Cold air rises or. How does heat travel in liquids? Convection in a gaseous medium

AIR .

WHERE WARMER.

Target. Reveal that warm air is lighter than cold air and rises.

game material. Two thermometers, kettle with hot water.

Game progress. Children find out if the room is cool, then where it is warmer - on the floor or on the sofa, that is, higher or lower, and compare their assumptions with the readings of thermometers. Children perform actions: hold their hand above or below the battery; without touching the kettle, hold your hand above the water. They find out with the help of actions where the air is warmer: from above or from below (everything that is lighter rises up, which means warm air is lighter than cold and warmer from above).

WIND IN THE ROOM ("LIVE SNAKE")

Target. Reveal how wind is formed, that wind is a stream of air, that hot air rises, and cold air descends.

game material. Two candles, "snake" (a circle cut in a spiral and suspended from a thread).

Game progress. An adult lights a candle and blows on it. Children find out why the flame is deflected (air flow is affected). An adult offers to consider the “snake” of its spiral design and shows the children the rotation of the “snake” above the candle (the air above the candle is warmer, the “snake” rotates above it, but does not go down, because warm air raises it). Children find out that the air makes the “snake” rotate, and with the help of heating devices, they perform the experiment on their own

An adult invites children to determine the direction of wind movement from above and below the doorway. Children explain why the direction of the wind is different (warm air in the apartment rises and exits through the slot at the top, and cold air is heavier, and it enters the room from below; after a while, the cold air will heat up in the room, rise up and go outside through the slot at the top, and cold air will come in its place again and again). This is how wind occurs in nature. Draw the results of the experiment.

SUBMARINE.

Target. Find that air is lighter than water; reveal how air displaces water, how air leaves water.

game material. curved tube for a cocktail plastic glasses, a container of water.

Game progress. Children find out what will happen to the glass if it is lowered into water, whether it can rise from the bottom itself. They perform actions: they immerse a glass in water, turn it upside down, bring a curved tube under it, blow air under it. At the end of the experiment, conclusions are drawn: the glass is gradually filled with water, air bubbles come out of it; air is lighter than water - entering the glass through a tube, it displaces water from under the glass and rises, pushing the glass out of the water.

STUNNING AIR (1)

Target. Find out that air, when compressed, takes up less space; compressed air has the power to move objects.

game material. Syringes, a container of water (tinted).

Game progress. Children examine the syringe, it

device (cylinder, piston) and demonstrate actions with it: press the piston up, down without water; they try to squeeze the piston when the hole is closed with a finger; draw water into the piston when it is at the top and bottom. An adult invites children to explain the results of the experience, to talk about their feelings when performing actions. At the end of the experiment, the children find out that air, when compressed, takes up less space; compressed air has the power to move objects.

STUNNING AIR (2)

Target. Find that compressed air takes up less space. Compressed air has the power to move objects.

game material. Pipettes, a container of water (tinted).

Game progress. Children examine the pipette device (rubber cap, glass cylinder). They conduct the experiment similarly to the previous one (squeeze and unclench the cap).

DRY OUT OF WATER

(Option 1 - Napkin in a glass)

Target.

game material. A container with water, a glass with a napkin attached to the bottom.

Game progress. The adult invites the children to explain what it means to “get out of the water dry”, whether this is possible, and to find out if it is possible to lower the glass into the water and not wet the napkin lying at the bottom. Children make sure that the napkin at the bottom of the glass is dry. Then they turn the glass upside down, carefully immerse it in water, without tilting the glass to the very bottom of the container, actually lift it out of the water, let the water drain without turning the glass over. The adult offers to determine if the napkin got wet (not wet), explain what prevented the water from getting wet (air in the glass) and what will happen to the napkin if the glass is tilted (air bubbles will come out, and water will take its place, the napkin will get wet). Children repeat the experience on their own.

DRY OUT OF WATER.

(Option 2 - Flag on the bar)

Target. Determine what air takes up space.

game material. water container, wooden bars with flags, cans (a bar with a flag should freely enter them).

Game progress. An adult invites children to lower the bar into the water, watch how it swims. They find out why it does not sink (a tree is lighter than water), how it can be drowned (lowered to the bottom), not wetted (lowered into water, covered with a jar). Children do things on their own. Discuss why the bar is not wet (because there is air in the jar).

WHAT IS FASTER?

Target.

game material. Two sheets of writing paper.

Game progress. An adult suggests thinking, if you simultaneously release two sheets from your hands: one horizontally, the other vertically (shows how to hold it in your hands), then which one will fall faster. Listens to answers, offers to check. Demonstrates experience. Why does the first leaf fall slowly, what delays it (air presses on it from below). Why does the second sheet fall faster (it falls edgewise, and therefore there is less air under it). The children conclude: there is air around us, and it presses on all objects (this is atmospheric pressure).

FOCUS "WHY DOES IT NOT HAPPEN?"

Target. Detect atmospheric pressure.

game material. Glasses of water, postcards.

Game progress. The adult invites the children to turn the glass over without spilling water from it. Children make assumptions, try. Then the adult fills the glass with water to the brim, covers it with a postcard and, holding it lightly with his fingers, turns the glass upside down. He removes his hand - the card does not fall, the water does not pour out (unless the paper is perfectly horizontal and pressed to the edges). Why does water not pour out of a glass when there is a sheet of paper under it (air presses on a sheet of paper, it presses the sheet to the edges of the glass and prevents water from pouring out, that is, the reason is air pressure).

HOMEMADE THERMOMETER

Target. Demonstrate how air expands when heated and pushes water out of a vessel.

game material. Glass tube or rod (transparent) from a ballpoint pen, a bottle of 50-100 ml, a little tinted water.

Game progress. Children consider the "thermometer": how it works, its device (bottle, tube and cork); with the help of an adult, a model of a thermometer is made. Make a hole in the cork with an awl, insert it into the bottle. Then they take a drop of tinted water into the tube and stick the tube in so that the drop of water does not jump out. The bottle heats up in the hands, a drop of water rises.

PIVOT

Target. Reveal that air has elasticity. Understand how air power (movement) can be used

game material. Pinwheel, material for making for each child: paper, scissors, sticks, carnations.

Game progress. An adult shows the children a turntable in action. Then he discusses with them why it is spinning (the wind hits the blades that are turned at an angle to it, and this causes the turntable to move). An adult invites children to make a turntable according to the algorithm, consider and discuss the features of its design. Then he organizes games with a turntable in the street; children observe under what conditions it spins faster.

REACTIVE BALL.

Target.

game material. Balloons.

Game progress. Children with the help of an adult inflate a balloon, lower it and pay attention to the trajectory and duration of its flight. They find out that in order for the ball to fly longer, it is necessary to inflate it more: the air, escaping from the "neck", makes the ball move in the opposite direction. An adult tells the children that the same principle is used in jet engines.

STRAW GILM.

Target. Reveal that air has elasticity. Understand how air power (movement) can be used.

game material. Raw potatoes, two straws for a cocktail (for each child).

Game progress. Children take a straw upper part without closing the top hole with your finger; then, from a height of 10 cm, they stick it into a potato with a sharp movement; they observe what happened to the straw (it bent, did not stick in), take the second straw by the top, this time closing the upper hole with a finger; they also stick sharply into the potato and observe what happened to the straw (it stuck). Children find out that inside the second straw there is air that presses on the walls and does not allow it to bend. Children conclude: in the first case, the air freely escaped from the straw and it bent; in the second case, the air could not escape from the straw, since the hole was closed. In addition, when potatoes hit the straw, the pressure increased even more, strengthening the walls of the straw.

PARACHUTE.

Target. Reveal that air has elasticity. Understand how air power (movement) can be used.

game material. Parachute, toy people, a container of sand.

CANDLE IN A JAR.

Target. Reveal that the composition of the air changes during combustion (there is less oxygen), that oxygen is needed for combustion. Learn how to extinguish a fire.

game material. Candle, jar, bottle with cut bottom.

HOW TO BLOW OUT A CANDLE FROM A FUNNEL.

Target. Reveal the features of the air vortex.

game material. Candle, funnel.

STRONG MATCHBOX.

Target. Determine the elasticity of air.

game material. Match boxes.

LARGE - SMALL.

Target. Reveal that air contracts when cooled, and expands when heated (takes up more space).

game material. Plastic bottles with corks, balloon, coin.

FOCUS "DRY OUT OF WATER"

Target. Demonstrate Existence atmospheric pressure, the fact that the air during cooling occupies a smaller volume (compresses).

game material. A plate with water covering the bottom, a coin, a glass.

WHY QUESTIONS.

Target. Analyze and draw conclusions based on knowledge of the properties of air: warm air rises, i.e., it is lighter than cold air; air is a poor conductor of heat.

game material. Tissue paper, stand with a needle.

Game progress. An adult suggests making pinwheels from thin tissue paper: cut out a rectangle, fold it along the middle lines and straighten it again (the center of gravity is found), put the piece of paper on the tip of the protruding needle so that the needle props it up exactly at that point. Carefully bring the hand closer - the rotation of the piece of paper begins, move it away - the rotation stops. They conclude: the air rises from the bottom up, pressing on the piece of paper and causing it to rotate, since the piece of paper has a slope at the folds.

This article aims to give an idea in simple terms of how air is exchanged in a room, and how to influence it in order to obtain optimal air parameters. Therefore, the article allows for simplifications and ignoring some physical parameters. If you want exact scientific formulations, then enter the necessary term into the search and you will find a lot of descriptions and data.

Part 1 - Science

To make different formulas and numbers more understandable, we will often consider them with examples. And for such examples, we will use the following values:

The average room is 5 by 6 meters with ceilings of 2.5 meters.

The optimal air parameters are 18C and 60% humidity.

Speaking of air in general, there is often a 1 meter cube of air.

A bit of theory

There is a certain amount of water (steam) in the air, and this amount is measured by the concept of humidity. Humidity is indicated both relatively (for example, 50-70%) and absolutely (for example, 10 grams / cubic meter). Of course, we are used to the first option, but before talking about relative humidity must be said about absolute humidity, and its relation to air temperature.

Absolute humidity

Absolute air humidity is the amount of water (steam) (grams) in the air (1 meter cube). And the exact amount of water in the air is called absolute humidity.

Maximum absolute humidity

It is clear that air cannot contain an infinite amount of water, there is a maximum of water that air can contain, that is, 100% humidity. And this amount of water is called - the maximum absolute humidity.

And the air, depending on the temperature, can contain a certain amount of water (steam), and the higher the air temperature, the more water can be evaporated in the air, and the lower the air temperature, the less water can be evaporated. And at sub-zero temperatures, water practically does not evaporate into the air. Therefore than colder air(below 5C) the drier it is and no matter what the relative humidity is.

Here is a graph of the maximum absolute humidity at different temperatures:

As you can see, the higher the temperature, the more water can evaporate in it.

Relative Humidity

The ratio of absolute humidity and the maximum possible absolute humidity at a particular temperature is called Relative Humidity. That is, if at 18C the maximum absolute humidity (per m3 of air) is 15.4 grams (seen from the graph above), then for 60% relative humidity there should be 9.2 grams of water (per m3 of air). Because 9.2/15.4 is 60%.

Now knowing this, we can explain why the relative humidity drops when the air is heated. With heating, the moisture capacity (maximum absolute humidity) of the air increases, but the amount of water in it (absolute humidity) remains the same, so the ratio of water to the maximum decreases. For example, if you have air in the room at 0C and humidity 100% (4.8 grams per m3 of air), then if you heat it up to 18C, then your relative humidity will be 31% (4.8 / 15.4)

Also, knowing the exact grams of water in the air gives us an idea of ​​how much water needs to be evaporated in it in order to achieve optimal humidity.

For example, let's take an average room and an optimal temperature. As we said earlier, at an air temperature of 18C and a humidity of 60%, this is 9.2 grams of water per cubic meter. And if your room is about 5x6m with 2.5m ceilings and if you have optimum temperature(18C) and humidity (60%), then you have approximately (multiply 5 x 6 x 2.5 x 9.2) 690 grams of water (steam) in your room in the air. And if you have a humidity of 20% at 18C in the same room, then you have about 230 grams of water in the air, and in order to achieve the optimal one, you need to evaporate (690-230) 460 grams of water in the air. Good household humidifiers release about 350 grams of water per hour. This means that you will need about an hour and a half of hydration to make the humidity optimal. (But we are getting ahead of ourselves, we will come to practice later.)

* If mathematics is not "close to you in spirit", then do not be discouraged, all these numbers do not need to be memorized at all, the main thing is to have a general idea of ​​\u200b\u200bwhat is at stake.

Once again, we repeat everything that needs to be learned from the theory:

• absolute humidity is the exact amount of water (steam) in the air
• maximum absolute humidity is the maximum possible amount of water in the air relative to a certain air temperature
• relative humidity is the ratio of absolute humidity to maximum absolute humidity.
• The higher the air temperature, the more water it can evaporate.
• the lower the air temperature, the less water can evaporate in it
• when heated, the amount of water in the air does not change, but the moisture content of the air changes

Seasons or the air outside the window

Of course, depending on the season, we have different air outside the window.

In summer, the air is hot and humid (in the heat, even at 20% relative humidity, there is a lot of water in the air), in Winter, it is cold and dry (as we said earlier, in cold weather, water practically does not evaporate in the air, so it is always dry in cold weather), in spring and autumn is cool and humid.

But in relation to our room and optimal conditions, the air outside the window can be divided not by the seasons, but by the difference in temperature and humidity. That is, warmer, or colder, or drier. And most often we are concerned about 2 conditions, these are:

• when the air outside the window is warmer / hotter (mostly summer), then abbreviated - Summer
• when the air outside is cold and dry (mostly winter), then abbreviated as Winter

And in the practical part of the article, we will write about these two states.

About the room

Which air descends and which rises?

It is widely known that warm air is lighter than cold air, so the temperature on the ceiling is higher than on the floor. But wet air lighter than dry, so the humidity on the ceiling is higher than on the floor. As a result, the air on the floor is colder and drier than on the ceiling, where it is warmer and more humid.

And what is the difference in humidity and temperature from ceiling to floor?

It depends on many parameters, ceiling height, room size, location of the heat generator (heater), moisture generator (humidifier), heat transfer, moisture transfer, air flow directions (ventilation, ventilation), etc. But in general, 2-4 degrees and 5-10% humidity are noted. But with an intensive exchange of air, heat, humidity (for example, a window is open, heating, fan, humidifier / evaporative cooler is on), and high ceilings, the difference can reach 5-10 degrees, and 10-30% humidity.

It should also be noted that from the heater to the window, the temperature also differs by 5-10 degrees, or even more.

Airing

This seemingly simple and understandable procedure, when examined in detail, brings significant changes to our air that we create in the room. When airing, not only the air in the room is cleaned, but also an intensive exchange of heat and moisture occurs, and after airing, all our efforts to create optimal air can be nullified.

But it is also impossible without ventilation, so in the practical part we will discuss how to perform 3 important procedures: ventilation, thermoregulation, moisture regulation, without compromising other air parameters.

In fact, in our rooms there is a constant exchange of air with the external environment (unless, of course, your room is hermetically sealed and neither windows nor doors are ever opened), in some rooms there is more, and in some less. For this, there are even special measurements of how many times the air per hour is completely updated. If 1 is one time, if 2 is two times, and if 0.5 then only half of the air is updated per hour. If you have all windows and doors closed, then for your room this indicator is close to 0.1, and if you have everything open, then the indicator is close to 3-4.

With a sick child, this indicator should preferably be at least 1. But this is in winter time very difficult, since humidifiers can’t manage to humidify the entire room in an hour (we are getting ahead of ourselves again).

Part 2 - Practice

Now let's move from theory to practice. The recipes given here try to teach you to think creatively about living conditions, and adapt them to your needs and conditions.

Our goal

Under any conditions outside the window, provide yourself and your child with optimal air parameters - about 18C and 50-70% humidity (or in an average room have about 500-700 grams of water evaporated in the air). With minimum effort, minimum cost and maximum convenience. By priority:

• air quality comes first
• air temperature in second place
• air humidity in third place

General

The effect on air can be divided into 2 parts:

• active correction to achieve optimal parameters
• passive maintenance of optimal air parameters

That is, first we actively turn on all the forces at full power to achieve optimal air parameters as quickly as possible, and then reduce the influence to the minimum necessary to maintain optimal air parameters.

Tools

To influence the air, we have the following tools:

Air conditioner

• cost: high
• temperature: cooling high
• humidity: dry
• ventilation: low
• noise: low
• service: rare
• mobility: no

Evaporative cooler

• cost: low
• temperature: cooling normal
• humidity: high humidification
• ventilation: high
• noise: medium
• maintenance: daily
• mobility: high

ultrasonic humidifier

• cost: low
• temperature: not affected
• humidity: medium humidity
• ventilation: none
• noise: very low
• maintenance: daily
• mobility: high

stove/battery

• cost: moderate
• temperature: warm
• humidity: dry
• ventilation: none
• noise: very low
• service: rare
• mobility: no

Air purifier/sink

• cost: high
• temperature: not affected
• humidity: medium humidity
• ventilation: none but cleans the air with filters
• noise: very low
• maintenance: daily
• mobility: high

Fan

• cost: low
• temperature: not affected
• humidity: not affected
• ventilation: high
• noise: medium
• service: rare
• mobility: high

steam generator

• cost: medium
• temperature: slightly warm
• humidity: moisturizing moderately
• ventilation: none
• noise: low
• maintenance: daily
• mobility: high

In this part, we will begin to practically apply our knowledge in the struggle for optimal air parameters.

Room approach

The room approach to providing air is a fairly common method, it teaches us how to make the right air in the room. And for a start it is necessary to study such approach too.

autumn and spring in general, nothing needs to be done, just open the windows, the air is normal during the day, and cool humid at night, everything is ventilated and without cost, without effort.

BUT summer a big problem refrigerate it, as moisture is fine. For cooling, the most effective is air conditioning, but it is very expensive. And if you can afford it, then having at least 1 air conditioner does not even hurt, because cool air is critical in many diseases, and in summer it can be a salvation from the heat.

An alternative to an air conditioner is an evaporative cooler (for this device, a separate article, link below). The cooling power does not reach the air conditioner by several degrees, but it is quite sufficient to save from the heat, and its very strong plus is that it immediately humidifies the room, and also ventilates, and is very economical, and costs several times less than the air conditioner.

in winter everything is much more complicated, we are dealing with dry cold air. And inside the room, thanks to uncontrolled heating, it is dry and hot. By opening the window, you can still cool the room, but moisturizing it is a big problem. Of course, you have probably read how to turn off the heating, install a regulator, close windows, use an ultrasonic humidifier, etc. And if you do all this and you have no problems, then congratulations. Although you will still have some problems with ventilation, you generally cope well with the winter.

But here I would like to talk about an alternative method of air regulation. This is again the previously mentioned Evaporative Cooler. The peculiarity of the operation of this device is that the hotter and drier the air, the more efficiently it humidifies it and forms an almost stable temperature of 18-23C at the outlet (the exact temperature depends on the power of the device and the heat / dryness of the air). And if such a cooler is placed next to the heater, then it will draw all the hot air into itself and release cooled moist air.

The most important device requires open windows(or at least a window) so that excess moisture flies away. So by balancing the heater, the evaporative cooler, and opening the window, you can make the heat and moisture exchange in winter so that you have cool, humid and ventilated air in your apartment.

Of course, depending on your room, the location of the heating, the windows, and the model of the evaporative cooler, you will have to arrange air exchange in different ways. There are no universal formulas, but if you experiment a little and measure temperature and humidity at different angles, then through trial and error you will find your optimum.

So all you need is an evaporative cooler, and if possible, an air conditioner. Of course, no one forbids you to have an ordinary ultrasonic humidifier.

Personal approach

This approach is not very common among climate techniques. It is not aimed at organizing optimal air throughout the room, but to organize it exactly where it is needed, that is, under the nose of the child (and parents). In principle, it is not necessary for us that there is optimal air near the closet or bedside table, we need the right air under the child’s nose, and what happens in the other corners of the room is not important.

It should be clear from the description that this is a very economical method. And mostly we are talking about the air during sleep. We don't need measurements in different points rooms in order to maintain optimal air parameters throughout the room, and you only need to measure close to the child (and parents).

Spring, autumn, summer this approach is almost no different from the room approach. But winter there are differences (there are also differences when the child is sick). Suppose that you do not have the means and opportunities to isolate the heating, install a regulator, buy an evaporative cooler, etc., but you need to arrange optimal air for the child. Then you will need any cheap humidifier (you can find it for $10-30), the heating works, open the window so that the temperature balances somewhere between the window and the heating at the desired 18C (if it gets colder, then cover the window, and if it gets hot, then open it a little window, find a balance where the incoming cold from the window is compensated by the heat from the heating). Put a baby bed between the heating and the window where the air is balanced at 18C, this is usually 2-3 meters from the window. And if you put a hat right under the window, it is better to put on a hat for a child, because up to 50% of the heat leaves the head, and cold winds on the head will not do any good. Place a humidifier nearby so that the mist from the humidifier reaches the desired percentage of moisture to the child’s nose. This usually happens within a radius of a meter, and if a cheap humidifier, then half a meter.

And here you get desired temperature, and humidity and ventilation even in winter and at almost no cost.

If you want to arrange optimal air for yourself, then also lie down next to the child, where the desired temperature is reached and the humidifier works. Well, or another such humidifier you put yourself.

To find a balance, also do not forget about the height of the child, remember in theory, the higher, the warmer, the lower, the colder.

Also, regardless of the method of providing air, remember that optimal air should go directly into the child’s nose, and if you cover the child’s nose with a blanket, he will breathe warm air from under the blanket and all the work to provide air will lose its meaning. Therefore, it is best to dress the top of the child warmer and close the blanket to the waist / chest.

Olga Rogacheva
Experiments with air

Experience #1

Target experience air We need air to breathe. We inhale and exhale air.

move: Take a glass of water, insert a straw and exhale air. Bubbles appear in the glass.

Experience No. 2

Target experience: Lead children to understanding and meaning air

move: Make a small parachute. Show that when the parachute goes down, air a dome is bursting under it, supporting! it, so the decrease occurs smoothly.

Experience No. 3

Target experience: Lead children to understand the characteristics air. Air is invisible, has no definite shape, spreads in all directions, has no odor of its own.

move: Take scented napkins, orange peels, etc. and invite the children to smell the smells in the room in succession.

Experience No. 4

Target experience: Lead children to understand weight air. Air has weight. move:Put on the scales inflated and not inflated balloons: a bowl with an inflated balloon will outweigh

Experience No. 5

move: Put an open plastic bottle in the refrigerator. When it is cool enough, put an uninflated balloon on its neck. Then, put the bottle in a bowl of hot water. Watch the balloon inflate on its own. This happens because air expands when heated. Now put the bottle back in the fridge. The ball will then descend as air shrinks when cooled.

Experience No. 6

Target experience: Help identify property air(resilience, understand how force can be used air(traffic).

move: The teacher invites the children to spend balloon experience: see how it will fly if you untie the thread that holds it in air. Children with the help of a teacher inflate Balloon, release it and pay attention to the trajectory and duration of its flight. They find out that in order for the balloon to fly longer, it is necessary to inflate it more.

Experience No. 7

Target: Learn to reflect existing ideas in transformative activities. How can you play with the wind.

move: Take a square sheet of paper and cut it along pre-drawn lines. The corners are bent to the center, where they are attached to the stick with a pin, after placing a small bead between the turntable and the stick. In order for the spinner to fulfill its function in calm weather, it is necessary to run with a stick in hand. The spinner only spins when there is wind.

Experience No. 8

Target: Help bring out what is warm air lighter than cold and rises.

move: The teacher invites the children to compare the temperature air in the room and near warm objects. Determine where warmer: on the floor or on the couch? The teacher keeps the thermometer on the floor and then on the couch. Children are convinced that the higher, the warmer. Next, the teacher offers to approach the battery. Stretch your hand above the battery, below the battery. Where is warmer (Warmer above the battery.)

Then the teacher offers to go to the kettle with hot water. Raise your hand and hold it above the water. Children are convinced that water vapor is hot. Warm air is lighter than cold. Warm the air rises so the top is warmer.

Heating any medium, such as water or air, causes it to expand and become lighter. Conversely, cooling causes it to shrink and become heavier. The combination of these multidirectional physical influences forms a phenomenon called convection, which is one of the processes of heat transfer in large volumes of liquids and gases.

When a vessel of water is placed over a working burner, the water above the flame absorbs the energy. This energy causes the water molecules to move away from each other, causing it to become less dense. Heated water rises; in the figure, the gray paint on the bottom of the vessel makes this movement visible. At the same time, colder, denser water sinks down to take the place of the warm water that rises up. When warm water rises, it gives up some of its energy to the surrounding water and cools down a bit. Meanwhile, warmer water continues to rise, pushing layers of cooler water aside. Convection will stop only when the flame goes out and all the water has the same temperature.

Convection with the addition of heat

Heating the bottom of the tube increases the temperature of the lower layers of water. As a result, warm water rises, while heavier cold water sinks and also heats up. Over time, all water becomes hot. Heating the upper part of the test tube leads to an increase in the temperature of only the upper layers of water, since the lighter hot water remains above the cold one.

Convective movement of water

Rising from the bottom of a vessel on fire, heated water gradually loses heat. Once on the surface, this water diverges to the sides under the action of a rising column of warmer water. As the water cools, it becomes denser and sinks down.

Convection in a gaseous medium

Smoke wisps make it possible to trace the formation of convective currents in the air of the room (figures above). The process begins with warm air rising up (left figure). Having reached the ceiling (middle figure), this air diverges to the sides under the action of rising warmer air jets, after which, having lost heat, it falls down to the floor and, under the action of cooled air jets descending from above (figure on the right), again moves to the heat source, heats up and rises up.

Heating and cooling the air in the room

An air conditioner cools a room most effectively when placed near the ceiling (top picture below text), as the cooled air (blue in the picture) sinks down and then spreads through the room by convection. Conversely, the air heater works best when placed near the floor (bottom picture). Warm air (orange in the picture) rises and then circulates around the room.