Research work "Why doesn't ice sink?" Why doesn't ice sink in water? — Other It’s easy to make sure that ice floats in water

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. The essence of this mysterious phenomenon and I'm going to reveal it.

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 is also positive points. 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

One more 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 body volume, greatly facilitating its transition to solid state. But when water freezes, it does not decrease in volume, but, on the contrary, increases. And therefore the pressure, preventing water expansion, lowers its freezing point.

That's all I can say about it interesting phenomenon. I hope you learned something new. Good luck on your travels!

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. After all, the water at the top of the lake is winter conditions, freezes and turns 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 occupy more space than 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.

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 into this liquid solid, he will drown immediately. The same will happen with lead, and with tin, and with many other substances. It turns out, as a rule, solids always drown in the liquids that form 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 very coldy you need to be wary of the slightest interruption in supply warm water through water heating pipes: 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 you open the cylinder, then at this temperature and atmospheric pressure the water will instantly turn to 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 more high temperature, and there is nothing surprising here if we 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 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.

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"in 3rd grade. “Why doesn’t ice sink in water?” the teacher asks the children. And kids, without deep knowledge of physics, begin to reason. “Perhaps this is magic?” - says one of the children.

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

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

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

Density of ice and water

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

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

Properties of water

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

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

What changes happen to water when it freezes?

The reason why ice does not sink in water is due to hydrogen bonds, which change when water freezes. As you know, water consists of one oxygen atom and two hydrogen atoms. They are attached 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 glass bottle water - frozen water can create large cracks even in concrete. if you have liter bottle ice and a liter bottle of water, then an 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 the lake while swimming upper layer The water is always pleasant and warm, but when you lower your feet deeper, you feel the cold of the lower layer.

The importance of the 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 occurs and what it means for the planet. Thus, the buoyancy of ice has important consequences for life on Earth. in winter in cold places - this allows fish and other aquatic animals to survive under the ice blanket. 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.

One of the most common substances on Earth: water. It, like air, is necessary for us, but sometimes we don’t notice it at all. She just is. But it turns out that ordinary water can change its volume and weigh either more or less. When it is heated and cooled, truly amazing things happen, which we will learn about today.

Muriel Mandell, in her entertaining book “Phycisc Experiments for Children,” outlines interesting thoughts about the properties of water, on the basis of which not only young physicists can learn a lot of new things, but also adults will refresh their knowledge, which has not had to be used for a long time, so it turned out to be slightly forgotten.

Today we will talk about the volume and weight of water. It turns out that the same volume of water does not always weigh the same. And if you pour water into a glass and it does not spill over the edge, this does not mean that it will fit in it under any circumstances.

1. When heated, water increases in volume

Place the jar filled with water in a saucepan filled with about five centimeters of boiling water and maintain a simmer over low heat. The water from the jar will begin to overflow. This happens because when water heats up, like other liquids, it begins to take up more space. repulse each other with greater intensity and this leads to an increase in the volume of water.

2. When water cools, it contracts

Let the water in the jar cool at room temperature, or pour new water, and put it in the refrigerator. After a while, you will discover that the previously full jar is no longer full. When cooled to 3.89 degrees Celsius, water decreases in volume as the temperature decreases. The reason for this was a decrease in the speed of movement of molecules and their approach to each other under the influence of cooling.

It would seem that everything is very simple: what colder water, the less volume it takes up, but...

3. ...the volume of water increases again when it freezes

Fill the jar with water to the brim and cover with a piece of cardboard. Place it in the freezer and wait until it freezes. You will find that the cardboard “lid” has been pushed out. At temperatures between 3.89 and 0 degrees Celsius, that is, when approaching its freezing point, water begins to expand again. She is one of the few known substances, having a similar property.

If you use a tight lid, the ice will simply smash the jar. Have you ever heard that even water pipes can be broken by ice?

4. Ice is lighter than water

Place a couple of ice cubes in a glass of water. Ice will float on the surface. When water freezes, it increases in volume. And, as a result, ice is lighter than water: its volume is about 91% of the corresponding volume of water.

This property of water exists in nature for a reason. It has a very specific purpose. They say that in winter the rivers freeze. But in reality this is not entirely true. Usually only a small top layer freezes. This ice sheet does not sink because it is lighter than liquid water. It slows down the freezing of water at the depth of the river and serves as a kind of blanket, protecting fish and other river and lake life from severe winter frosts. Studying physics, you begin to understand that a lot of things in nature are arranged expediently.

5. Tap water contains minerals

Pour 5 tablespoons of regular tap water into a small glass bowl. When the water evaporates, a white border will remain on the bowl. This rim is formed by minerals that were dissolved in the water as it passed through the layers of soil.

Look inside your kettle and you will see mineral deposits. The same coating forms on the drainage hole in the bathtub.

Try evaporating rainwater to test for yourself whether it contains minerals.

If you combine water with other liquids, you may find that water does not mix with some. Thanks to these properties of substances, you can make the most beautiful.