Air pressure changes with altitude. Barometric formula. Pressure

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It is well known from the physics course that with increasing altitude above sea level, atmospheric pressure decreases. If up to an altitude of 500 meters no significant changes in this indicator are observed, then when reaching 5000 meters the atmospheric pressure decreases almost by half. As atmospheric pressure decreases, so does partial pressure oxygen in the air mixture, which immediately affects performance human body. The mechanism of this effect is explained by the fact that blood saturation with oxygen and its delivery to tissues and organs is carried out due to the difference in partial pressure in the blood and alveoli of the lungs, and at altitude this difference decreases.

Up to an altitude of 3500 - 4000 meters, the body itself compensates for the lack of oxygen entering the lungs by increasing breathing speed and increasing the volume of inhaled air (depth of breathing). Further climb for full compensation negative impact, requires use medicines and oxygen equipment (oxygen cylinder).

Oxygen is necessary for all organs and tissues human body during metabolism. Its consumption is directly proportional to the activity of the body. Lack of oxygen in the body can lead to the development of mountain sickness, which in extreme cases - swelling of the brain or lungs - can lead to death. Mountain sickness manifests itself in symptoms such as: headache, shortness of breath, rapid breathing, some have pain in the muscles and joints, decreased appetite, restless sleep, etc.

Altitude tolerance is a very individual indicator, determined by the characteristics of the body's metabolic processes and fitness.

An important role in combating the negative effects of altitude is played by acclimatization, during which the body learns to deal with the lack of oxygen.

• The body's first reaction to a decrease in blood pressure is an increase in heart rate, blood pressure and hyperventilation of the lungs, expansion of capillaries in the tissues occurs. Reserve blood from the spleen and liver is included in the blood circulation (7 - 14 days).

• The second phase of acclimatization consists of almost doubling the number of red blood cells produced by the bone marrow (from 4.5 to 8.0 million red blood cells per mm3 of blood), which leads to better tolerance to altitude.

The consumption of vitamins, especially vitamin C, has a beneficial effect at altitude.

2. Rototaev P. S. R79 Conquered giants. Ed. 2nd, revised and additional M., “Thought”, 1975. 283 p. from maps; 16 l. ill.

Atmosphere pressure is the pressure force of the air column per unit area. It is calculated in kilograms per 1 cm2 of surface, but since previously it was measured only with mercury manometers, it is conventionally customary to express this value in millimeters mercury(mmHg.). Normal atmospheric pressure is 760 mmHg. Art., or 1.033 kg/cm 2, which is considered to be one atmosphere (1 ata).

By doing individual species Work sometimes requires working at high or low atmospheric pressure, and these deviations from the norm are sometimes within significant limits (from 0.15-0.2 ata to 5-6 ata or more).

The effect of low atmospheric pressure on the body

As you rise to altitude, atmospheric pressure decreases: the higher you are above sea level, the lower the atmospheric pressure. So, at an altitude of 1000 m above sea level it is equal to 734 mm Hg. Art., 2000 m - 569 mm, 3000 m -526 mm, and at an altitude of 15000 m - 90 mm Hg. Art.

With reduced atmospheric pressure, there is increased and deepening of breathing, increased heart rate (their strength is weaker), a slight drop in blood pressure, and changes in the blood are also observed in the form of an increase in the number of red blood cells.

The adverse effect of low atmospheric pressure on the body is based on oxygen starvation. It is due to the fact that with a decrease in atmospheric pressure, the partial pressure of oxygen also decreases, therefore, with the normal functioning of the respiratory and circulatory organs, less oxygen enters the body. As a result, the blood is not sufficiently saturated with oxygen and does not fully deliver it to organs and tissues, which leads to oxygen starvation (anoxemia). Such changes occur more severely with a rapid decrease in atmospheric pressure, which happens during rapid takeoffs to high altitudes, when working on high-speed lifting mechanisms (cable cars, etc.). Rapidly developing oxygen starvation affects brain cells, which causes dizziness, nausea, sometimes vomiting, loss of coordination of movements, decreased memory, drowsiness; reduction of oxidative processes in muscle cells due to lack of oxygen, it is expressed in muscle weakness and rapid fatigue.

Practice shows that climbing to an altitude of more than 4500 m, where the atmospheric pressure is below 430 mm Hg, without oxygen supply for breathing is difficult to endure, and at an altitude of 8000 m (pressure 277 mm Hg) a person loses consciousness.

Blood, like any other liquid, upon contact with a gaseous medium (in this case in the alveoli of the lungs) dissolves a certain part of the gases - the higher their partial pressure, the greater the saturation of the blood with these gases. When atmospheric pressure decreases, partial pressure changes components air and, in particular, its main components - nitrogen (78%) and oxygen (21%); As a result, these gases begin to be released from the blood until the partial pressure equalizes. During a rapid decrease in atmospheric pressure, the release of gases, especially nitrogen, from the blood is so great that they do not have time to be removed through the respiratory system and accumulate in the blood vessels in the form of small bubbles. These gas bubbles can stretch tissue (even to the point of small tears), causing sharp pain, and in some cases, form gas clots in small vessels, impeding blood circulation.

The complex of physiological and pathological changes, arising as a result of a decrease in atmospheric pressure, is called altitude sickness, since these changes are usually associated with an increase in altitude.

Preventing altitude sickness

One of the widespread and effective measures to combat altitude sickness is the supply of oxygen for breathing when ascending to high altitudes (over 4500 m). Almost all modern aircraft flying on high altitude, and especially spaceships, are equipped with sealed cabins, where, regardless of the altitude and atmospheric pressure outside, the pressure is maintained constant at a level that fully ensures the normal condition of the flight crew and passengers. This is one of the radical solutions to this issue.

When performing physical and intense mental work in conditions of low atmospheric pressure, it is necessary to take into account the relatively rapid onset of fatigue, therefore periodic breaks should be provided, and in some cases, a shortened working day.

To work in conditions of low atmospheric pressure, the physically strongest persons, absolutely healthy, mainly men aged 20 - 30 years, should be selected. When selecting flight personnel, mandatory testing is required for the so-called altitude qualification tests in special chambers with reduced pressure.

Training and hardening play an important role in the prevention of altitude sickness. It is necessary to play sports, systematically perform one or another physical work. The diet of those working at low atmospheric pressure should be high-calorie, varied and rich in vitamins and mineral salts.

Helpful information:

Under the influence of gravity, the upper layers of air in the earth's atmosphere press on the underlying layers. This pressure, according to Pascal's law, is transmitted in all directions. The highest value is the pressure, called atmospheric, has near the surface of the Earth.

In a mercury barometer, the weight of a column of mercury per unit area (hydrostatic pressure of mercury) is balanced by the weight of the column atmospheric air per unit area - atmospheric pressure (see figure).

With increasing altitude above sea level, atmospheric pressure decreases (see graph).

Archimedean force for liquids and gases. Sailing conditions

A body immersed in a liquid or gas is acted upon by a buoyant force directed vertically upward and equal to the weight of the liquid (gas) taken in the volume of the immersed body.

Archimedes' formulation: a body loses exactly as much weight in a liquid as the weight of the displaced liquid.

The displacement force is applied at the geometric center of the body (for homogeneous bodies - at the center of gravity).

Under normal terrestrial conditions, a body located in a liquid or gas is subject to two forces: gravity and the Archimedean force. If the force of gravity is greater in magnitude than the Archimedean force, then the body sinks.

If the modulus of gravity is equal to the modulus of Archimedean force, then the body can be in equilibrium at any depth.

If the Archimedean force is greater in magnitude than the force of gravity, then the body floats up. The floating body partially protrudes above the surface of the liquid; the volume of the submerged part of the body is such that the weight of the displaced liquid is equal to the weight of the floating body.

Archimedean force is greater than gravity if the density of the liquid is greater than the density of the immersed body, and vice versa.

In a liquid, the pressure, as we know, is different levels varies and depends on the density of the liquid and the height of its column. Due to low compressibility, the density of the liquid at different depths is almost the same, Therefore, when calculating pressure, we consider its density constant and take into account only the change in level.

The situation is more complicated in gases. Gases are highly compressible. With what stronger gas compressed, the greater its density and the greater the pressure it produces. After all, gas pressure is created by the impacts of its molecules on the surface of the body.

The layers of air near the Earth's surface are compressed by all the layers of air above them. But the higher the layer of air is from the surface, the weaker it is compressed, the lower its density, and, consequently, the less pressure it produces. If, for example, balloon rises above the Earth's surface, then the air pressure on the ball becomes less not only because the height of the air column above it decreases, but also because the air density decreases - at the top it is less than at the bottom. Therefore, the dependence of air pressure on altitude is more complex; than the dependence of fluid pressure on the height of its column.

Observations show that atmospheric pressure in areas at sea level is on average 760 mm Hg. Art. The higher a place is above sea level, the less pressure there is.

Atmospheric pressure equal to the pressure of a column of mercury at a height of 760 mm Hg. Art. at a temperature of 0°C is called normal.

Normal atmospheric pressure is 101300 Pa = 1013 hPa. Figure 124 shows the change in atmospheric pressure with altitude. With small climbs, on average, for every 12 m of rise, the pressure decreases by 1 mmHg. Art. (or by 1.33 hPa).

Knowing the dependence of pressure on altitude, it is possible to determine the altitude above sea level by changes in barometer readings. Aneroids that have a scale on which the height of elevation can be directly measured are called altimeters. They are used in aviation and mountain climbing.

Questions. 1. How can we explain that atmospheric pressure decreases as the altitude above the Earth increases? 2. What atmospheric pressure is called normal? 3. What is the name of the device for measuring altitude using atmospheric pressure? What is he?

Exercises. 1. Explain why passengers experience ear pain when an airplane descends quickly. 2. How can we explain that when taking off on an airplane, ink begins to pour out of a charged automatic pen? 3. At the foot of the mountain the barometer shows 760 mm Hg. Art., and at the top - 722 mm Hg. Art. What is the height of the mountain? 4. Express normal atmospheric pressure in hectopascals (hPa).

Note. Pressure is measured using the formulap=pgh, where

g = 9.8 N/kg, h = 760 mm = 0.76 m, p = 13,600 kg/m3.

5. With a mass of 60 kg and a height of 1.6 m, the surface area of ​​the human body is approximately 1.6 m2. Calculate the force with which the atmosphere presses on a person. How can one explain that a person can withstand such great force and not feel its effect?

Exercise. Using an aneroid barometer, measure the atmospheric pressure on the first and last floors of the school building. Using the data obtained, determine the distance between floors. Verify these results by direct measurement.

How does the volume of air change when heated and cooled? How to prove that air has weight? Which air, warm or cold, is heavier?

1. The concept of atmospheric pressure and its measurement. The air is very light, but it exerts significant pressure on the earth's surface. The weight of air creates atmospheric pressure.

Air exerts pressure on all objects. To verify this, do the following experiment. Pour a full glass of water and cover it with a piece of paper. Press the paper against the edges of the glass with your palm and quickly turn it over. Remove your palm from the leaf and you will see that the water does not pour out of the glass because the air pressure presses the leaf to the edges of the glass and holds the water.

Atmosphere pressure- the force with which air presses on the earth's surface and on all objects located on it. For every square centimeter of the earth's surface, air exerts a pressure of 1.033 kilograms - i.e. 1.033 kg/cm2.

Barometers are used to measure atmospheric pressure. There are mercury barometers and metal ones. The latter is called an aneroid. In a mercury barometer (Fig. 17), a glass tube with mercury sealed at the top is lowered with its open end into a bowl of mercury; there is an airless space above the surface of the mercury in the tube. The change in atmospheric pressure on the surface of the mercury in the bowl causes the column of mercury to rise or fall. The amount of atmospheric pressure is determined by the height of the mercury column in the tube.

The main part of the aneroid barometer (Fig. 18) is a metal box, devoid of air and very sensitive to changes in atmospheric pressure. When the pressure decreases, the box expands, and when the pressure increases, it contracts. Changes in the box with the help of a simple device are transmitted to the arrow, which shows the atmospheric pressure on the scale. The scale is divided according to the mercury barometer.

If we imagine a column of air from the surface of the Earth to the upper layers of the atmosphere, then the weight of such an air column will be equal to the weight of a column of mercury 760 mm high. This pressure is called normal atmospheric pressure. This is the air pressure at parallel 45° at a temperature of 0°C at sea level. If the height of the column is more than 760 mm, then the pressure is increased, less - decreased. Atmospheric pressure is measured in millimeters of mercury (mmHg).

2. Change in atmospheric pressure. Atmospheric pressure changes continuously due to changes in air temperature and its movement. When air is heated, its volume increases, density and weight decrease. Because of this, atmospheric pressure decreases. The denser the air, the heavier it is, and the greater the atmospheric pressure. During the day it increases twice (morning and evening) and decreases twice (after noon and after midnight). Pressure increases where there is more air and decreases where air leaves. main reason movement of air - its heating and cooling from earth's surface. These fluctuations are especially well expressed in low latitudes. (What atmospheric pressure will be observed over land and over water at night?) During a year highest pressure V winter months, and the smallest in summer. (Explain this pressure distribution.) These changes are most pronounced in middle and high latitudes and weakest in low latitudes.

Atmospheric pressure decreases with altitude. Why is this happening? The change in pressure is caused by a decrease in the height of the air column that presses on the earth's surface. In addition, as altitude increases, air density decreases and pressure drops. At an altitude of about 5 km, atmospheric pressure decreases by half compared to normal pressure at sea level, at an altitude of 15 km - 8 times less, 20 km - 18 times.

Near the earth's surface it decreases by approximately 10 mm of mercury per 100 m of rise (Fig. 19).

At an altitude of 3000 m, a person begins to feel unwell and signs of altitude sickness appear: shortness of breath, dizziness. Above 4000 m the nose may bleed as small blood vessels, loss of consciousness is possible. This happens because with altitude the air becomes rarefied, and both the amount of oxygen in it and the atmospheric pressure decrease. The human body is not adapted to such conditions.

On the earth's surface, pressure is distributed unevenly. The air gets very hot near the equator (Why?), and the atmospheric pressure is low throughout the year. IN polar regions the air is cold and dense, the atmospheric pressure is high. (Why?)

? check yourself

Atmospheric pressure is considered normal within the range of 750-760 mm Hg. (millimeters of mercury). During the year it fluctuates within 30 mmHg. Art., and during the day - within 1-3 mm Hg. Art. A sharp change in atmospheric pressure often causes a deterioration in health in weather-sensitive people, and sometimes in healthy people.

If the weather changes, patients with hypertension also feel unwell. Let's consider how atmospheric pressure affects hypertensive and weather-sensitive people.

Weather dependent and healthy people

Healthy people do not feel any changes in the weather. People who are weather dependent experience the following symptoms:

• Dizziness;
• Drowsiness;
• Apathy, lethargy;
• Joint pain;
• Anxiety, fear;
• Gastrointestinal dysfunction;
• Fluctuations in blood pressure.

Often, health worsens in the fall, when there is an exacerbation of colds and chronic diseases. In the absence of any pathologies, meteosensitivity manifests itself as malaise.

Unlike healthy people, weather-dependent people react not only to fluctuations in atmospheric pressure, but also to increased humidity, sudden cold or warming. The reasons for this are often:

• Low physical activity;
• Presence of diseases;
• Decline of immunity;
• Deterioration of the central nervous system;
• Weak blood vessels;
• Age;
• Ecological situation;
• Climate.

As a result, the body's ability to quickly adapt to changes in weather conditions deteriorates.

High barometric pressure and hypertension

If the atmospheric pressure is high (above 760 mm Hg), there is no wind and precipitation, they speak of the onset of an anticyclone. There are no sudden temperature changes during this period. The amount of harmful impurities in the air increases.

Anticyclone has a negative effect on hypertensive patients. An increase in atmospheric pressure leads to an increase in blood pressure. Performance decreases, pulsation and pain in the head, and heart pain appear. Other symptoms negative influence anticyclone:

• Increased heart rate;
• Weakness;
• Noise in ears;
• Facial redness;
• Flashing "flies" before the eyes.

The number of white blood cells in the blood decreases, which increases the risk of developing infections.

Elderly people with chronic cardiovascular diseases are especially susceptible to the effects of the anticyclone.. With an increase in atmospheric pressure, the likelihood of a complication of hypertension - a crisis - increases, especially if the blood pressure rises to 220/120 mm Hg. Art. Other dangerous complications may develop (embolism, thrombosis, coma).

Low atmospheric pressure

Low atmospheric pressure also has a bad effect on patients with hypertension - a cyclone. It is characterized cloudy weather, precipitation, high humidity. Air pressure drops below 750 mm Hg. Art. The cyclone has the following effect on the body: breathing becomes more frequent, the pulse quickens, however, the force of the heart beat is reduced. Some people experience shortness of breath.

When air pressure is low, blood pressure also drops. Considering that hypertensive patients take medications to lower blood pressure, the cyclone has a bad effect on their well-being. The following symptoms appear:

• Dizziness;
• Drowsiness;
• Headache;
• Prostration.

In some cases, there is a deterioration in the functioning of the gastrointestinal tract.

With an increase in atmospheric pressure, patients with hypertension and weather dependent people Active physical activity should be avoided. We need to rest more. A low-calorie diet containing increased amounts of fruit is recommended.

Even “advanced” hypertension can be cured at home, without surgery or hospitals. Just remember once a day...

If the anticyclone is accompanied by heat, it is also necessary to exclude physical exercise. If possible, you should be in an air-conditioned room. A low-calorie diet will be relevant. Increase the amount of potassium-rich foods in your diet.