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 attach a rope, and we will tie two identical balloons to both ends. 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 with two index fingers on 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...

Physics at every step Perelman Yakov Isidorovich

How much does the air in the room weigh?

Can you say at least approximately how much weight the air contained in your room represents? A few grams or a few kilograms? Are you able to lift such a load with one finger, or would you barely be able to hold it on your shoulders?

Now, perhaps, there are no longer people who think, as the ancients believed, that air weighs nothing at all. But even now many people will not be able to say how much a certain volume of air weighs.

Remember that a liter mug of air of the same density as it has nearby earth's surface with normal room temperature, weighs about 1.2 g. Since a cubic meter contains 1 thousand liters, a cubic meter of air weighs a thousand times more than 1.2 g, namely 1.2 kg. Now it is not difficult to answer the question posed earlier. To do this, you just need to find out how many cubic meters are in your room, and then the weight of the air contained in it will be determined.

Let the room have an area of ​​10 m2 and a height of 4 m. In such a room there are 40 cubic meters of air, which weighs forty times 1.2 kg. This will be 48 kg.

So, even in such a small room, the air weighs a little less than you. You would be able to carry such a load on your shoulders with difficulty. And the air of a room twice as spacious, loaded onto your back, could crush you.

This text is an introductory fragment. From the book The Newest Book of Facts. Volume 3 [Physics, chemistry and technology. History and archaeology. Miscellaneous] author Kondrashov Anatoly Pavlovich

From the book The History of Candles author Faraday Michael

From the book Five Unsolved Problems of Science by Wiggins Arthur

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From the book NIKOLA TESLA. LECTURES. ARTICLES. by Tesla Nikola

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Many may be surprised by the fact that air has a certain non-zero weight. Exact value This weight is not so easy to determine, since it is greatly influenced by factors such as chemical composition, humidity, temperature and pressure. Let's take a closer look at the question of how much air weighs.

What is air

Before answering the question of how much air weighs, it is necessary to understand what this substance is. Air is gas envelope, which exists around our planet, and which is a homogeneous mixture of various gases. Air contains the following gases:

  • nitrogen (78.08%);
  • oxygen (20.94%);
  • argon (0.93%);
  • water vapor (0.40%);
  • carbon dioxide (0.035%).

In addition to the gases listed above, the air also contains minimum quantities neon (0.0018%), helium (0.0005%), methane (0.00017%), krypton (0.00014%), hydrogen (0.00005%), ammonia (0.0003%).

It is interesting to note that these components can be separated by condensing air, that is, turning it into a liquid state by increasing pressure and decreasing temperature. Since each component of air has its own condensation temperature, in this way it is possible to isolate all components from the air, which is used in practice.

Air weight and factors that affect it

What prevents you from answering exactly the question of how much a cubic meter of air weighs? Of course, there are a number of factors that can greatly influence this weight.

Firstly, this is the chemical composition. The above data is for the composition of clean air, however, currently this air in many places on the planet is heavily polluted, and accordingly, its composition will be different. Thus, near large cities the air contains more carbon dioxide, ammonia, and methane than the air in rural areas.

Secondly, humidity, that is, the amount of water vapor contained in the atmosphere. The more wet air, the less it weighs, other things being equal.

Thirdly, temperature. This is one of the important factors; the lower its value, the higher the air density, and, accordingly, the greater its weight.

Fourthly, atmospheric pressure, which directly reflects the number of air molecules in a certain volume, that is, its weight.

To understand how the combination of these factors affects the weight of air, let's give a simple example: the mass of one meter of cubic dry air at a temperature of 25 ° C, located near the surface of the earth, is 1.205 kg, if we consider a similar volume of air near the surface of the sea at a temperature of 0 ° C, then its mass will already be equal to 1.293 kg, that is, it will increase by 7.3%.

Change in air density with altitude

As altitude increases, air pressure drops, and its density and weight decrease accordingly. Atmospheric air at the pressures observed on Earth can, to a first approximation, be considered an ideal gas. This means that pressure and air density are mathematically related to each other through the equation of state of an ideal gas: P = ρ*R*T/M, where P is pressure, ρ is density, T is temperature in kelvins, M is molar mass of air, R is the universal gas constant.

From the above formula, you can obtain a formula for the dependence of air density on height, taking into account that the pressure changes according to the law P = P 0 +ρ*g*h, where P 0 is the pressure at the surface of the earth, g is the acceleration of gravity, h is the height . Substituting this formula for pressure into the previous expression and expressing the density, we obtain: ρ(h) = P 0 *M/(R*T(h)+g(h)*M*h). Using this expression, you can determine the density of air at any altitude. Accordingly, the weight of air (it would be more correct to say mass) is determined by the formula m(h) = ρ(h)*V, where V is the given volume.

In the expression for the dependence of density on height, it can be noted that temperature and gravitational acceleration also depend on height. The last dependence can be neglected if we're talking about about altitudes no more than 1-2 km. As for temperature, its dependence on height is well described by the following empirical expression: T(h) = T 0 -0.65*h, where T 0 is the air temperature near the earth's surface.

In order not to constantly calculate the density for each altitude, below we provide a table of the dependence of the main characteristics of air on altitude (up to 10 km).

Which air is the heaviest

By considering the main factors that determine the answer to the question of how much air weighs, you can understand which air will be the heaviest. In short, cold air always weighs more than warm air, since the density of the latter is lower, and dry air weighs more than humid air. The last statement is easy to understand, since it is 29 g/mol, and the molar mass of a water molecule is 18 g/mol, that is, 1.6 times less.

Determination of air weight under given conditions

Now let's decide specific task. Let's answer the question of how much air weighs, occupying a volume of 150 liters, at a temperature of 288 K. Let's take into account that 1 liter is a thousandth of a cubic meter, that is, 1 liter = 0.001 m 3. As for the temperature of 288 K, it corresponds to 15 ° C, that is, it is typical for many areas of our planet. Next you need to determine the air density. You can do this in two ways:

  1. Calculate using the above formula for an altitude of 0 meters above sea level. In this case, the value obtained is ρ = 1.227 kg/m 3
  2. Look at the table above, which was built based on T 0 = 288.15 K. The table contains the value ρ = 1.225 kg/m 3.

Thus, we have two numbers that agree well with each other. The slight difference is due to an error of 0.15 K in determining the temperature, and also to the fact that air is still not an ideal gas, but a real gas. Therefore, for further calculations, we will take the average of the two obtained values, that is, ρ = 1.226 kg/m 3.

Now, using the formula for the relationship between mass, density and volume, we get: m = ρ*V = 1.226 kg/m 3 * 0.150 m 3 = 0.1839 kg or 183.9 grams.

You can also answer how much a liter of air weighs under given conditions: m = 1.226 kg/m3 * 0.001 m3 = 0.001226 kg or approximately 1.2 grams.

Why don't we feel the air pressing on us?

How much does 1 m3 of air weigh? A little more than 1 kilogram. The entire atmospheric table of our planet puts pressure on a person with its weight of 200 kg! This is a fairly large mass of air that could cause a lot of trouble to a person. Why don't we feel it? This is explained by two reasons: firstly, there is also internal pressure within the person himself, which counteracts the external atmospheric pressure, secondly, air, being a gas, exerts pressure in all directions equally, that is, pressures in all directions balance each other.

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%).

The content of the components is practically independent of where in the world the dry air sample is 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 under 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, ethyl alcohol, diethyl ether and many gases easily turn into solids. 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 relative density the first gas over 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 mass of 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.

Compressed air is air under pressure greater than atmospheric pressure.

Compressed air is a unique energy carrier along with electricity, natural gas and water. In industrial settings, compressed air is mainly used to drive pneumatically driven devices and mechanisms (pneumatic drive).

In everyday, everyday life, we practically do not notice the Air around us. However, throughout human history, people have used unique properties air. The invention of the sail and the forge, the windmill and hot air balloon became the first steps in using air as an energy carrier.

With the invention of the compressor, the era of industrial use of compressed air began. And the question: “ What is Air and what properties does it have? - became far from idle.

When starting to design a new pneumatic system or modernize an existing one, it would be useful to remember about some properties of air, terms and units of measurement.

Air is a mixture of gases, mainly consisting of nitrogen and oxygen.

Air composition

Element*

Designation

By volume, %

By weight, %

Oxygen

Carbon dioxide

CO2

CH 4

H2O

The average relative molar mass is -28.98. 10 -3 kg/mol

*Air composition may vary. Typically, in industrial areas the air contains