Each of us watched ice plates floating on the river in the spring. But why are they don't drown? What keeps them on the surface of the water?
It seems that despite their weight, something simply does not allow them to fall down. I am going to reveal the essence of this mysterious phenomenon.
Why doesn't ice sink?
The thing is that water is very unusual substance. It has amazing properties that we sometimes simply don’t notice.
As you know, almost all things in the world expand when heated and contract when cooled. This rule also applies to water, but with one interesting note: when cooled from +4°C to 0°C, water begins to expand. This explains the low density of ice masses. Expanded from the phenomenon above, the water becomes lighter than the one in which it is located, and begins to drift on its surface.
How dangerous is this ice?
The phenomenon described above is often found in nature and everyday life. But if you start to forget about it, it can become the source of many problems. For example:
- in winter, frozen water can burst water pipes;
- the same water, freezing in mountain cracks, contributes to rock destruction, causing mountain falls;
- we must not forget drain water from car radiator to avoid the above situations.
But there are also positive aspects. After all, if water did not have such amazing properties, then there would not be such a sport as skating. Under the weight of a person’s body, the blade of the skate puts so much pressure on the ice that it simply melts, creating a film of water ideal for gliding.
Water in the ocean depths
Another interesting point is that even despite the zero temperature in the ocean (or sea) depths, the water there doesn't freeze, does not become an ice block. Why is this happening? It's all about pressure, which is exerted by the upper water layers.
In general, pressure helps solidify various liquids. It causes a reduction in the volume of the body, significantly facilitating its transition to a solid state. But when water freezes, it does not decrease in volume, but on the contrary, it increases. And therefore the pressure, preventing water expansion, lowers its freezing point.
That's all I can tell you about this interesting phenomenon. I hope you learned something new. Good luck on your travels!
Municipal educational autonomous institution
secondary school with. Vasylivki
Research
Why doesn't ice sink in water?
Students of grade 3 "b"
Belogubova Sophia
Head: 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. Archimedes' Law……………………………………………………….
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 not? Understanding the laws of buoyancy allows engineers to build ships from metals that float and do not sink.
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.
Set a goal:
Determine the reasons for the unsinkability of ice.
I identified a number of tasks:
Find out the floating conditions of bodies;
Find out why ice doesn't sink;
Conduct an experiment to study buoyancy.
She put forward a hypothesis:
Perhaps ice does not sink because water is denser than ice.
Research methods:
Theoretical analysis of literature;
Observation method;
Practical method.
Practical material will be useful to me in reading lessons and the surrounding world.
Main part
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 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 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. I marked the new water level with a felt-tip pen.
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: (see Appendix 2)
She poured water into a glass and put it outside. When the water froze, the glass burst. I put the formed ice in a container with cold water and saw that it was floating.
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 a liquid increases, the buoyant 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:
any body immersed in water is subject to a buoyant force;
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 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 frozen. 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 often has to 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 severe frosts, you need to be wary of the slightest interruption in the supply of warm water through water heating pipes: the 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.
Conclusion.
So, after doing a lot of work, I understood. That my hypothesis about why ice doesn’t sink was confirmed.
Reasons for the unsinkability of 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, even if it’s not of very 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.
Bibliography
Children's encyclopedia "I explore the world."
Zedlag U. “Amazing things on planet Earth.”
Internet resources.
Rakhmanov A. I. “Phenomena of Nature.”
Encyclopedia "Natural World".
Annex 1
Appendix 2
Appendix 3
Kim Irina, 4th grade student
Research paper on the topic “Why doesn’t ice sink?”
Download:
Preview:
Municipal State 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 sinking) allows engineers to build ships from metals that are heavier than water, and to design airships and balloons that can float 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 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 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. I marked the new water level with a felt-tip pen.
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 (not full), 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 sink in clean water, and spoiled eggs float, 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. I put the formed ice in a container with cold water and saw that it was floating.
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:
- Any body immersed in water is subject to a buoyant force.
- 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 icy 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 frozen. 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 often has to 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 severe frosts, you need to be wary of the slightest interruption in the supply of warm water through water heating pipes: the 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. The submarine is 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, even if it’s not of very 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
Young children very often ask interesting questions to adults, and they cannot always answer them right away. In order not to seem stupid to your child, we recommend that you familiarize yourself with a complete and detailed, well-founded answer regarding the buoyancy of ice. After all, it floats, not drowns. Why is this happening?
How to explain complex physical processes to a child?
The first thing that comes to mind is density. Yes, in fact, ice floats because it is less dense than . But how to explain to a child what density is? No one is obligated to tell him the school curriculum, but it’s quite possible to boil it all down to what it is. After all, in fact, the same volume of water and ice has different weights. If we study the problem in more detail, we can voice several other reasons besides density.
not only because its reduced density prevents it from sinking lower. The reason is also that small air bubbles are frozen in the ice. They also reduce the density, and therefore, in general, it turns out that the weight of the ice plate becomes even less. When ice expands, it does not take in more air, but all those bubbles that are already inside this layer remain there until the ice begins to melt or sublimate.
Conducting an experiment on the force of expansion of water
But how can you prove that ice is actually expanding? After all, water can also expand, so how can this be proven under artificial conditions? You can conduct an interesting and very simple experiment. To do this you will need a plastic or cardboard cup and water. The quantity does not have to be large; you do not need to fill the glass to the brim. Also, ideally you need a temperature of about -8 degrees or lower. If the temperature is too high, the experience will last unreasonably long.
So, water is poured inside, we need to wait for ice to form. Since we have chosen the optimal temperature at which a small volume of liquid will turn into ice within two to three hours, you can safely go home and wait. You need to wait until all the water turns into ice. After some time we look at the result. A cup that is deformed or torn by ice is guaranteed. At a lower temperature, the effects look more impressive, and the experiment itself takes less time.
Negative consequences
It turns out that a simple experiment confirms that ice blocks really expand when the temperature decreases, and the volume of water easily increases when freezing. As a rule, this feature causes a lot of problems for forgetful people: a bottle of champagne left on the balcony for a long time on New Year’s Eve breaks due to exposure to ice. Since the expansion force is very large, it cannot be influenced in any way. Well, as for the buoyancy of ice blocks, there is nothing to prove here. The most curious can easily carry out a similar experiment in spring or autumn on their own, trying to drown pieces of ice in a large puddle.
We are not at all surprised by floating ice blocks at the beginning of spring, when reservoirs begin to free themselves from winter “clothing” and reveal the beauty of fresh water to the human eye. We are so accustomed to this natural phenomenon that we don’t even think about it and wonder why the ice doesn’t melt? And if you think about it, you don’t immediately remember examples where solids like ice float in liquids that are formed when they melt. You can melt paraffin or wax in a container and throw a piece of the same substance, only in a solid state, into the resulting puddle. And what do we see? Wax and paraffin safely sink in the liquid that is formed as a result of their melting.
Why doesn't ice sink in water? The fact is that water in this example is a very rare and inherently unique exception. In nature, only metal and cast iron behave similarly to a piece of ice floating on the surface of water.
If the ice were heavier than water, it would certainly sink under its own weight and at the same time displace the water located in the lower part of the reservoir to the surface. As a result, the entire reservoir would freeze to the very bottom! However, when water freezes, a completely different situation occurs. The transformation of water into ice increases its volume by approximately 10% and it is at this moment ice has less density than water itself. It is for this reason that ice floats on the surface of the water and does not sink. The same thing can be observed when a paper boat, the density of which is much times less than the density of water, is lowered onto the water. If the boat had been made of wood or other material, it would certainly have sunk. If we compare density indicators in numbers, then, for example, if the density of water is one, then the density of ice will be equal to 0.91.
The increase in the volume of water when it turns into ice should be taken into account in everyday life. It is enough to leave a barrel filled to the top with water in the cold, and the liquid will freeze and burst the container. That is why it is not recommended to leave water in the radiator of a vehicle that is parked in the cold. Also, in severe frosts, you must be wary of interruptions in the supply of warm water running through the heating pipes. If there is water left in the outer pipe, it will instantly freeze, which will inevitably lead to damage to the water supply.
As is known, in oceans and seas at great depths, where the temperature is below zero, water still does not freeze and does not turn into block of ice. It is quite simple to explain - the upper layers of water create enormous pressure. For example, a one kilometer layer of water presses with a force of more than one hundred atmospheres.
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, even if it’s not of very 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 puts strong pressure on 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.
How to explain complex physical processes to a child?
The first thing that comes to mind is density. Yes, in fact, ice floats because it is less dense than water. But how to explain to a child what density is? No one is obligated to tell him the school curriculum, but it’s quite possible to boil it down to the fact that ice is easier. After all, in fact, the same volume of water and ice has different weights. If we study the problem in more detail, we can voice several other reasons besides density.
Ice does not sink in water not only because its reduced density prevents it from sinking lower. The reason is also that small air bubbles are frozen in the ice. They also reduce the density, and therefore, in general, it turns out that the weight of the ice plate becomes even less. When ice expands, it does not take in more air, but all those bubbles that are already inside this layer remain there until the ice begins to melt or sublimate.
Conducting an experiment on the force of expansion of water
But how can you prove that ice is actually expanding? After all, water can also expand, so how can this be proven under artificial conditions? You can conduct an interesting and very simple experiment. To do this you will need a plastic or cardboard cup and water. The quantity does not have to be large; you do not need to fill the glass to the brim. Also, ideally you need a temperature of about -8 degrees or lower. If the temperature is too high, the experience will last unreasonably long.
So, water is poured inside, we need to wait for ice to form. Since we have chosen the optimal temperature at which a small volume of liquid will turn into ice within two to three hours, you can safely go home and wait. You need to wait until all the water turns into ice. After some time we look at the result. A cup that is deformed or torn by ice is guaranteed. At a lower temperature, the effects look more impressive, and the experiment itself takes less time.
Negative consequences
It turns out that a simple experiment confirms that ice blocks really expand when the temperature decreases, and the volume of water easily increases when freezing. As a rule, this feature causes a lot of problems for forgetful people: a bottle of champagne left on the balcony for a long time on New Year’s Eve breaks due to exposure to ice. Since the expansion force is very large, it cannot be influenced in any way. Well, as for the buoyancy of ice blocks, there is nothing to prove here. The most curious can easily carry out a similar experiment in spring or autumn on their own, trying to drown pieces of ice in a large puddle.
No one doubts that ice floats on water; everyone has seen this hundreds of times both on the pond and on the river.
But how many people have thought about this question: do all solids behave the same way as ice, that is, float in the liquids formed when they melt?
Melt paraffin or wax in a jar and throw another piece of the same solid substance into this liquid, it will immediately sink. The same will happen with lead, and with tin, and with many other substances. It turns out that, as a rule, solids always sink in liquids that are formed when they melt.
Handling water most often, we are so accustomed to the opposite phenomenon that we often forget this property, characteristic of all other substances. It must be remembered that water is a rare exception in this regard. Only the metal bismuth and cast iron behave in the same way as water.
If ice were heavier than water and did not stay on its surface, but sank, then even in deep reservoirs the water would freeze completely in winter. In fact, ice falling to the bottom of the pond would displace the lower layers of water upward, and this would happen until all the water turned into ice.
However, when water freezes, the opposite occurs. The moment water turns to ice, its volume suddenly increases by about 10 percent, making ice less dense than water. That is why it floats in water, just as any body floats in a liquid of high density: an iron nail in mercury, a cork in oil, etc. If we assume the density of water to be equal to unity, then the density of ice will be only 0.91. This figure allows us to find out the thickness of the ice floe floating on the water. If the height of the ice floe above the water is, for example, 2 centimeters, then we can conclude that the underwater layer of the ice floe is 9 times thicker, that is, equal to 18 centimeters, and the entire ice floe is 20 centimeters thick.
In the seas and oceans there are sometimes huge ice mountains - icebergs (Fig. 4). 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.
The sudden increase in volume during the transition of liquid water into ice is an important feature of water. This feature often has to 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 severe frosts, you need to be wary of the slightest interruption in the supply of warm water through water heating pipes: the water that has stopped in the outer pipe can quickly freeze, and then the pipe will burst.
Freezing in rock cracks, water often causes mountain collapses.
Let us now consider one experiment that is directly related to the expansion of water when heated. Staging this experiment requires special equipment, and it is unlikely that any reader can reproduce it at home. Yes, this is not a necessity; The experience is easy to imagine, and we will try to confirm its results using examples that are familiar to everyone.
Let’s take a very strong metal, preferably a steel cylinder (Fig. 5), pour some shot into the bottom, fill it with water, secure the lid with bolts and begin turning the screw. Since water compresses very little, you won’t have to turn the screw for a long time. After just a few revolutions, the pressure inside the cylinder rises to hundreds of atmospheres. If you now cool the cylinder even 2-3 degrees below zero, the water in it will not freeze. But how can you be sure of this? If we open the cylinder, then at this temperature and atmospheric pressure the water will instantly turn into ice, and we will not know whether it was liquid or solid when it was under pressure. The sprinkled pellets will help us here. When the cylinder has cooled, turn it upside down. If the water is frozen, the shot will lie at the bottom; if it is not frozen, the shot will collect at the lid. Let's unscrew the screw. The pressure will drop and the water will definitely freeze. After removing the lid, we make sure that all the shot has collected near the lid. This means that water under pressure did not freeze at temperatures below zero.
Experience shows that the freezing point of water decreases with increasing pressure by approximately one degree for every 130 atmospheres.
If we began to base our reasoning on the basis of observations of many other substances, we would have to come to the opposite conclusion. Pressure usually helps liquids solidify: under pressure, liquids freeze at a higher temperature, and this is not surprising if you remember that most substances decrease in volume when they solidify. Pressure causes a decrease in volume and this facilitates the transition of liquid to solid state. When water hardens, as we already know, it does not decrease in volume, but, on the contrary, expands. Therefore, pressure, preventing the expansion of water, lowers its freezing point.
It is known that in the oceans at great depths the water temperature is below zero degrees, and yet the water at these depths does not freeze. This is explained by the pressure created by the upper layers of water. A layer of water one kilometer thick presses with a force of about one hundred atmospheres.
If water were a normal liquid, we would hardly experience the pleasure of skating on ice. It would be the same as rolling on perfectly smooth glass. Skates do not slip on glass. It's a completely different matter on ice. Skating on ice is very easy. Why? Under the weight of our body, the thin blade of the skate produces quite strong pressure on the ice, and the ice under the skate melts; a thin film of water is formed, which serves as an excellent lubricant.
