How many kilograms of air in 1 m3. What is the density of air and what is it equal to under normal conditions? Air weight and factors that affect it

The main physical properties air: air density, its dynamic and kinematic viscosity, specific heat capacity, thermal conductivity, thermal diffusivity, Prandtl number and entropy. The properties of air are given in tables depending on the temperature at normal atmospheric pressure.

Air density versus temperature

A detailed table of dry air density values at various temperatures and normal atmospheric pressure is presented. What is the density of air? The density of air can be analytically determined by dividing its mass by the volume it occupies. under given conditions (pressure, temperature and humidity). It is also possible to calculate its density using the ideal gas equation of state formula. For this you need to know absolute pressure and air temperature, as well as its gas constant and molar volume. This equation allows you to calculate the density of air in a dry state.

On practice, to find out what is the density of air at different temperatures, it is convenient to use ready-made tables. For example, the given table of density values atmospheric air depending on its temperature. The air density in the table is expressed in kilograms per cubic meter and is given in the temperature range from minus 50 to 1200 degrees Celsius at normal atmospheric pressure (101325 Pa).

Air density depending on temperature - table

t, °С	ρ, kg / m 3	t, °С	ρ, kg / m 3	t, °С	ρ, kg / m 3	t, °С	ρ, kg / m 3
-50	1,584	20	1,205	150	0,835	600	0,404
-45	1,549	30	1,165	160	0,815	650	0,383
-40	1,515	40	1,128	170	0,797	700	0,362
-35	1,484	50	1,093	180	0,779	750	0,346
-30	1,453	60	1,06	190	0,763	800	0,329
-25	1,424	70	1,029	200	0,746	850	0,315
-20	1,395	80	1	250	0,674	900	0,301
-15	1,369	90	0,972	300	0,615	950	0,289
-10	1,342	100	0,946	350	0,566	1000	0,277
-5	1,318	110	0,922	400	0,524	1050	0,267
0	1,293	120	0,898	450	0,49	1100	0,257
10	1,247	130	0,876	500	0,456	1150	0,248
15	1,226	140	0,854	550	0,43	1200	0,239

At 25°C, air has a density of 1.185 kg/m 3 . When heated, the density of air decreases - the air expands (its specific volume increases). With an increase in temperature, for example, up to 1200°C, a very low air density is achieved, equal to 0.239 kg/m 3 , which is 5 times less than its value at room temperature. In general, the decrease in heating allows a process such as natural convection to take place and is used, for example, in aeronautics.

If we compare the density of air with respect to, then air is lighter by three orders of magnitude - at a temperature of 4 ° C, the density of water is 1000 kg / m 3, and the density of air is 1.27 kg / m 3. It is also necessary to note the value of air density at normal conditions. Normal conditions for gases are those under which their temperature is 0 ° C, and the pressure is equal to normal atmospheric pressure. Thus, according to the table, air density under normal conditions (at NU) is 1.293 kg / m 3.

Dynamic and kinematic viscosity of air at different temperatures

When performing thermal calculations, it is necessary to know the value of air viscosity (viscosity coefficient) at different temperatures. This value is required to calculate the Reynolds, Grashof, Rayleigh numbers, the values of which determine the flow regime of this gas. The table shows the values of the coefficients of dynamic μ and kinematic ν air viscosity in the temperature range from -50 to 1200°C at atmospheric pressure.

The viscosity of air increases significantly with increasing temperature. For example, the kinematic viscosity of air is equal to 15.06 10 -6 m 2 / s at a temperature of 20 ° C, and with an increase in temperature to 1200 ° C, the viscosity of the air becomes equal to 233.7 10 -6 m 2 / s, that is, it increases 15.5 times! The dynamic viscosity of air at a temperature of 20°C is 18.1·10 -6 Pa·s.

When air is heated, the values of both kinematic and dynamic viscosity increase. These two quantities are interconnected through the value of air density, the value of which decreases when this gas is heated. An increase in the kinematic and dynamic viscosity of air (as well as other gases) during heating is associated with a more intense vibration of air molecules around them. equilibrium state(according to MKT).

Dynamic and kinematic viscosity of air at different temperatures - table

t, °С	μ 10 6 , Pa s	ν 10 6, m 2 / s	t, °С	μ 10 6 , Pa s	ν 10 6, m 2 / s	t, °С	μ 10 6 , Pa s	ν 10 6, m 2 / s
-50	14,6	9,23	70	20,6	20,02	350	31,4	55,46
-45	14,9	9,64	80	21,1	21,09	400	33	63,09
-40	15,2	10,04	90	21,5	22,1	450	34,6	69,28
-35	15,5	10,42	100	21,9	23,13	500	36,2	79,38
-30	15,7	10,8	110	22,4	24,3	550	37,7	88,14
-25	16	11,21	120	22,8	25,45	600	39,1	96,89
-20	16,2	11,61	130	23,3	26,63	650	40,5	106,15
-15	16,5	12,02	140	23,7	27,8	700	41,8	115,4
-10	16,7	12,43	150	24,1	28,95	750	43,1	125,1
-5	17	12,86	160	24,5	30,09	800	44,3	134,8
0	17,2	13,28	170	24,9	31,29	850	45,5	145
10	17,6	14,16	180	25,3	32,49	900	46,7	155,1
15	17,9	14,61	190	25,7	33,67	950	47,9	166,1
20	18,1	15,06	200	26	34,85	1000	49	177,1
30	18,6	16	225	26,7	37,73	1050	50,1	188,2
40	19,1	16,96	250	27,4	40,61	1100	51,2	199,3
50	19,6	17,95	300	29,7	48,33	1150	52,4	216,5
60	20,1	18,97	325	30,6	51,9	1200	53,5	233,7

Note: Be careful! The viscosity of air is given to the power of 10 6 .

Specific heat capacity of air at temperatures from -50 to 1200°С

A table of the specific heat capacity of air at various temperatures is presented. The heat capacity in the table is given at constant pressure (isobaric heat capacity of air) in the temperature range from minus 50 to 1200°C for dry air. What is the specific heat capacity of air? The value of specific heat capacity determines the amount of heat that must be supplied to one kilogram of air at constant pressure to increase its temperature by 1 degree. For example, at 20°C, to heat 1 kg of this gas by 1°C in an isobaric process, 1005 J of heat is required.

The specific heat capacity of air increases as its temperature rises. However, the dependence of the mass heat capacity of air on temperature is not linear. In the range from -50 to 120°C, its value practically does not change - under these conditions, the average heat capacity of air is 1010 J/(kg deg). According to the table, it can be seen that the temperature begins to have a significant effect from a value of 130°C. However, air temperature affects its specific heat capacity much weaker than its viscosity. So, when heated from 0 to 1200°C, the heat capacity of air increases only 1.2 times - from 1005 to 1210 J/(kg deg).

It should be noted that the heat capacity humid air higher than dry. If we compare air, it is obvious that water has a higher value and the water content in the air leads to an increase in specific heat.

Specific heat capacity of air at different temperatures - table

t, °С	C p , J/(kg deg)	t, °С	C p , J/(kg deg)	t, °С	C p , J/(kg deg)	t, °С	C p , J/(kg deg)
-50	1013	20	1005	150	1015	600	1114
-45	1013	30	1005	160	1017	650	1125
-40	1013	40	1005	170	1020	700	1135
-35	1013	50	1005	180	1022	750	1146
-30	1013	60	1005	190	1024	800	1156
-25	1011	70	1009	200	1026	850	1164
-20	1009	80	1009	250	1037	900	1172
-15	1009	90	1009	300	1047	950	1179
-10	1009	100	1009	350	1058	1000	1185
-5	1007	110	1009	400	1068	1050	1191
0	1005	120	1009	450	1081	1100	1197
10	1005	130	1011	500	1093	1150	1204
15	1005	140	1013	550	1104	1200	1210

Thermal conductivity, thermal diffusivity, Prandtl number of air

The table shows such physical properties of atmospheric air as thermal conductivity, thermal diffusivity and its Prandtl number depending on temperature. The thermophysical properties of air are given in the range from -50 to 1200°C for dry air. According to the table, it can be seen that these properties of air significantly depend on temperature and temperature dependence considered properties of this gas is different.

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

Experience can prove that air has weight. In the middle of a stick sixty centimeters long, we will strengthen the rope, and we will tie two identical ropes to both ends of it. balloons. Let's hang the stick by the string and see that it hangs horizontally. If you now pierce one of the inflated balloons with a needle, 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, then the stick will again take a horizontal position.

This is because the air in the inflated balloon denser, which means that 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 Atmosphere pressure. Like all objects around us, air is also subject to gravity. This is what 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.

An air column 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 straight, on his head and shoulders, the area of \u200b\u200bwhich is approximately 250 cm 2!

We would not be able to withstand such a weight if it were not opposed by the same pressure inside our body. The following experience will help us understand this. If you stretch a paper sheet with both hands and someone presses a finger on it from one side, then the result will be the same - a hole in the paper. But if you press two index fingers on the same place, but from 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 he cannot crush us, because the counter pressure of the body is equal to the external one.
The simple experience depicted above makes this clear:
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 air, and therefore we neglect its weight, since the weight of air in air is zero. For example, if we weigh an empty glass flask, we will consider the result obtained as the weight of the flask, neglecting the fact that it is filled with air. But if the flask is closed hermetically 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 what kind of load is the air that your room contains? A few grams or a few kilograms? Are you able to lift such a load with one finger, or would you barely keep 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 cannot say how much a certain volume of air weighs.

Remember that a liter mug of air of the density that it has near earth's surface at normal room temperature, it 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. It is now easy 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 m 2 and a height of 4 m. In such a room there are 40 cubic meters of air, which weighs, therefore, forty times 1.2 kg. This will be 48 kg.

So, even in such a small room, the air weighs a little less than yourself. It would not be easy for you to carry such a load on your shoulders. And the air of a room twice as large, loaded onto your back, could crush you.

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

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HOW MANY? Even before she began studying uranium rays, Maria had already decided that prints on photographic films were an inaccurate method of analysis, and she wanted to measure the intensity of the rays and compare the amount of radiation emitted various substances. She knew: Becquerel

Air is an intangible quantity, it is impossible to feel it, smell it, it is everywhere, but for a person it is invisible, it is not easy to find out how much air weighs, but it is possible. If the surface of the Earth, as in a children's game, is drawn into small squares, 1x1 cm in size, then the weight of each of them will be 1 kg, that is, 1 cm 2 of the atmosphere contains 1 kg of air.

Can it be proven? Quite. If you build a scale from an ordinary pencil and two balloons, fixing the design on the thread, the pencil will be in balance, since the weight of the two inflated balls is the same. It is worth piercing one of the balls, the advantage will be in the direction of the inflated ball, because the air from the damaged ball has come out. Accordingly, a simple physical experience proves that air has a certain weight. But if we weigh the air flat surface and in the mountains, then its mass will be different - the mountain air is much lighter than the one we breathe near the sea. reasons different weight several:

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 exactly by half, which can cause dizziness, nausea and ear pain;
water content in the air.

The composition of 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 number of ingredients in the composition of air can change and, accordingly, the mass of air also undergoes changes in the direction of increase or decrease.

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

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

How much does a cube of air weigh?

At a temperature equal to 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 palpable enough, why doesn't a person feel heaviness? Such physical phenomenon, as atmospheric pressure, implies that an air column weighing 250 kg presses on each inhabitant of the planet. The area of the palm of an adult, on average, is 77 cm 2. 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. AT real life even a weightlifter cannot do this, however, each of us can easily cope with such a load, because atmospheric pressure presses from both sides, both outside the human body and from the inside, that is, the difference is ultimately equal to zero.

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

Knowing these physical quantities, it is possible to calculate the mass of the Earth's atmosphere - the amount of air that is held in near-Earth space by gravity. The upper boundary of the atmosphere ends at a height of 118 km, that is, knowing the weight of m 3 of air, you can divide the entire borrowed surface into air columns, with a base of 1x1m, and add up the resulting mass of such columns. Ultimately, it will be equal to 5.3 * 10 to the fifteenth degree of tons. The weight of the planet's air armor is quite large, but even it is only one millionth of the total mass. the globe. The Earth's atmosphere serves as a kind of buffer that keeps the Earth from unpleasant cosmic surprises. From only one solar storms that reach the surface of the planet, the atmosphere loses up to 100 thousand tons of its mass per year! Such an invisible and reliable shield is 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 is broadcast daily on a 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 vital 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 occur in liquid form. For the transition of a substance into a given state of aggregation will require exposure to enormous pressure and very low temperatures. Astronomers suggest that there are planets whose surface is 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 houseplants in an apartment are not just an interior item, they purify the air in the room, the pollution of which is ten times higher than on the street.

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

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

For a person, air cleanliness is also very important, so after working in the office, doctors recommend taking daily one-hour walks in the park, forest, and outside the city. After such "air" therapy, vitality the body is restored and well-being improves significantly. The recipe for this free and effective medicine has been known since ancient times, many scientists, rulers considered daily walks in the fresh air to be an obligatory ritual.

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