Why don't ice floes sink in water. Research work "Why doesn't ice sink?". Guarantor of stable air temperature

Ice and water.
It is known that a piece of ice placed in a glass of water does not sink. This is because a buoyant force acts on the ice from the side of the water.

Rice. 4.1. Ice in the water.

As can be seen from fig. 4.1, the buoyancy force is the resultant of the water pressure forces acting on the surface of the part of the ice submerged under water (the 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.
Imagine that there is no ice in the glass, and the area shaded in the figure is filled with water. Here, there will be no dividing line between the water that is within this area and outside it. However, even in this case, the buoyant force and gravity acting on the water contained in the shaded area balance each other. Since in both cases considered above the buoyancy force remains unchanged, this means that the force of gravity acting on a piece of ice and on water within the above area is the same. In other words, they have equal weight. It is also correct 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 will fill the volume equal to the volume of the shaded area. Therefore, the level of water in a glass of water and a piece of ice after the ice has melted will not change.
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. Not only ice, but also other solids, when heated, reach a certain temperature, at which their transition to a liquid state begins. In the case of the melting of a pure substance, its temperature will not begin to rise when heated until its entire mass has passed into a liquid state. This temperature is called the melting point of the substance. After the melting has ended, heating will lead to a further increase in the temperature of the liquid. If the liquid is cooled, lowering the temperature to the melting point, it will begin to go 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, which is 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 when 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 process of solidification does not begin at the surface, but at the bottom.
There are, however, metals whose density decreases during the 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 low-melting metals.
Difference between solid and liquid states of matter.
In the solid state, in contrast to the liquid state, the molecules that make up the substance are arranged in an orderly manner.

Rice. 4.2. The difference between liquid and solid states of matter

On fig. 4.2 (on the right) shows an example of a dense packing of molecules (conditionally depicted by circles), which is characteristic of a substance in the solid state. The disordered structure characteristic of a liquid is shown next to it. In the liquid state, the molecules are at great distances from each other, have greater freedom of movement, and, as a result, the substance in the liquid state easily changes its shape, that is, it has such a property as fluidity.
For fluid substances, as noted above, a random arrangement of molecules is characteristic, but not all substances with such a structure are capable of flowing. An example is glass, whose molecules are arranged randomly, but it does not flow.
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 naturally in large crystals. However, studying their surface under a microscope, one can distinguish clusters of small crystals, as can be seen in the photograph (Fig. 4.3).

Rice. 4.3. Micrograph of iron surface.

There are special methods to obtain large crystals of metallic substances.
Whatever the size of the crystals, they have in common an ordered arrangement of molecules. They are also characterized by the existence of a very definite melting point. This means that the temperature of a melting body does not increase when heated until it is completely melted. 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, due to 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 make sure that glass flows like an ordinary liquid.
Molecule packaging.
Using X-rays and an electron beam, one can study how molecules are arranged in a crystal. X-ray radiation has a much shorter wavelength than visible light, so it can be diffracted by the geometrically regular crystal structure of atoms or molecules. By registering a diffraction pattern on a photographic plate (Fig. 4.4), it is possible to establish the arrangement of atoms in a crystal. Using the same method for liquids, one can verify that the molecules in the liquid are not arranged in order.

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

Molecules of a solid, which is in a crystalline state, are quite complex relative to each other. The structure of substances consisting of atoms or molecules of the same type looks relatively simple, as, for example, the argon crystal shown in Fig. 4.5 (left), where atoms are conventionally designated by balls. You can fill a certain amount of space tightly with balls in various ways. Such dense packing is possible due to the presence of intermolecular attraction 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.
Since it is quite difficult to imagine different ways of placing balls in space, let's consider how you can tightly arrange coins on a plane.

Rice. 4.6. An ordered arrangement of coins on a plane.

On fig. 4.6 two such methods are presented: in the first one, 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; in the second case, each coin is in contact with six neighboring ones. The dotted lines in the figure limit 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 way of placing coins significantly reduces the gap between them.
Molecule inside a crystal. The purpose of the study of crystals is to establish how the molecules are arranged in them. Crystals of metals such as gold, silver, copper are arranged like crystals of argon. In the case of metals, one should speak of an ordered arrangement of ions, not molecules. A copper atom, for example, losing one electron, turns into a negatively charged copper ion. The electrons are free to move between the ions. If the ions are conditionally represented in the form of balls, we obtain a structure characterized by close packing. Crystals of metals such as sodium and potassium differ somewhat in structure from copper. Molecules of CO 2 and organic compounds, consisting of different atoms, cannot be represented in the form of balls. Passing into the solid state, they form an extremely complex crystalline structure.

Rice. 4.7. Crystal "dry ice" (large large balls - carbon atoms)

On fig. Figure 4.7 shows solid CO2 crystals called dry ice. Diamond, which is not a chemical compound, also has a special structure, since chemical bonds form between carbon atoms.
Liquid density. Upon transition to a liquid state, the molecular structure of a 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. Models made of bricks, corresponding to the structure of water and a solid body.

As an illustration, consider the one 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 those of the building. However, if all the bricks are neatly stacked one by one, the amount of space they occupy will become even smaller. A similar relationship exists between the density of matter in solid and liquid states. Crystals of copper and argon can be associated with the depicted dense packing of bricks. The liquid state in them corresponds to a pile of bricks. The transition from a solid to a liquid state 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.
For antimony, bismuth, gallium and other metals, in contrast to sodium and copper, dense packing is not typical. Due to the large interatomic distances, their density increases during the transition to the liquid phase.

Ice structure.
The water molecule consists of an oxygen atom and two hydrogen atoms located on opposite sides of it. Unlike the carbon dioxide molecule, in which the carbon atom and two oxygen atoms are located along one straight line, in the water molecule, the lines connecting the oxygen atom with each of the hydrogen atoms form an angle of 104.5 ° between them. Therefore, there are interaction forces between water molecules that are electrical in nature. In addition, due to the special properties of the hydrogen atom, during crystallization, water forms a structure in which each molecule is associated with four neighboring ones. This structure is simplified in Fig. 4.9. Large balls represent oxygen atoms, small black balls represent hydrogen atoms.

Rice. 4.9. Crystal structure of ice.

Large intermolecular distances are realized in this structure. So when the 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?

Hydrogen bonding and thermal expansion. After melting, the ice turns into water, the density of which is higher than that of ice. With a further increase in water temperature, its density increases until the temperature reaches 4 °C. If at 0°C the density of water is 0.99984 g/cm3, then at 4°C it is 0.99997 g/cm3. A further increase in temperature causes a decrease in density and at 8°C it will again have the same value as at 0°C.

Rice. 4.10. The crystalline structure of ice (large balls are oxygen atoms).

This phenomenon is associated with the presence of a crystalline structure in ice. All details are shown in Fig. 4.10, where, for clarity, atoms are shown 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 closer to one of them. Thus, the hydrogen atom contributes to the emergence of a cohesive force between two adjacent water molecules. This bonding force is called a hydrogen bond. Since hydrogen bonds only occur in certain directions, the arrangement of water molecules in a piece of ice is close to tetrahedral. When ice, having melted, turns into water, a significant part of the hydrogen bonds are not destroyed, due to which the structure is preserved, close to tetrahedral with large intermolecular distances characteristic of it. As the temperature rises, the rate of translational and rotational motion of molecules increases, as a result of which hydrogen bonds are broken, the intermolecular distance decreases and the density of water increases.
However, in parallel with this process, with an increase in temperature, 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 reached at 4 °C. At temperatures above 4°C, the factor associated with thermal expansion begins to predominate and the density decreases again.

Study 2
ICE AT LOW TEMPERATURES OR HIGH PRESSURES

Varieties of ice. Since the intermolecular distances increase during the crystallization of water, the density of ice is less than the density of water. If a piece of ice is subjected to high pressure, the intermolecular distance can be expected to decrease. Indeed, by subjecting ice at 0°C to a pressure of 14 kbar (1 kbar = 987 atm), we obtain ice with a different crystal structure, the density of which is 1.38 g/cm3. If water under such pressure is cooled at a certain temperature, it will begin to
crystallize. Since the density of such ice is higher than that of water, the crystals cannot stay on its surface and sink to the bottom. Thus, the water in the vessel crystallizes starting from the bottom. This type of ice is called ice VI; regular ice - ice I.
At a pressure of 25 kbar and a temperature of 100 °C, water solidifies, turning into ice VII with a density of 1.57 g/cm3.

Rice. 4.11. Water state diagram.

By changing the temperature and pressure, 13 varieties of ice can be obtained. 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. The 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, ice II exists, 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 crystal structure disappears and the ice passes into a glassy state.
As for water and ice I, it can be seen from the diagram that as the pressure increases, the melting point decreases. Since the density of water is higher than that of ice, the transition "ice - water" is accompanied by a decrease in volume, and pressure applied from outside only accelerates this process. For ice III, whose density is higher than that of water, the situation is exactly the opposite - its melting point increases with increasing pressure.

Polar ice blocks and icebergs drift in the ocean, and even in drinks the ice never sinks to the bottom. It can be concluded that ice does not sink in water. Why? If you think about it, this question might seem a little strange, because ice is solid and - intuitively - should be heavier than liquid. While this statement is true for most substances, water is the exception to the rule. Water and ice are distinguished by hydrogen bonds, which make ice lighter in the solid state than when it is in the liquid state.

Scientific question: why ice does not sink in water

Imagine that we are in a lesson called "The World Around" in 3rd grade. “Why doesn’t ice sink in water?” the teacher asks the children. And the kids, not having deep knowledge in 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 the solid state, could float on the surface of a liquid. This is one of the properties that makes water such an unusual substance and, to be honest, it is this that changes the path of planetary evolution.

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

Scientifically speaking, the freezing process sets up rapid cycles of weathering and certain chemicals released at the surface are capable of dissolving minerals. In general, there are processes and possibilities associated with the freezing of water that the physical properties of other liquids do not imply.

Density of ice and water

So the answer to the question of why ice doesn't sink in water, but floats on the surface, is that it has a lower density than liquid—but that's a first-level answer. To better understand, you need to know why ice has low density, why things float in the first place, how density leads to floating.

Recall 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 the water and then place a heavy object in it, the volume of water that will be poured into the dish will be exactly equal to the volume of the object. It doesn't matter if the object is fully or partially submerged.

Water properties

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

For example, while 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 for explaining why ice does not sink in water, but sinks 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 the 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 ice doesn't sink in water is because of the hydrogen bonds that change when water freezes. As you know, water consists of one oxygen atom and two hydrogen atoms. They are attached by covalent bonds that are incredibly strong. However, the other type of bond that forms between different molecules, called a hydrogen bond, is weaker. These bonds form because the 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, quickly form and break bonds with other water molecules. They have the energy to approach each other and move quickly. So why doesn't ice sink in water? Chemistry hides the answer.

Physical chemistry of ice

As the temperature of the water 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 at high temperature to break and form bonds. 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 apart. 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 up more space than water. Practically, this makes sense because the 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 an ice water bottle will be easier. The molecules are farther apart at this point than when the substance is in the liquid state. This is why ice does not sink in water.

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

The importance of the process of freezing 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 is happening and what it means for the planet. Thus, the buoyancy of ice has important implications for life on Earth. Lakes freeze in winter in cold places - this allows fish and other aquatic animals to survive under the ice sheet. If the bottom were frozen, then there is a high probability that the entire lake could be frozen.

In such conditions, not a single organism would have survived.

If the density of ice were higher than the density of water, then the ice would sink in the oceans, and the ice caps, which would then 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 keeps planet Earth from getting too hot.

Everyone knows that ice is frozen water, or rather, it is in a solid state of aggregation. But Why does ice not sink in water, but float on its surface?

Water is an unusual substance with rare, even anomalous properties. In nature, most substances expand when heated and contract when cooled. For example, mercury in a thermometer rises through a narrow tube and shows an increase in temperature. Because mercury freezes at -39°C, it is not suitable for thermometers used in harsh environments.

Water also expands when heated and contracts when cooled. However, in the cooling range from about +4 ºС to 0 ºС, it expands. This is why water pipes can burst in winter if the water in them froze and large masses of ice formed. The pressure of ice on the walls of the pipe is enough to break them.

water expansion

Since water expands as it cools, the density of ice (i.e. its solid form) is less than that of water in its liquid state. In other words, a given volume of ice weighs less than the same volume of water. The foregoing is reflected by the formula m = ρV, where V is the volume of the body, m is the mass of the body, ρ is the density of the substance. There is an inversely proportional relationship between density and volume (V = m / ρ), i.e. with an increase in volume (when water is cooled), the same mass will have a lower density. This property of water leads to the formation of ice on the surface of reservoirs - ponds and lakes.

Let's assume that the density of water is 1. Then the ice will have a density of 0.91. Thanks to this figure, we can find out the thickness of the ice floe that floats on the water. For example, if an ice floe has a height of 2 cm above the water, then we can conclude that its underwater layer is 9 times thicker (i.e. 18 cm), and the thickness of the entire ice floe is 20 cm.

In the area of the North and South Poles of the Earth, water freezes and forms icebergs. Some of these floating ice mountains are enormous. The largest iceberg known to man is considered to be with a surface area of 31,000 square meters. kilometers, which was discovered in 1956 in the Pacific Ocean.

How does solid water increase its volume? By changing its structure. Scientists have proven that ice has an openwork structure with cavities and voids, which, when melted, are filled with water molecules.

Experience shows that the freezing point of water decreases with increasing pressure by about one degree for every 130 atmospheres.

It is known that in the oceans at great depths, the water temperature is below 0 ºС, and yet it does not freeze. This is explained by the pressure that creates the upper layers of water. A layer of water one kilometer thick presses with a force of about 100 atmospheres.

Comparison of the density of water and ice

Can the density of water be less than the density of ice, and does this mean that it will sink in it? The answer to this question is in the affirmative, which is easy to prove by the following experiment.

Let's take from the freezer, where the temperature is -5 ºС, a piece of ice the size of a third of a glass or a little more. Let's put it in a bucket with water at a temperature of +20 ºС. What are we seeing? Ice quickly sinks and sinks, gradually starting to melt. This is because water at a temperature of +20 ºС has a lower density compared to ice at a temperature of -5 ºС.

There are modifications of ice (at high temperatures and pressures), which, due to their greater density, will sink in water. We are talking about the so-called "heavy" ice - deuterium and tritium (saturated with heavy and superheavy hydrogen). Despite the presence of the same voids as in protium ice, it will sink in water. In contrast to "heavy" ice, protium ice is devoid of heavy isotopes of hydrogen and contains 16 milligrams of calcium per liter of liquid. The process of its preparation involves purification from harmful impurities by 80%, due to which protium water is considered the most optimal for human life.

Value in nature

The fact that ice floats on the surface of bodies of water plays an important role in nature. If the water did not have this property and the ice sank to the bottom, this would lead to freezing of the entire reservoir and, as a result, the death of the living organisms inhabiting it.

When a cold snap sets in, at first, at a temperature above +4 ºС, colder water from the surface of the reservoir goes down, and warm (lighter) goes up. This process is called vertical circulation (mixing) of water. When +4 ºС is established in the entire reservoir, this process stops, since from the surface the water already at +3 ºС becomes lighter than the one below. There is an expansion of water (its volume increases by approximately 10%) and a decrease in its density. As a consequence of the fact that the colder layer is on top, water freezes on the surface and the appearance of an ice cover. Due to its crystalline structure, ice has poor thermal conductivity, i.e., it retains heat. The ice layer acts as a kind of heat insulator. And the water under the ice retains its heat. Due to the heat-insulating properties of ice, the transfer of "cold" to the lower layers of water is sharply reduced. Therefore, at the bottom of the reservoir almost always remains at least a thin layer of water, which is extremely important for the life of its inhabitants.

Thus, +4 ºС - the temperature of the maximum density of water - this is the temperature of survival of living organisms in the reservoir.

Application in everyday life

It was mentioned above about the possibility of rupture of water pipes when water freezes. In order to avoid damage to the water supply at low temperatures, interruptions in the supply of warm water that goes through the heating pipes should not be allowed. A motor vehicle is exposed to a similar danger if water is left in the radiator in cold weather.

Now let's talk about the pleasant side of the unique properties of water. Ice skating is great fun for kids and adults. Have you ever wondered why ice is so slippery? For example, glass is also slippery, moreover, it is smoother and more attractive than ice. But skates don't slide on it. Only ice has such a specific delicious property.

The fact is that under the weight of our weight there is pressure on the thin blade of the skate, which, in turn, causes pressure on the ice and its melting. In this case, a thin film of water is formed, on which the steel blade of the skate slides.

Freezing difference between wax and water

As experiments show, the surface of the ice cube forms a kind of bulge. This is due to the fact that freezing in its middle occurs last. And expanding during the transition to a solid state, this bulge rises even more. This can be countered by the solidification of wax, which, on the contrary, forms a depression. This is due to the fact that the wax after the transition to a solid state is compressed. Liquids that contract evenly when frozen form a slightly concave surface.

To freeze water, it is not enough to cool it to the freezing point of 0 ºС; it is necessary to maintain this temperature by constant cooling.

Water mixed with salt

Adding table salt to water lowers its freezing point. It is for this reason that roads are sprinkled with salt in winter. Salt water freezes at -8 °C and below, so until the temperature drops to at least this point, freezing does not occur.

An ice-salt mixture is sometimes used as a "cooling mixture" for low-temperature experiments. When ice melts, it absorbs the latent heat required for transformation from its environment, thereby cooling it. This absorbs so much heat that the temperature can drop below -15 °C.

Universal solvent

Pure water (molecular formula H 2 0) has no color, no taste, no smell. The water molecule is made up of hydrogen and oxygen. When other substances (soluble and insoluble in water) get into the water, it is polluted, so there is no absolutely pure water in nature. All substances that occur in nature can be dissolved in water to varying degrees. This is determined by their unique properties - solubility in water. Therefore, water is considered the "universal solvent".

Guarantor of stable air temperature

Water heats up slowly due to its high heat capacity, but, nevertheless, the cooling process is much slower. This makes it possible to accumulate heat in the oceans and seas in the summer. The release of heat occurs in winter, due to which there is no sharp drop in air temperature on the territory of our planet throughout the year. Oceans and seas are the original and natural accumulator of heat on the territory of the Earth.

Surface tension

Conclusion

The fact that ice does not sink, but floats on the surface, is explained by its lower density compared to water (the specific gravity of water is 1000 kg/m³, of ice is about 917 kg/m³). This thesis is true not only for ice, but also for any other physical body. For example, the density of a paper boat or an autumn leaf is much lower than the density of water, which ensures their buoyancy.

However, the property of water to have a lower density in the solid state is a great rarity in nature, an exception to the general rule. Only metal and cast iron (an alloy of iron metal and non-metal carbon) have similar properties.

Scientific question: why ice does not sink in water

Density of ice and water

Water properties

What changes happen to water when it freezes

Physical chemistry of ice

They form these structures to keep the negatively charged oxygen molecules apart. 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

The significance of the process 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 is happening and what it means for the planet. Thus, the buoyancy of ice has important implications for life on Earth. in cold places in winter - this allows fish and other aquatic animals to survive under the ice sheet. If the bottom were frozen, then there is a high probability that the entire lake could be frozen.

In such conditions, not a single organism would have survived.

Municipal educational autonomous institution

secondary school with. Vasilievki

Research work

Why doesn't ice sink in water?

Pupils of the 3rd "b" class

Belogubova Sofia

Leader: Klimenko

Lyudmila Sergeevna,

teacherIqualifying

The content of the work.

1. Introduction……………………………………………………………. 3

2.Main part:……………………………………………………...4-6

2.1. Why do objects float? .....

2.2. Ancient Greek scientist Archimedes……………………………………

2.3. Law of Archimedes…………………………………………………………….

2.4. Experiments……………………………………………………………..

2.5. An important feature of water…………………………………………...

3. Conclusion………………………………………………………….7

4. References……………………………………………………8

5. Applications……………………………………………………………9-10

Introduction.

Doesn't burn in fire

Doesn't sink in water.

Relevance of the topic

Why do some substances sink in water and others do not? Understanding the laws of buoyancy allows engineers to build ships out of metals that float and don't sink.

There is no doubt that ice floats on water; everyone has seen it hundreds of times both on the pond and on the river.

But why is this happening?

What other items can float on water?

This is what I decided to find out.

Set a goal:

Determine the reasons for the unsinkability of ice.

Set out a number of tasks:

Find out the conditions for floating bodies;

Find out why the ice does not sink;

Conduct an experiment to study buoyancy.

Put forward a hypothesis:

Maybe ice doesn't sink because water is denser than ice.

Research methods:

Theoretical analysis of literature;

Method of observation;

practical method.

Practical material will be useful to me in the lessons of reading, the world around.

Main part

If a body is immersed in water, it will displace some of the water. The body takes the place where there used to be water, and the water level rises.

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

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

The law of Archimedes states that the buoyant force is equal to the weight of the fluid displaced by the body immersed in it. If the pushing force is less than the weight of the body, then it sinks; if it is equal to the weight of the body, it floats.

Experiment No. 1 (see Appendix 1)

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

Conclusion: From the side of the water, a force directed upwards acted on the plasticine ball. Therefore, the length of the gum 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 that the pushing force is greater.

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

In order for a body not to sink, 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 #2: (See Appendix 2)

She poured water into a glass and set it outside. When the water froze, the glass burst. I put the formed ice in a container of cold water and saw that it was floating.

In another container, salt the water well 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 somewhat greater than the density of frozen water, that is, ice. As the density of the liquid increases, the buoyancy force increases.

Scientific facts:

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

2 fact Mikhail Lomonosov:

Ice does not sink because it has a density of 920 kg \ m3. And water is denser -1000 kg \ m3.

Conclusion:

I found 2 reasons for the unsinkability of ice:

a buoyant force acts on any body immersed in water;

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, as any normal substance should be, is denser than liquid water. In winter, the denser ice that freezes from above would sink in 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, and beyond them the oceans. Our beautiful blooming green world would become

solid icy desert, in some places covered with a thin layer of melt water. One of these unique properties of water is its ability to expand when it freezes. After all, all substances during freezing, that is, during the transition from a liquid to a solid state, are compressed, and water, on the contrary, expands. Its volume increases by 9%. But when ice forms on the surface of the water, it, being between 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. Falling into small cracks that are always found in stones, rainwater expands when it freezes and destroys the stone. Thus, gradually, the stone surface becomes capable of sheltering plants that, with their roots, complete this process of destruction of stones and lead to the formation of soil on the slopes of the mountains.

Ice is always on the surface of the water and serves as a real heat insulator. That is, the water under it is not so cooled, the ice coat reliably protects it from frost. That is why a rare 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 to ice is an important property of water. This feature often has to be taken into account in practical life. If you leave a barrel of water in the cold, then the water, freezing, will break the barrel. For the same reason, you should not leave water in the radiator of a car in a cold garage. In severe frosts, you need to be wary of the slightest interruption in the supply of warm water through the water heating pipes: water that has stopped in the outer pipe can freeze quickly, 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.

Conclusion.

So after doing a lot of work, I figured it out. That my hypothesis about why ice does not sink was confirmed.

Causes of unsinkable ice:

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

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

If water were normal and not a unique liquid, we wouldn't enjoy skating. We don't roll on glass, do we? But it is much smoother and more attractive than ice. But glass is a material on which the skates will not slide. But on ice, even of not very good quality, skating is a pleasure. You will ask why? The fact is that the weight of our body presses on a very thin blade of the skate, which exerts strong pressure on the ice. As a result of this pressure from the ridge, the ice begins to melt with the formation of a thin film of water, over which the ridge glides excellently.

Bibliography

Children's encyclopedia "I know the world."

Zedlag W. "The Amazing on Planet Earth."

Internet resources.

Rakhmanov A. I. "Natural Phenomena".

Encyclopedia "World of Nature".

Attachment 1