Does air have weight? What is air density and what is it equal to under normal conditions? Air density depending on temperature.

Although we cannot feel the air around us, air is not nothing. Air is a mixture of gases: nitrogen, oxygen and others. And gases, like other substances, consist of molecules, and therefore have weight, although small.

Experiments can be used to prove that air has weight. In the middle of a stick about sixty centimeters long, we will strengthen a rope, and tie two identical ones to both ends balloon. Let's hang the stick by a string and see that it hangs horizontally. If you now pierce one of the inflated balloons with a needle, the air will come out of it, and the end of the stick to which it was tied will rise up. If you pierce the second ball, the stick will again take a horizontal position.

This happens because there is air in the inflated balloon. tighter, and therefore heavier than the one around it.

How much air weighs depends on when and where it is weighed. The weight of air above a horizontal plane is atmospheric pressure. Like all objects around us, air is also subject to gravity. It is this that gives the air a weight that is equal to 1 kg per square centimeter. The density of air is about 1.2 kg/m 3, that is, a cube with a side of 1 m filled with air weighs 1.2 kg.

A column of air rising vertically above the Earth stretches for several hundred kilometers. This means that a column of air weighing about 250 kg presses on a person standing upright, on his head and shoulders, the area of ​​which is approximately 250 cm 2!

We would not be able to withstand such a weight if it were not resisted by the same pressure inside our body. The following experience will help us understand this. If you stretch a sheet of paper with both hands and someone presses a finger on it on one side, the result will be the same - a hole in the paper. But if you press two index fingers to the same place, but with different sides, nothing will happen. The pressure on both sides will be the same. The same thing happens with the pressure of the air column and the counter pressure inside our body: they are equal.

Air has weight and presses on our body from all sides.
But it cannot crush us, because the counter pressure of the body is equal to the external one.
The simple experiment depicted above makes this obvious:
if you press your finger on a sheet of paper on one side, it will tear;
but if you press on it from both sides, this will not happen.

By the way...

In everyday life, when we weigh something, we do it in the air, and therefore we neglect its weight, since the weight of air in the air is zero. For example, if we weigh an empty glass flask, we will consider the result obtained to be the weight of the flask, neglecting the fact that it is filled with air. But if the flask is sealed and all the air is pumped out of it, we will get a completely different result...

DEFINITION

Atmospheric air is a mixture of many gases. Air has a complex composition. Its main components can be divided into three groups: constant, variable and random. The former include oxygen (the oxygen content in the air is about 21% by volume), nitrogen (about 86%) and the so-called inert gases (about 1%).

Content components practically does not depend on where globe a sample of dry air was taken. The second group includes carbon dioxide (0.02 - 0.04%) and water vapor (up to 3%). The content of random components depends on local conditions: near metallurgical plants, noticeable amounts of sulfur dioxide are often mixed into the air, in places where organic residues decompose - ammonia, etc. In addition to various gases, the air always contains more or less dust.

Air density is a value equal to the mass of gas in the Earth's atmosphere divided by a unit volume. It depends on pressure, temperature and humidity. There is a standard value for air density - 1.225 kg/m 3, corresponding to the density of dry air at a temperature of 15 o C and a pressure of 101330 Pa.

Knowing from experience the mass of a liter of air at normal conditions(1.293 g), we can calculate the molecular weight that air would have if it were an individual gas. Since a gram molecule of any gas occupies a volume of 22.4 liters under normal conditions, the average molecular weight of air is equal to

22.4 × 1.293 = 29.

This number - 29 - should be remembered: knowing it, it is easy to calculate the density of any gas relative to air.

Density of liquid air

When sufficiently cooled, the air turns into a liquid state. Liquid air can be stored for quite a long time in vessels with double walls, from the space between which the air is pumped out to reduce heat transfer. Similar vessels are used, for example, in thermoses.

Liquid air that evaporates freely under normal conditions has a temperature of about (-190 o C). Its composition is not constant, since nitrogen evaporates more easily than oxygen. As the nitrogen is removed, the color of the liquid air changes from bluish to pale blue (the color of liquid oxygen).

In liquid air they easily transform into solid state ethyl alcohol, diethyl ether and many gases. If, for example, carbon dioxide is passed through liquid air, it turns into white flakes similar in appearance. appearance to the snow. Mercury immersed in liquid air becomes hard and malleable.

Many substances cooled by liquid air dramatically change their properties. Thus, chink and tin become so brittle that they easily turn into powder, a lead bell makes a clear ringing sound, and a frozen rubber ball shatters if dropped on the floor.

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

Exercise	Determine how many times heavier than air is hydrogen sulfide H 2 S.
Solution	The ratio of the mass of a given gas to the mass of another gas taken in the same volume, at the same temperature and the same pressure is called the relative density of the first gas to the second. This value shows how many times the first gas is heavier or lighter than the second gas. The relative molecular weight of air is taken to be 29 (taking into account the content of nitrogen, oxygen and other gases in the air). It should be noted that the concept of “relative molecular weight air" is used conditionally, since air is a mixture of gases. D air (H 2 S) = M r (H 2 S) / M r (air); D air (H 2 S) = 34 / 29 = 1.17. M r (H 2 S) = 2 × A r (H) + A r (S) = 2 × 1 + 32 = 2 + 32 = 34.
Answer	Hydrogen sulfide H 2 S is 1.17 times heavier than air.

Air density is a physical quantity that characterizes the specific gravity of air under natural conditions or the mass of gas in the Earth's atmosphere per unit volume. The value of air density is a function of the height of the measurements taken, its humidity and temperature.

The air density standard is taken to be 1.29 kg/m3, which is calculated as the ratio of its molar mass(29 g/mol) to the molar volume, the same for all gases (22.413996 dm3), corresponding to the density of dry air at 0°C (273.15°K) and a pressure of 760 mm mercury(101325 Pa) at sea level (that is, under normal conditions).

Not long ago, information about air density was obtained indirectly through observations of auroras, the propagation of radio waves, and meteors. Since the advent of artificial Earth satellites, air density began to be calculated using data obtained from their braking.

Another method is to observe the spreading of artificial sodium vapor clouds created by weather rockets. In Europe, the air density at the Earth's surface is 1.258 kg/m3, at an altitude of five km - 0.735, at an altitude of twenty km - 0.087, at an altitude of forty km - 0.004 kg/m3.

There are two types of air density: mass and weight (specific gravity).

Weight density determines the weight of 1 m3 of air and is calculated by the formula γ = G/V, where γ is weight density, kgf/m3; G is the weight of air, measured in kgf; V is the volume of air, measured in m3. It has been established that 1 m3 of air under standard conditions(barometric pressure 760 mmHg, t=15°C) weighs 1.225 kgf, based on this, the weight density (specific gravity) of 1 m3 of air is equal to γ ​​= 1.225 kgf/m3.

It should be taken into account that air weight is a variable quantity and changes depending on various conditions, such as geographic latitude and the force of inertia that occurs when the Earth rotates around its axis. At the poles the weight of air is 5% greater than at the equator.

Mass density of air is the mass of 1 m3 of air, denoted Greek letterρ. As you know, body weight is a constant quantity. The unit of mass is considered to be the mass of a platinum iridide weight, which is located in the International Chamber of Weights and Measures in Paris.

Air mass density ρ is calculated using the following formula: ρ = m / v. Here m is the mass of air, measured in kg×s2/m; ρ is its mass density, measured in kgf×s2/m4.

The mass and weight densities of air depend on: ρ = γ / g, where g is the gravitational acceleration coefficient equal to 9.8 m/s². It follows that the mass density of air under standard conditions is 0.1250 kg×s2/m4.

As barometric pressure and temperature change, the density of the air changes. Based on the Boyle-Marriott law, the greater the pressure, the greater the air density. However, as pressure decreases with height, air density also decreases, which introduces its own adjustments, as a result of which the law of vertical pressure changes becomes more complex.

The equation that expresses this law of pressure change with height in an atmosphere at rest is called basic equation of statics.

It states that with increasing altitude the pressure changes downward and when rising to the same height, the decrease in pressure is greater, the more more power gravity and air density.

Changes in air density play an important role in this equation. As a result, we can say that the higher you rise, the less pressure will drop when rising to the same height. Air density depends on temperature as follows: in warm air the pressure decreases less intensely than in cold air, therefore, at the same height, the pressure in a warm air mass is higher than in a cold one.

With changing values ​​of temperature and pressure, the mass density of air is calculated by the formula: ρ = 0.0473xB / T. Here B is the barometric pressure, measured in mm of mercury, T is the air temperature, measured in Kelvin.

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Density is also determined by air humidity. The presence of water pores leads to a decrease in air density, which is explained by the low molar mass of water (18 g/mol) against the background of the molar mass of dry air (29 g/mol). Humid air can be considered as a mixture ideal gases, in each of which the combination of densities allows one to obtain the required density value for their mixture.

This kind of interpretation makes it possible to determine density values ​​with an error level of less than 0.2% in the temperature range from −10 °C to 50 °C. Air density allows you to obtain the value of its moisture content, which is calculated by dividing the density of water vapor (in grams) contained in the air by the density of dry air in kilograms.

The basic equation of statics does not allow us to solve constantly arising practical problems in the real conditions of a changing atmosphere. Therefore, it is solved under various simplified assumptions that correspond to the actual real conditions, by putting forward a number of particular assumptions.

The basic equation of statics makes it possible to obtain the value of the vertical pressure gradient, which expresses the change in pressure during ascent or descent per unit height, i.e., the change in pressure per unit vertical distance.

Instead of a vertical gradient, they often use its inverse value - the pressure level in meters per millibar (sometimes there is also an outdated version of the term “pressure gradient” - barometric gradient).

Low air density determines little resistance to movement. Many land animals have evolved to take advantage of the environmental benefits of this property. air environment, due to which they acquired the ability to fly. 75% of all species of land animals are capable of active flight. They are mostly insects and birds, but there are also mammals and reptiles.

Video on the topic “Determination of air density”

WHAT IS THE DENSITY OF AIR AT 150 DEGREES C (temperature Celsius), what is it equal to in different units kg/m3, g/cm3, g/ml, lb/m3. reference TABLE 1.

What is the density of air at 150 degrees Celsius in kg/m3, g/cm3, g/ml, lb/m3 . Do not forget that such a physical quantity, a characteristic of air, is its density in kg/m3 (the mass of a unit volume of atmospheric gas, where a unit of volume is taken to be 1 m3, 1 cubic meter, 1 cubic meter, 1 cubic centimeter, 1 cm3, 1 milliliter, 1 ml or 1 pound), depends on several parameters. Among the parameters describing the conditions for determining air density ( specific gravity air gas), I consider the following to be the most important and must be taken into account:

1. Temperature air gas.
2. Pressure at which the density of air gas was measured.
3. Humidity air gas or the percentage of water in it.

When any of these conditions change, the value of air density in kg/m3 (and therefore what its volumetric weight, what its specific gravity, what its volumetric mass) value will change within certain limits. Even if the other two parameters remain stable (do not change). Let me explain in more detail, for our case, when we want to find out what is the density of air at 150 degrees Celsius(in grams or kilograms). So, the air gas temperature is specified and selected by you in the request. So, in order to correctly describe how much density is in kg/m3, g/cm3, g/ml, lb/m3, we need to either indicate the second condition - the pressure at which it is measured. Or draw up a graph (table) that shows the change in density (specific gravity kg/m3, volumetric mass kg/m3, volumetric weight kg/m3) of air depending on the pressure created during the experiment.

If you are interested in the second case air density at T = 150 degrees C, then excuse me, but I have no desire to copy tabular data, a huge special reference book of air density at different pressure. I can’t yet decide on such a colossal amount of work, and I don’t see the need for it. See the reference book. Narrow profile information or rare special data, density values, must be sought in primary sources. It makes more sense.

It is more realistic, and probably more practical from our point of view, to indicate What is the density of air at 150 degrees Celsius, for a situation where the pressure is given by a constant and this is atmospheric pressure(under normal conditions - the most popular question). By the way, do you remember how much normal atmospheric pressure is? What is it equal to? Let me remind you that normal atmospheric pressure is considered to be 760 mmHg, or 101325 Pa (101 kPa), in principle these are normal conditions, adjusted for temperature. Meaning, what is the density of air in kg/m3 at a given temperature air gas you will see, find, recognize in table 1.

However, it must be said that the values ​​​​indicated in the table air density values ​​at 150 degrees in kg/m3, g/cm3, g/ml, will turn out to be true not for any atmospheric gas, but only for dry gas. As soon as we change the initial conditions and change the humidity of the air gas, it will immediately have different physical properties. And its density (weight of 1 cube of air in kilograms) at given temperature in degrees C (Celsius) (kg/m3) will also differ from the density of dry gas.

Reference table 1. What is the DENSITY OF AIR AT 150 DEGREES Celsius (C). HOW MUCH DOES 1 CUBE OF ATMOSPHERIC GAS WEIGH?(weight of 1 m3 in kilograms, weight of 1 cubic meter in kg, weight of 1 cubic meter of gas in g).

Air is an intangible quantity, it cannot be touched or smelled, it is everywhere, but for humans it is invisible; finding out how much air weighs is not easy, but possible. If the surface of the Earth, as in a children's game, is drawn into small squares measuring 1x1 cm, then the weight of each of them will be equal to 1 kg, that is, 1 cm 2 of atmosphere contains 1 kg of air.

Can this be proven? Quite. If you build a scale from an ordinary pencil and two balloons, having secured the structure to the thread, the pencil will be in balance, since the weight of the two inflated balls is the same. Once one of the balloons is pierced, the advantage will be in the direction of the inflated balloon, because the air from the damaged balloon has escaped. Accordingly, simple physical experience proves that air has some weight. But, if you weigh the air on a flat surface and in the mountains, then its mass will turn out to be different - mountain air is much lighter than the one we breathe near the sea. Reasons different weights some:

The weight of 1 m 3 of air is 1.29 kg.

• the higher the air rises, the more rarefied it becomes, that is, high in the mountains, the air pressure will not be 1 kg per cm 2, but half as much, but the content of oxygen necessary for breathing also decreases by exactly half, which can cause dizziness, nausea and ear pain;
• water content in the air.

The air mixture includes:

1.Nitrogen – 75.5%;

2. Oxygen – 23.15%;

3. Argon – 1.292%;

4. Carbon dioxide – 0,046%;

5. Neon – 0.0014%;

6. Methane – 0.000084%;

7. Helium – 0.000073%;

8. Krypton – 0.003%;

9. Hydrogen – 0.00008%;

10. Xenon – 0.00004%.

The amount of ingredients in the air may change and, accordingly, the mass of air also undergoes changes in the direction of increase or decrease.

• air always contains water vapor. The physical law is that the higher the air temperature, the more water it contains. This indicator is called air humidity and affects its weight.

What is the weight of air measured in? There are several indicators that determine its mass.

How much does a cube of air weigh?

At a temperature of 0° Celsius, the weight of 1 m 3 of air is 1.29 kg. That is, if you mentally allocate a space in a room with a height, width and length equal to 1 m, then this air cube will contain exactly this amount of air.

If air has weight and weight that is quite noticeable, why does a person not feel heaviness? This physical phenomenon, like atmospheric pressure, implies that every inhabitant of the planet is pressed by an air column weighing 250 kg. The average palm area of ​​an adult is 77 cm2. That is, in accordance with physical laws, each of us holds 77 kg of air in the palm of our hand! This is equivalent to the fact that we constantly carry 5 pound weights in each hand. IN real life Even a weightlifter cannot do this, however, each of us copes with such a load easily, because atmospheric pressure presses from both sides, both outside the human body and from the inside, that is, the difference is ultimately zero.

The properties of air are such that it affects the human body differently. High in the mountains, due to lack of oxygen, people experience visual hallucinations, and great depth, the combination of oxygen and nitrogen in a special mixture - “laughing gas” can create a feeling of euphoria and a feeling of weightlessness.

Knowing these physical quantities, you can calculate the mass of the Earth’s atmosphere - the amount of air that is held in near-Earth space forces of gravity. The upper boundary of the atmosphere ends at an altitude of 118 km, that is, knowing the weight of m 3 of air, you can divide the entire surface area into air columns, with a base of 1x1 m, and add up the resulting mass of such columns. Ultimately, it will be equal to 5.3 * 10 to the fifteenth power of tons. The weight of the planet's air armor is quite large, but it is only one millionth of total mass globe. The Earth's atmosphere serves as a kind of buffer that protects the Earth from unpleasant cosmic surprises. From solar storms alone that reach the surface of the planet, the atmosphere loses up to 100 thousand tons of its mass per year! So invisible and reliable shield- air.

How much does a liter of air weigh?

A person does not notice that he is constantly surrounded by transparent and almost invisible air. Is it possible to see this intangible element of the atmosphere? Visually, moving air masses broadcast daily on the television screen - warm or cold front brings long-awaited warming or heavy snowfall.

What else do we know about air? Probably, the fact that it is vitally necessary for all living beings living on the planet. Every day a person inhales and exhales about 20 kg of air, a quarter of which is consumed by the brain.

The weight of air can be measured in different physical quantities, including in liters. The weight of one liter of air will be equal to 1.2930 grams, at a pressure of 760 mm Hg. column and a temperature of 0°C. In addition to the usual gaseous state, air can also be found in liquid form. For the transition of a substance into a given physical state it will require exposure to enormous pressure and very low temperatures. Astronomers suggest that there are planets whose surfaces are completely covered with liquid air.

The sources of oxygen necessary for human existence are the Amazon forests, which produce up to 20% of this important element on the entire planet.

Forests are truly the “green” lungs of the planet, without which human existence is simply impossible. Therefore alive indoor plants in an apartment are not just a piece of furniture, they purify the indoor air, the pollution of which is tens of times higher than outside.

Clean air has long become a shortage in megacities; air pollution is so great that people are ready to buy clean air. “Air sellers” first appeared in Japan. They produced and sold clean air in cans, and any resident of Tokyo could open a can for dinner clean air, and enjoy its freshest aroma.

Air purity has a significant impact not only on human health, but also on animal health. In polluted areas of equatorial waters, near human-populated areas, dozens of dolphins are dying. The cause of death for mammals is a polluted atmosphere; in autopsies of animals, the lungs of dolphins resemble the lungs of miners, clogged with coal dust. The inhabitants of Antarctica, penguins, are also very sensitive to air pollution if the air contains large number harmful impurities, they begin to breathe heavily and intermittently.

For a person, clean air is also very important, so after working in the office, doctors recommend taking daily hour-long walks in the park, forest, or outside the city. After such “air” therapy, the body’s vitality is restored and well-being significantly improves. The recipe for this free and effective medicine has been known since ancient times; many scientists and rulers considered daily walks in the fresh air a mandatory ritual.

For a modern city dweller, air treatment is very relevant: a small portion of life-giving air, weighing 1-2 kg, is a panacea for many modern ailments!