persian parrotia, azobe (African tropical iron tree), Amazonian wood, ebony, rosewood, or rosewood, kumaru and others. All these trees have very hard and dense wood, rich in oils; the bark of these trees is resistant to rotting. Therefore, a boat made of such wood will immediately sink to the bottom, but “iron trees” are an excellent material for making furniture.

In the seas and oceans there are sometimes huge ice mountains- icebergs. These are glaciers that have slid down from the polar mountains and been carried by the current and wind into the open sea. Their height can reach 200 meters, and their volume can reach several million cubic meters. Nine-tenths of the iceberg's total mass is hidden under water. Therefore, meeting him is very dangerous. If the ship does not notice the moving ice giant in time, it may suffer serious damage or even die in a collision.

Rice. 4. Nine-tenths of the iceberg's mass is under water.

Even though the ship is made of iron, very heavy, and even carries people and cargo, it does not sink. Why? But the whole point is that in the ship, in addition to the crew, passengers, and cargo, there is air. And air is much lighter than water. The ship is designed in such a way that there is some space inside it filled with air. It is this that supports the ship on the surface of the water and prevents it from sinking.

Submarines

Submarines sink and surface, changing their relative density. They have large containers on board - ballast tanks. When air leaves them and water is pumped in, the density of the boat increases and it sinks. To float to the surface, the crew removes water from the tanks and pumps air into it. The density decreases again and the boat floats to the surface. Ballast tanks are placed between the outer hull and the walls of the inner compartment. The crew lives and works in the internal compartment. Submarine equipped with powerful propellers that allow it to move through the water. Some boats have nuclear reactors.

Conclusion.

So, after doing a lot of work, I understood. That my hypothesis about why ice doesn’t sink was confirmed.

Reasons for unsinkability ice:

1. Ice consists of water crystals with air between them. Therefore, the density of ice is less than the density of water.

2. A buoyant force acts on ice from the side of water.

If water were a normal liquid and not a unique liquid, we would not enjoy skating. We're not rolling on glass, are we? But it is much smoother and more attractive than ice. But glass is a material on which skates will not slide. But on ice, not even very good good quality Skating is a pleasure. You will ask why? The fact is that the weight of our body presses on the very thin blade of the skate, which exerts strong pressure on the ice. As a result of this pressure from the skate, the ice begins to melt, forming a thin film of water on which the skate glides perfectly.

Application

Annex 1

2015-03-27
Warm water, cooling, becomes denser and, therefore, sinks to the bottom. That is, ice should form at the bottom of the lake first. But this process occurs only up to 4 degrees Celsius, then the water begins to expand again and becomes less dense. Thus, at a point close to freezing, cold water floats to the surface and warm water sinks to the bottom. Eventually, the water at the top of the lake in winter conditions will freeze and turn into a layer of ice. Additionally, when water freezes and turns into ice, the ice becomes significantly less dense than water and continues to float on the surface of the lake.

Ice has a lower density than water due to the fact that it has a hexagonal crystal structure. Each water molecule consists of two hydrogen atoms bonded to an oxygen atom. When ice forms, the hydrogen atoms of one molecule form weak hydrogen bonds with the oxygen atoms of the other two water molecules. The aligned water molecules in this model take up more space than the chaotically mixed molecules in liquid water. Therefore, the ice is less dense. For the same reason, water below 4 degrees Celsius becomes less and less dense.

So now we understand why ice floats on the surface of water, but how does it work on bodies of water? Imagine that it is the beginning of winter and the temperature has only recently dropped below freezing. Air changes temperature faster than water - which is why water in a body of water appears to be much warmer in the evening. The air cools at night, but the water in the reservoir remains almost as hot. Thus, although the air is cold, the water does not freeze. The water in the upper part of the reservoir is in direct contact with cold air and cools all the time. The ice that forms on the surface also acts as a barrier, or insulator, between the cold air and warm water under him.

The latter fact allows the water in lakes and ponds not to freeze to the very bottom, which allows plants and fish to survive the winter in northern conditions.

Why does ice float

Everyone knows that ice does not sink, but floats on the surface of the water. This fact is very unusual, since ice is a solid, and solids, as a rule, always sink in the liquid that is formed when they melt.

All substances in nature expand when heated and contract when cooled. Water follows this rule, but only up to a certain temperature. It contracts, cooling to +4°C. At this temperature, water has the greatest density and weight. As it cools further and turns into ice at 0°C, it... expands. At the same time, the ice increases in volume, and its density and weight decrease. Ice becomes lighter than the water from which it was formed. This is why ice does not melt in water, but floats on its surface.

Thanks to this feature of ice, water in reservoirs freezes only on the surface. If ice sank in water, it would sink to the bottom, the water on the surface would turn into ice again and sink again...in a matter of days, the reservoir would freeze from surface to bottom, and all animals and plants would freeze along with the water... The fact that ice is lighter than water was “invented” by nature so that life in water would not cease to exist, and with it life all over the Earth.

When water freezes and turns into ice, it expands and increases in volume not by any amount, but by about one-ninth. This means that if 9 liters of water freeze, you will get 10 liters of ice.

When the ice floats, we see only one-ninth of it on the surface. For example, if an ice floe has a height of 2 cm above the water, then under water its layer is 9 times thicker, that is, 2 times 9 = 18 cm, and the thickness of the entire ice floe is 20 cm.

In the seas and oceans there are sometimes huge ice mountains - icebergs. These are glaciers that have slid down from the polar mountains and been carried by the current and wind into the open sea. Their height can reach 200 meters, and their volume can reach several million cubic meters. Nine-tenths of the iceberg's total mass is hidden under water. Therefore, meeting him is very dangerous. If the ship does not notice the moving ice giant in time, it may suffer serious damage or even die in a collision.