Kim Irina, 4th grade student
Research paper on the topic “Why doesn’t ice sink?”
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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
Polar ice blocks and icebergs drift in the ocean, 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 around us” 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 sets up rapid weathering cycles and certain chemicals released on the surface can dissolve minerals. In general, the freezing of water involves processes and possibilities that the physical properties of other liquids do not suggest.
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. Thus, hot water or ice is 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 by covalent bonds that 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 break and form bonds as easily as at high temperatures. 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 up 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 ice water bottle will be lighter. 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 a lake, while swimming, the top layer of water is always pleasant and warm, but when you put 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.
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 -39ºC, it is not suitable for thermometers used in harsh temperature environments.
Water also expands when heated and contracts when cooled. However, in the cooling range from approximately +4 ºC to 0 ºC it expands. This is why water pipes can burst in winter if the water in them has frozen and large masses of ice have formed. The ice pressure on the pipe walls is enough to cause them to burst.
Water expansion
Since water expands when cooled, the density of ice (i.e. its solid form) is less than that of liquid water. In other words, a given volume of ice weighs less than the same volume of water. This 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 increasing volume (as water cools), 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 above water of 2 cm, 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 water in its solid state 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 approximately 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 created by the upper layers of water. A layer of water one kilometer thick presses with a force of about 100 atmospheres.
Comparison of the densities of water and ice
Can the density of water be less than the density of ice and does this mean that he will drown in it? The answer to this question is affirmative, which is easy to prove with 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 of water at a temperature of +20 ºС. What are we observing? The ice quickly sinks and sinks, gradually beginning to melt. This happens 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 hydrogen isotopes 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.
Meaning 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 cold weather occurs, first at temperatures above +4 ºС, colder water from the surface of the reservoir sinks down, and warm (lighter) water rises. This process is called vertical circulation (mixing) of water. When it reaches +4 ºС throughout the entire reservoir, this process stops, since from the surface the water already at +3 ºС becomes lighter than that which is below. Water expands (its volume increases by approximately 10%) and its density decreases. As a consequence of the fact that the colder layer is on top, water freezes on the surface and an ice cover appears. Due to its crystalline structure, ice has poor thermal conductivity, meaning it retains heat. The ice layer acts as a kind of heat insulator. And the water under the ice retains its heat. Thanks to the thermal insulating properties of ice, the transfer of “cold” to the lower layers of water is sharply reduced. Therefore, at least a thin layer of water almost always remains at the bottom of a reservoir, which is extremely important for the life of its inhabitants.
Thus, +4 ºС - the temperature of maximum density of water - is the temperature of survival of living organisms in a reservoir.
Use in everyday life
Mentioned above was the possibility of water pipes bursting when water freezes. To avoid damage to the water supply system at low temperatures, there should be no interruptions in the supply of warm water that flows through the heating pipes. A 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 children and adults. Have you ever wondered why ice is so slippery? For example, glass is also slippery, and also smoother and more attractive than ice. But skates don't glide on it. Only ice has such a specific delightful 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, against which the steel blade of the skate slides.
Difference in freezing of wax and water
Experiments show that the surface of an ice cube forms a certain bulge. This is due to the fact that freezing in the middle occurs last. And expanding during the transition to a solid state, this bulge rises even more. This can be counteracted by the hardening of wax, which, on the contrary, forms a depression. This is explained by the fact that the wax contracts after turning into a solid state. Liquids that contract uniformly when frozen form a somewhat concave surface.
To freeze water, it is not enough to cool it to the freezing point of 0 ºC; this temperature must be maintained through 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 the transformation from its surroundings, 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 consists of hydrogen and oxygen. When other substances (soluble and insoluble in water) get into the water, it becomes polluted, which is why 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 a “universal solvent.”
Guarantor of stable air temperature
Water heats up slowly due to its high heat capacity, but, nevertheless, the cooling process occurs much more slowly. This makes it possible for the oceans and seas to accumulate heat in the summer. The release of heat occurs in winter, due to which there is no sharp change in air temperature on the territory of our planet throughout the year. Oceans and seas are the original and natural heat accumulator on 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 density of water is 1000 kg/m³, of ice - 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 very rare in nature, an exception to the general rule. Only metal and cast iron (an alloy of the metal iron and the nonmetal carbon) have similar properties.
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 the warm water below.
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 in water? Why is water able to dissolve so many different substances? Why is a towel able to absorb water from bottom to top, contrary to the laws of gravity? If we assume that water came to us from another world, these and other mysteries surrounding water will seem less difficult to understand.
If water behaved like all other substances on earth, you and I would not exist.
Water is something so simple that we rarely think about it. However, there is nothing more mysterious than plain water. The biggest mystery of water: why ice floats. Any other substance, passing from a liquid to a solid state, becomes heavier as the density of the substance increases.
Water, passing from a liquid to a solid state, on the contrary, becomes lighter.
In the structure of ice, water particles are arranged in a very orderly manner, with a lot of free space between the particles. The volume of ice is greater than the volume of water from which it was formed. The volume is larger, the density is lower - ice is lighter than water, so it does not sink in water. Huge blocks of ice and icebergs do not sink in water.
- When the ice turns back into water, the particles become hundreds of thousands of times more active, and the free space is filled.
The liquid form of water is denser and heavier than the solid form. Water becomes heaviest at a temperature of + 4°C. As the temperature rises, water particles become more active, which leads to a decrease in its density.
No matter how cold the winter is over the reservoir, the water temperature at the bottom is constant: +4°C. Anything that lives on the bottom can survive long winters under the ice. Ice is lighter than water. With its shell on the surface of the water, it protects the bottom of the reservoir from freezing.
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