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Air and not a lot of weight. Does air have weight and how much does it weigh? Why don't we feel the air pressing down on us

When we want to emphasize the lightness, almost "weightlessness" of something, we usually say "air", thereby emphasizing that the air seems to us to be something without weight. People have been sure of this for many centuries, and confidence was reinforced by the authority of such a respected scientist as Aristotle. This great ancient Greek philosopher once wondered if air had weight. As befits a scientist, he decided to test this in an experiment. On one side of the scales he placed a leather skinskin inflated with air, on the other - the exact same skinskin, only empty. The scales are balanced, therefore, the air weighs nothing!

Let's not judge strictly: at that time, physics was only in its infancy, and Aristotle, like any pioneer, could not avoid mistakes. To understand what the great scientist's mistake was, let's remember the exact meaning of the word "weight": the force with which the body acts on a support or suspension. What we call weight in everyday life and measure in kilograms is mass, the property of bodies to change their speed when a force is applied to them. It is not necessary to confuse these concepts: in weightlessness, bodies lose weight, not mass, so that in a spaceship the cabinet will hang in the air, but it will not be easier to move it from its place than on Earth. So, it is weight that is measured with the help of scales, but this weight corresponds to a certain mass, and since it is mass that interests us, for simplicity, we are talking about grams and kilograms, and not about Newtons, in which force is measured, but measured - that is precisely the force, it is precisely with the force that the error came out. When the leather waterskin was inflated, its volume increased, therefore, the buoyancy force of the surrounding air acting on it changed (the law of Archimedes, which had not yet been discovered at the time of Aristotle), so the scales were balanced.

G. Galileo went the other way. He weighed not a bag, but a hollow copper ball, which cannot change its volume. The researcher put it on the scales, and then pumped out the air from the balloon. And what? The ball has become lighter! This meant that the "weightless" air weighed!

At that time, such a statement could look extremely bold (it's no joke - to argue with Aristotle himself, whose views were "sanctified" by the authority of the Catholic Church!), But now we understand that this is logical. In order for a body to have weight (i.e., to act on a support), in essence, little is needed - for the force of gravity to act on it. It works on air. If this were not so, we would not have an atmosphere left, all the atoms of the gases that make it up would fly apart in outer space, therefore, the air also has a weight that acts on the earth's surface and everything that is on it. This weight is really small - a thimble of water, for example, weighs more than a liter of air, but ... there is a lot of it! If we take air from the earth's surface to the top of the atmosphere over an area of one square centimeter, this will be the weight corresponding to one kilogram. The area of the human palm is about 70 square centimeters, therefore, the air has such an effect on it as if we were holding an object weighing 70 kg in the palm of our hand! And on the human body as a whole, the air acts with a force corresponding to 15 tons, these are three five-ton trucks!

But we do not feel this heaviness for one simple reason: there is also air inside our body, and it acts with the same force, balancing the weight of the air outside. It cannot be otherwise, because our biological species originated on this planet, in the conditions of this atmosphere. But the atmosphere of Venus, for example, would crush us in no time!

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 balloons to both ends of it. 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 atmospheric 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 ...

City Scientific and Practical Conference

"Planet of the Erudites"

Does air have weight?

The world

4 "A" class, MBOU secondary school No. 14

Supervisor:

Dzerzhinsk

2013

2. Air cleaning.

3. Air has weight.

4. Conducting experiments.

Introduction

Our entire planet is shrouded in a transparent veil - air. We don't see it, we don't feel it. But if it suddenly disappears, water and all other liquids will instantly boil on Earth, and the rays of the Sun will burn all living things.

A person can go without food for five weeks, without water for five days, and without air for a maximum of five minutes. Air is needed by humans, animals, and plants to breathe, and therefore to live. And the wind? It's air movement! Without wind, clouds would always be above the sea or river. This means that rain without wind could only fall over water. Under the action of air and water, geological processes take place on the surface of the Earth, weather and climate are formed. By burning fuel (and oxygen, a component of air, must necessarily participate in this), people have long received heat, which is necessary both in everyday life and in production.

Air is the most important source of chemical raw materials. Just two centuries ago, scientists learned that air is a mixture of many gases, mainly oxygen and nitrogen, argon and carbon dioxide. Due to the urgency of this problem, we have identified the following purpose of the study: determine if air has weight?

Research objectives:

Review best practices on air science;

Determine the properties of air;

Conduct an experiment to determine the weight of air;

To conclude.

1. Importance of air for humans.

For a person, temperature, humidity, air movement are of great importance. For example, if you are lightly dressed and engaged in simple work, the best air temperature is 18-20 C. The harder the work, the lower the air temperature can be, but not so much that it becomes difficult to breathe, as in severe frost. People feel best when the air humidity is 40-60 percent. Dry air is usually well tolerated, and high air humidity has an unfavorable effect: at high temperatures, the body overheats, and at low temperatures, it becomes supercooled.

2. Air cleaning.

The amount of carbon dioxide, chemical compounds that are emitted by industrial enterprises and cars is growing in the air.

There is a widespread movement in the world in defense of nature. We have passed laws and are developing new ones, according to which the heads of enterprises are responsible for cleaning and neutralizing gases before they are released into the atmosphere.

Plants, the lungs of the planet, play a huge role in air purification. They trap dust, soot, absorb carbon dioxide and release oxygen. Among other natural filters, poplar and sunflower are the best at purifying air from pollution. Studies have shown that on busy highways, along which pyramidal poplars were planted and sunflower fields stretched, the air remained clean.

3. Air has weight.

Air has weight. In a liter bottle, for example, there is more than one gram of air. With its weight, the air presses on us and on all objects around us. If, for example, you pump out air from a tin can, it will flatten.

At a temperature of 0 °C and normal atmospheric pressure, the mass of air with a volume of 1 m3 is 1.29 kg.

4. Conducting experiments.

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

Another experience:

Get an empty clear plastic bottle. This experience will show whether it is as empty as it seems. Dip the bottle into the basin of water so that it begins to fill. See what happens to the water. You can see bubbles coming out of the neck. It is the water that displaces the air from the bottle. Most things that look empty are actually filled with air.

Feel the air

Is there air around? It's very easy to find out. Wave a piece of cardboard in front of your face. The cardboard will make the air move and you will feel it blow on your face.

Paper racing.

Air can move objects. We propose to arrange such a game: each player will need a piece of cardboard and a sheet of paper. One side of the sheet needs to be bent. Instead of finishing tape, stretch the thread. Now, on command, wave the cartons behind the sheets of paper, and the air will move them forward.

Heavy newspaper.

Take half a piece of newspaper and spread it out on the table. Place a ruler under the newspaper so that its end protrudes beyond the edge of the table. Click on the ruler and try to tear it off the table.

It turns out that this is not so easy to do, because air pressure presses the newspaper against the table.

Flattened package.

For the experiment, take a small juice bag with a hole for the tube. Suck out the juice from the bag through a straw. Keep pulling air through it. See what happens. When part of the air leaves the bag, the outside air will squeeze its walls. Take out the straw and look at the bag.

The walls parted again, because the air entered the bag and straightened it. See what happens to the bag if you blow even more air into it.

Thus, we have proved that air has weight.

Conclusion.

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. 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 / m3, that is, a cube with a side of 1 m, filled with air, weighs 1.2 kg.

By the way...

Bibliography

1. "Ecology, environment and man"

2. Encyclopedia "The World Around Us"

3. Website http://*****/

Many may be surprised by the fact that air has a certain non-zero weight. The exact value of this weight is not so easy to determine, since it is strongly influenced by factors such as chemical composition, humidity, temperature and pressure. Let us consider in more detail 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 a gas envelope that 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, 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 if air is condensed, that is, it is turned into a liquid state by increasing pressure and decreasing temperature. Since each component of the 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, a number of factors that can greatly influence this weight.

First, it is the chemical composition. Above are the data for the composition of clean air, however, at present this air is heavily polluted in many places on the planet, respectively, its composition will be different. Thus, near large cities, the air contains more carbon dioxide, ammonia, methane than the air in rural areas.

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

Third, temperature. This is one of the important factors, the smaller 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 take a simple example: the mass of one meter of dry cubic air at a temperature of 25 ° C, located near the surface of the earth, is 1.205 kg, if we consider the same volume of air near the sea surface 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 height

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

From the above formula, you can get the formula for the dependence of air density on height, given that the pressure changes according to the law P \u003d P 0 + ρ * g * h, where P 0 is the pressure at the earth's surface, g is the acceleration of gravity, h is the height . Substituting this formula for pressure into the previous expression, and expressing the density, we get: ρ(h) = P 0 *M/(R*T(h)+g(h)*M*h). Using this expression, you can determine the density of air at any height. Accordingly, the weight of air (more correctly, mass) is determined by the formula m(h) = ρ(h)*V, where V is a given volume.

In the expression for the dependence of density on height, one can notice that the temperature and acceleration of free fall also depend on height. The last dependence can be neglected if we are talking about heights of no more than 1–2 km. As for temperature, its dependence on altitude 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 present a table of the dependence of the main air characteristics 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 moist 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.

Determining the weight of air under given conditions

Now let's solve a specific problem. 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 regions of our planet. The next step is to determine the density of the air. You can do this in two ways:

Calculate using the above formula for an altitude of 0 meters above sea level. In this case, the value ρ \u003d 1.227 kg / m 3 is obtained
Look at the table above, which is built on the basis of T 0 \u003d 288.15 K. The table contains the value ρ \u003d 1.225 kg / m 3.

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

Now, using the formula for the relationship of mass, density and volume, we get: m \u003d ρ * V \u003d 1.226 kg / m 3 * 0.150 m 3 \u003d 0.1839 kg or 183.9 grams.

You can also answer how much a liter of air weighs under given conditions: m \u003d 1.226 kg / m 3 * 0.001 m 3 \u003d 0.001226 kg or approximately 1.2 grams.

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

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