The atmospheric pressure is 740 mm Hg. What atmospheric pressure is normal

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Participant: Vertushkin Ivan Aleksandrovich
Head: Elena Anatolyevna Vinogradova

Subject: " Atmosphere pressure"

Introduction

It's raining outside the window today. After the rain, the air temperature decreased, humidity increased and atmospheric pressure decreased. Atmospheric pressure is one of the main factors determining the state of weather and climate, so knowledge of atmospheric pressure is necessary in weather forecasting. The ability to measure atmospheric pressure is of great practical importance. And it can be measured with special barometer devices. In liquid barometers, as the weather changes, the liquid column decreases or increases.

Knowledge of atmospheric pressure is necessary in medicine, in technological processes, human life and all living organisms. There is a direct connection between changes in atmospheric pressure and changes in weather. An increase or decrease in atmospheric pressure can be a sign of weather changes and affect a person’s well-being.

Description of three interrelated physical phenomena from Everyday life:

Relationship between weather and atmospheric pressure.
Phenomena underlying the operation of instruments for measuring atmospheric pressure.

Relevance of the work

The relevance of the chosen topic is that at all times people, thanks to their observations of animal behavior, could predict weather changes, natural disasters, avoid human casualties.

The influence of atmospheric pressure on our body is inevitable; sudden changes in atmospheric pressure affect a person’s well-being, and weather-dependent people especially suffer. Of course, we cannot reduce the influence of atmospheric pressure on human health, but we can help our own body. The ability to measure atmospheric pressure, knowledge of folk signs, use of homemade devices.

Goal of the work: find out what role atmospheric pressure plays in human daily life.

Tasks:

Study the history of atmospheric pressure measurement.
Determine whether there is a connection between weather and atmospheric pressure.
Study the types of instruments designed to measure atmospheric pressure, made by man.
Study the physical phenomena underlying the operation of instruments for measuring atmospheric pressure.
Dependence of liquid pressure on the height of the liquid column in liquid barometers.

Research methods

Literature analysis.
Summarizing the information received.
Observations.

Field of study: Atmosphere pressure

Hypothesis: atmospheric pressure has important for humans .

Significance of the work: the material of this work can be used in lessons and in extracurricular activities, in the lives of my classmates, students of our school, all lovers of nature research.

Work plan

I. Theoretical part (information collection):

Review and analysis of literature.
Internet resources.

II. Practical part:

observations;
collecting weather information.

III. Final part:

Conclusions.
Presentation of work.

History of atmospheric pressure measurement

We live at the bottom of a huge ocean of air called the atmosphere. All changes that occur in the atmosphere certainly have an impact on a person, on his health, lifestyle, because... man is an integral part of nature. Each of the factors that determine the weather: atmospheric pressure, temperature, humidity, ozone and oxygen content in the air, radioactivity, magnetic storms etc. has a direct or indirect effect on human well-being and health. Let's focus on atmospheric pressure.

Atmosphere pressure- this is the pressure of the atmosphere on all objects in it and the Earth's surface.

In 1640, the Grand Duke of Tuscany decided to build a fountain on the terrace of his palace and ordered water to be supplied from a nearby lake using a suction pump. The invited Florentine craftsmen said that this was impossible because the water had to be sucked up to a height of more than 32 feet (more than 10 meters). They could not explain why the water is not absorbed to such a height. The Duke asked the great Italian scientist Galileo Galilei to figure it out. Although the scientist was already old and sick and could not engage in experiments, he nevertheless suggested that the solution to the problem lay in the area of determining the weight of air and its pressure on the water surface of the lake. Galileo's student Evangelista Torricelli took up the task of resolving this issue. To test his teacher's hypothesis, he conducted his famous experiment. A glass tube 1 m long, sealed at one end, was completely filled with mercury, and tightly closing the open end of the tube, turned it over with this end into a cup with mercury. Some of the mercury poured out of the tube, some remained. An airless space formed above the mercury. The atmosphere presses on the mercury in the cup, the mercury in the tube also presses on the mercury in the cup, since equilibrium has been established, these pressures are equal. To calculate the pressure of mercury in a tube means to calculate the pressure of the atmosphere. If atmospheric pressure increases or decreases, the column of mercury in the tube increases or decreases accordingly. This is how the unit of measurement of atmospheric pressure appeared - mm. rt. Art. – millimeter of mercury. While observing the level of mercury in the tube, Torricelli noticed that the level was changing, which meant that it was not constant and depended on changes in the weather. If the pressure rises, the weather will be good: cold in winter, hot in summer. If the pressure drops sharply, it means that cloudiness and saturation of air with moisture are expected. A Torricelli tube with a ruler attached represents the first instrument for measuring atmospheric pressure - a mercury barometer. (Annex 1)

Other scientists also created barometers: Robert Hooke, Robert Boyle, Emil Marriott. Water barometers were designed by the French scientist Blaise Pascal and the German burgomaster of the city of Magdeburg, Otto von Guericke. The height of such a barometer was more than 10 meters.

To measure pressure, different units are used: mm of mercury, physical atmospheres, and in the SI system - Pascals.

Relationship between weather and atmospheric pressure

In Jules Verne's novel “The Fifteen-Year-Old Captain,” I was interested in the description of how to understand barometer readings.

“Captain Gul, a good meteorologist, taught him to understand the barometer readings. We will briefly tell you how to use this wonderful device.

When, after a long period of good weather, the barometer begins to fall sharply and continuously, this is a sure sign of rain. However, if good weather stood for a very long time, the mercury column can drop for two or three days, and only after that any noticeable changes will occur in the atmosphere. In such cases, the more time passes between the start of the mercury fall and the start of rains, the longer the rainy weather will persist.

On the contrary, if during a long period of rain the barometer begins to rise slowly but continuously, the onset of good weather can be confidently predicted. And good weather will remain the longer, the more time has passed between the beginning of the mercury rise and the first clear day.

In both cases, a change in weather that occurs immediately after the rise or fall of the mercury column persists for a very short time.

If the barometer rises slowly but continuously for two or three days or longer, this portends good weather, even if it has been raining non-stop all these days, and vice versa. But if the barometer rises slowly on rainy days, and immediately begins to fall when good weather comes, the good weather will not last long, and vice versa

In spring and autumn, a sharp drop in the barometer foreshadows windy weather. In summer, in extreme heat, it predicts a thunderstorm. In winter, especially after prolonged frosts, a rapid drop in the mercury column indicates an upcoming change in wind direction, accompanied by thaw and rain. On the contrary, an increase in mercury during prolonged frosts foretells snowfall.

Frequent fluctuations in the level of the mercury column, sometimes rising, sometimes falling, should in no case be considered as a sign of the approach of a long period; periods of dry or rainy weather. Only a gradual and slow fall or rise in the mercury heralds the onset of a long period of stable weather.

When, at the end of autumn, after a long period of wind and rain, the barometer begins to rise, this heralds a north wind at the onset of frost.

Here are the general conclusions that can be drawn from the readings of this valuable device. Dick Sand was an excellent judge of the barometer's predictions and was convinced many times how correct they were. Every day he consulted his barometer so as not to be taken by surprise by changes in the weather.”

I made observations of weather changes and atmospheric pressure. And I became convinced that this dependence exists.

date	Temperature,°C	Precipitation,	Atmospheric pressure, mm Hg.	Cloudiness

				Mainly cloudy

				Mainly cloudy
				Mainly cloudy
				Mainly cloudy
				Mainly cloudy




				Mainly cloudy

				Mainly cloudy

Instruments for measuring atmospheric pressure

For scientific and everyday purposes, you need to be able to measure atmospheric pressure. There are special devices for this - barometers. Normal atmospheric pressure is the pressure at sea level at a temperature of 15 °C. It is equal to 760 mm Hg. Art. We know that when the altitude changes by 12 meters, the atmospheric pressure changes by 1 mmHg. Art. Moreover, with increasing altitude, atmospheric pressure decreases, and with decreasing altitude, it increases.

The modern barometer is made liquidless. It's called an aneroid barometer. Metal barometers are less accurate, but not as bulky or fragile.

- a very sensitive device. For example, when climbing to the top floor of a nine-story building, due to differences in atmospheric pressure at different altitudes, we will find a decrease in atmospheric pressure by 2-3 mmHg. Art.

A barometer can be used to determine the flight altitude of an aircraft. This barometer is called a barometric altimeter or altimeter. The idea of Pascal's experiment formed the basis for the design of the altimeter. It determines the altitude above sea level by changes in atmospheric pressure.

When observing the weather in meteorology, if it is necessary to record fluctuations in atmospheric pressure over a certain period of time, they use a recorder - barograph.

(Storm Glass) (stormglass, Dutch. storm- "storm" and glass- “glass”) is a chemical or crystalline barometer consisting of a glass flask or ampoule filled with an alcohol solution in which camphor, ammonia and potassium nitrate are dissolved in certain proportions.

I actively used this chemical barometer during my sea travel English hydrographer and meteorologist, Vice Admiral Robert Fitzroy, who carefully described the behavior of the barometer, a description that is still used today. Therefore, stormglass is also called the "Fitzroy Barometer". From 1831–36, Fitzroy led the oceanographic expedition on HMS Beagle, which included Charles Darwin.

The barometer works as follows. The flask is hermetically sealed, but, nevertheless, the birth and disappearance of crystals constantly occurs in it. Depending on upcoming weather changes, crystals form in the liquid various shapes. Stormglass is so sensitive that it can predict sudden weather changes 10 minutes in advance. The principle of operation has never received a complete scientific explanation. The barometer works better when located near a window, especially in reinforced concrete houses; probably in this case the barometer is not so shielded.

Baroscope– a device for monitoring changes in atmospheric pressure. You can make a baroscope with your own hands. To make a baroscope, the following equipment is required: A glass jar with a volume of 0.5 liters.

A piece of film from a balloon.
Rubber ring.
Lightweight straw arrow.
Wire for fastening the arrow.
Vertical scale.
Device body.

Dependence of liquid pressure on the height of the liquid column in liquid barometers

When atmospheric pressure changes in liquid barometers, the height of the liquid column (water or mercury) changes: when the pressure decreases, it decreases, when the pressure increases, it increases. This means that there is a dependence of the height of the liquid column on atmospheric pressure. But the liquid itself presses on the bottom and walls of the vessel.

The French scientist B. Pascal in the middle of the 17th century empirically established a law called Pascal's law:

Pressure in a liquid or gas is transmitted equally in all directions and does not depend on the orientation of the area on which it acts.

To illustrate Pascal's law, the figure shows a small rectangular prism immersed in a liquid. If we assume that the density of the prism material is equal to the density of the liquid, then the prism must be in a state of indifferent equilibrium in the liquid. This means that the pressure forces acting on the edge of the prism must be balanced. This will only happen if the pressures, i.e. the forces acting per unit surface area of each face, are the same: p 1 = p 2 = p 3 = p.

The pressure of the liquid on the bottom or side walls of the vessel depends on the height of the liquid column. Pressure force on the bottom of a cylindrical vessel of height h and base area S equal to the weight of a column of liquid mg, Where m = ρ ghS is the mass of the liquid in the vessel, ρ is the density of the liquid. Therefore p = ρ ghS / S

Same pressure at depth h in accordance with Pascal's law, the liquid also affects the side walls of the vessel. Liquid column pressure ρ gh called hydrostatic pressure.

Many devices that we encounter in life use the laws of liquid and gas pressure: communicating vessels, water supply, hydraulic press, sluices, fountains, artesian well, etc.

Conclusion

Atmospheric pressure is measured in order to more likely predict possible weather changes. There is a direct connection between pressure changes and weather changes. An increase or decrease in atmospheric pressure with some probability can serve as a sign of weather changes. You need to know: if the pressure drops, then cloudy, rainy weather is expected, but if it rises, dry weather is expected, with cold weather in winter. If the pressure drops very sharply, serious bad weather is possible: a storm, severe thunderstorm or storm.

Even in ancient times, doctors wrote about the influence of weather on the human body. In Tibetan medicine there is a mention: “joint pain increases in rainy times and during periods of high winds.” The famous alchemist and physician Paracelsus noted: “He who has studied the winds, lightning and weather knows the origin of diseases.”

In order for a person to be comfortable, the atmospheric pressure must be equal to 760 mm. rt. Art. If the atmospheric pressure deviates even by 10 mm in one direction or another, a person feels uncomfortable and this can affect his health. Adverse phenomena are observed during the period of changes in atmospheric pressure - increase (compression) and especially its decrease (decompression) to normal. The slower the change in pressure occurs, the better and without adverse consequences the human body adapts to it.

The air surrounding the Earth has mass, and despite the fact that the mass of the atmosphere is approximately a million times less than the mass of the Earth (the total mass of the atmosphere is 5.2 * 10 21 g, and 1 m 3 of air has earth's surface weighs 1.033 kg), this mass of air exerts pressure on all objects located on the earth's surface. The force with which air presses on the earth's surface is called atmospheric pressure.

A column of air weighing 15 tons presses on each of us. Such pressure can crush all living things. Why don't we feel it? This is explained by the fact that the pressure inside our body is equal to atmospheric pressure.

In this way, internal and external pressures are balanced.

Barometer

Atmospheric pressure is measured in millimeters of mercury (mmHg). To determine it, they use a special device - a barometer (from the Greek baros - heaviness, weight and metreo - I measure). There are mercury and liquid-free barometers.

Liquidless barometers are called aneroid barometers(from the Greek a - negative particle, nerys - water, i.e. acting without the help of liquid) (Fig. 1).

Rice. 1. Aneroid barometer: 1 - metal box; 2 - spring; 3 - transmission mechanism; 4 — pointer arrow; 5 - scale

Normal atmospheric pressure

Normal atmospheric pressure is conventionally taken to be air pressure at sea level at a latitude of 45° and at a temperature of 0 °C. In this case, the atmosphere presses on every 1 cm 2 of the earth's surface with a force of 1.033 kg, and the mass of this air is balanced by a mercury column 760 mm high.

Torricelli experience

The value of 760 mm was first obtained in 1644. Evangelista Torricelli(1608-1647) and Vincenzo Viviani(1622-1703) - students of the brilliant Italian scientist Galileo Galilei.

E. Torricelli sealed a long glass tube with divisions at one end, filled it with mercury and lowered it into a cup of mercury (this is how the first mercury barometer was invented, which was called the Torricelli tube). The mercury level in the tube dropped as some of the mercury spilled into the cup and settled at 760 millimeters. A void formed above the column of mercury, which was called Torricelli's void(Fig. 2).

E. Torricelli believed that the atmospheric pressure on the surface of the mercury in the cup is balanced by the weight of the mercury column in the tube. The height of this column above sea level is 760 mm Hg. Art.

Rice. 2. Torricelli experience

1 Pa = 10 -5 bar; 1 bar = 0.98 atm.

High and low atmospheric pressure

Air pressure on our planet can vary widely. If the air pressure is more than 760 mm Hg. Art., then it is considered elevated, less - reduced.

Since the air becomes more and more rarefied as it rises upward, the atmospheric pressure decreases (in the troposphere on average 1 mm for every 10.5 m of rise). Therefore, for territories located at different altitudes above sea level, the average value of atmospheric pressure will be different. For example, Moscow lies at an altitude of 120 m above sea level, so its average atmospheric pressure is 748 mm Hg. Art.

Atmospheric pressure rises twice during the day (morning and evening) and decreases twice (after noon and after midnight). These changes are due to the change and movement of air. During the year on the continents, the maximum pressure is observed in winter, when the air is supercooled and compacted, and the minimum pressure is observed in summer.

The distribution of atmospheric pressure over the earth's surface has a pronounced zonal character. This is due to uneven heating of the earth's surface, and consequently, changes in pressure.

On globe Three belts with a predominance of low atmospheric pressure (minima) and four zones with a predominance of high atmospheric pressure (maxima) are distinguished.

At equatorial latitudes, the Earth's surface warms up greatly. Heated air expands, becomes lighter and therefore rises. As a result, low atmospheric pressure is established near the earth's surface near the equator.

At the poles, under the influence of low temperatures, the air becomes heavier and sinks. Therefore, at the poles the atmospheric pressure is increased by 60-65° compared to the latitudes.

In the high layers of the atmosphere, on the contrary, over hot areas the pressure is high (although lower than at the Earth's surface), and over cold areas it is low.

The general diagram of the distribution of atmospheric pressure is as follows (Fig. 3): along the equator there is a belt low pressure; at 30-40° latitude of both hemispheres - high pressure belts; 60-70° latitude - low pressure zones; in the polar regions there are areas of high pressure.

As a result of the fact that in temperate latitudes Northern Hemisphere In winter, atmospheric pressure over the continents increases greatly, and the low pressure belt is interrupted. It persists only over oceans as closed areas low blood pressure— Icelandic and Aleutian minimums. On the contrary, winter maximums form over the continents: Asian and North American.

Rice. 3. General diagram of atmospheric pressure distribution

In summer, in the temperate latitudes of the Northern Hemisphere, the belt of low atmospheric pressure is restored. A huge area of low atmospheric pressure centered in tropical latitudes—the Asian Low—forms over Asia.

In tropical latitudes, the continents are always warmer than the oceans, and the pressure above them is lower. Thus, there are maxima over the oceans throughout the year: North Atlantic (Azores), North Pacific, South Atlantic, South Pacific and South Indian.

Lines that are on climate map connect points with the same atmospheric pressure are called isobars(from the Greek isos - equal and baros - heaviness, weight).

The closer the isobars are to each other, the faster the atmospheric pressure changes over a distance. The amount of change in atmospheric pressure per unit distance (100 km) is called pressure gradient.

The formation of atmospheric pressure belts near the earth's surface is influenced by the uneven distribution of solar heat and the rotation of the Earth. Depending on the time of year, both hemispheres of the Earth are heated by the Sun differently. This causes some movement of the atmospheric pressure belts: in summer - to the north, in winter - to the south.

We are taught about what atmospheric pressure is at school during natural history and geography lessons. We get acquainted with this information and safely throw it out of our heads, rightly believing that we will never be able to use it.

But years later, stress and environmental conditions environment will have a sufficient impact on us. And the concept of “geodependence” will no longer seem nonsense, since pressure surges and headache will begin to poison life. At this moment you will have to remember what it is like in Moscow, for example, in order to adapt to new conditions. And move on with your life.

School basics

The atmosphere that surrounds our planet, unfortunately, literally puts pressure on all living and nonliving things. There is a term to define this phenomenon - atmospheric pressure. This is the force of the air column acting on the area. In the SI system we talk about kilograms per square centimeter. Normal atmospheric pressure (optimal indicators for Moscow have long been known) affects the human body with the same force as a weight weighing 1.033 kg. But most of us don't notice this. There are enough gases dissolved in body fluids to neutralize all unpleasant sensations.

Atmospheric pressure standards vary in different regions. But 760 mmHg is considered ideal. Art. Experiments with mercury turned out to be the most revealing at a time when scientists were proving that air has weight. Mercury barometers are the most common devices for determining pressure. It should also be remembered that the ideal conditions for which the mentioned 760 mm Hg are relevant. Art., is a temperature of 0 ° C and the 45th parallel.

IN international system units are used to define pressure in Pascals. But for us, the use of mercury column fluctuations is more familiar and understandable.

Relief features

Of course, many factors influence the value of atmospheric pressure. The most significant are the relief and proximity to magnetic poles planets. The norm of atmospheric pressure in Moscow is fundamentally different from the indicators in St. Petersburg; and for residents of some remote village in the mountains, this figure may seem completely abnormal. Already at 1 km above sea level it corresponds to 734 mm Hg. Art.

As already noted, in the region of the Earth’s poles the amplitude of pressure changes is much higher than in equatorial zone. Even during the day, the atmospheric pressure changes slightly. Insignificantly, however, only by 1-2 mm. This is due to the difference between day and night temperatures. At night it is usually cooler, which means the pressure is higher.

Pressure and man

For a person, in essence, it does not matter what atmospheric pressure is: normal, low or high. These are very conditional definitions. People tend to get used to everything and adapt. The dynamics and magnitude of changes in atmospheric pressure are much more important. On the territory of the CIS countries, in particular in Russia, there are quite a lot of zones. Often, local residents do not even know about it.

The norm of atmospheric pressure in Moscow, for example, may well be considered as a variable value. After all, every skyscraper is a kind of mountain, and the higher and faster you go up (or go down), the more noticeable the difference will be. Some people may well pass out while riding a high-speed elevator.

Adaptation

Doctors almost unanimously agree that the question “what atmospheric pressure is considered normal” (Moscow or any populated area on the planet is not important) is incorrect in itself. Our body adapts perfectly to life above or below sea level. And if the pressure does not have a detrimental effect on a person, it can be considered normal for the area. Doctors say that the normal atmospheric pressure in Moscow and other large cities is in the range from 750 to 765 mm Hg. pillar

The pressure drop is a completely different matter. If within a few hours it rises (falls) by 5-6 mm, people begin to experience discomfort and pain. This is especially dangerous for the heart. Its beating becomes more frequent, and a change in the frequency of breaths leads to a change in the rhythm of oxygen supply to the body. The most common ailments in such a situation are weakness, etc.

Meteor dependence

Normal atmospheric pressure for Moscow may seem like a nightmare to a visitor from the North or the Urals. After all, each region has its own norm and, accordingly, its own understanding of the stable state of the body. And since in life we do not concentrate on exact pressure indicators, weather forecasters always focus on whether the pressure is high or low for a given region.

After all, not every person can boast that they do not notice the corresponding changes. Anyone who cannot call himself lucky in this matter must systematize his feelings during pressure changes and find acceptable countermeasures. Often a cup of strong coffee or tea is enough, but sometimes more serious help in the form of medication is needed.

Pressure in the metropolis

Residents of megacities are the most weather-dependent. It is here that a person experiences more stress, lives life at a high pace and experiences environmental degradation. Therefore, knowing what the normal atmospheric pressure is for Moscow is vital.

The capital of the Russian Federation is located on the Central Russian Upland, which means that there is a priori a zone of low pressure. Why? It's very simple: the higher you are above sea level, the lower the atmospheric pressure. For example, on the banks of the Moscow River this figure will be 168 m. And the maximum value in the city was recorded in Teply Stan - 255 m above sea level.

It is quite possible to assume that Muscovites will experience abnormally low atmospheric pressure much less frequently than residents of other regions, which, of course, cannot but make them happy. And yet, what atmospheric pressure is considered normal in Moscow? Meteorologists say that it usually does not exceed 748 mm Hg. pillar This means little, since we already know that even a quick ride in an elevator can have a significant impact on a person's heart.

On the other hand, Muscovites do not feel any discomfort if the pressure fluctuates between 745-755 mm Hg. Art.

Danger

But from the point of view of doctors, not everything is so optimistic for the residents of the metropolis. Many experts quite reasonably believe that by working on the upper floors of business centers, people expose themselves to danger. Indeed, in addition to the fact that they live in a zone of low pressure, they also spend almost a third of the day in places with

If we add to this fact violations of the building ventilation system and permanent job air conditioners, it becomes obvious that the employees of such offices are the most incapacitated, sleepy and sick.

Results

Actually, there are a few things to remember. Firstly, there is no single ideal value for normal atmospheric pressure. There are regional standards that can vary significantly in absolute terms. Secondly, features human body make it easy to experience pressure changes if they happen rather slowly. Thirdly, the more healthy image life we lead and the more often we manage to maintain a daily routine (getting up at the same time, long night sleep, following a basic diet, etc.), the less we are susceptible to weather dependence. This means they are more energetic and cheerful.

Everyone knows that the formula for calculating liquid pressure is as follows: p = ρgh, where p is the pressure of the liquid at the bottom of the vessel, ρ is the density of water, g is the force of gravity acting on 1 kg, h is the height of the liquid column.

But to calculate atmospheric pressure using this formula, we need to know the height of the atmosphere and the density of the air. Since the atmosphere does not have a definite boundary, calculating atmospheric pressure using this formula is impossible.

How to measure atmospheric pressure? Toricelli's experience

But how can we measure it then? An Italian scientist who studied with Galileo, Evangelista Torricelli, helped us with this. He conducted an experiment where he took a glass tube, sealed at one end, about 1 m long, and filled it with mercury. The other end of the tube was plugged.

The tube was lowered with its plugged end into the bowl and it was opened, as a result of which some of the mercury poured into the bowl. The height of the mercury column was approximately 760 mm. There is an airless space between the top of the mercury column and the end of the tube.

But it would seem What does atmospheric pressure have to do with it? But here’s the thing: the atmosphere presses on the surface of the mercury, while the mercury is in equilibrium. It follows from this that the pressure of mercury in the tube at the level of the surface of the mercury in the bowl is equal to atmospheric pressure.

If there is more of it, then the mercury will pour out of the tube; if it is less, then the mercury from the bowl will flow into the tube. from this experiment it follows that atmospheric pressure is equal to the pressure of mercury in the tube (p atm = p mercury).

Now, having measured the height of the mercury column, we can calculate the atmospheric pressure, which will be equal to: the density of mercury multiplied by the force of gravity acting by 1 kg times the height of the mercury column. This will be the atmospheric pressure.

Atmospheric pressure in millimeters of mercury

Since in Torricelli's experiment the higher the atmospheric pressure, the higher the column of mercury in the tube, it became customary to measure atmospheric pressure in millimeters of mercury (mmHg). If the pressure is 760 mm Hg. Art., then the height of the mercury column in the tube will be equal to 760 mm, respectively.

Let's draw a parallel with the unit of pressure we know - pascal (Pa). So, the pressure is 1 mmHg. Art. equals...

p = gρh, p = 9.8 N/kg * 13600 kg/m^3 * 0.001m ≈ 133.3 Pa.

Equals 133.3 Pa, where 9.8 N/kg is the force of gravity acting on 1 kg 13600 kg/m^3 is the density (ρ) of mercury, and 0.001 m is 1 millimeter of mercury.

In weather reports you can hear that the atmospheric pressure is 1030 hectopascals (1030 hPa). This is the same as 760 mmHg. Art. and is normal atmospheric pressure.

It is no secret that atmospheric pressure is unstable and changes throughout the day. Often this occurs due to weather changes.

Nowadays no one measures the height of the mercury column in a tube with a ruler. To measure atmospheric pressure, a mercury barometer is used (from the Greek baros - heaviness and metro - to measure). The simplest mercury barometer can be obtained by attaching a vertical measuring scale to a tube containing mercury, which was used in Torricelli’s experiment.

For normal atmospheric pressure, it is customary to take the air pressure at sea level at a latitude of 45 degrees at a temperature of 0°C. Under these ideal conditions, the column of air presses on each area with the same force as a column of mercury 760 mm high. This figure is an indicator of normal atmospheric pressure.

Atmospheric pressure depends on the altitude of the area above sea level. At higher elevations, the indicators may differ from ideal, but they will also be considered the norm.

Atmospheric pressure standards in different regions

As altitude increases, atmospheric pressure decreases. So, at an altitude of five kilometers, pressure indicators will be approximately two times less than below.

Due to the location of Moscow on a hill, the normal pressure level here is considered to be 747-748 mm column. In St. Petersburg, normal pressure is 753-755 mm Hg. This difference is explained by the fact that the city on the Neva is located lower than Moscow. In some areas of St. Petersburg you can find a pressure norm of an ideal 760 mm Hg. For Vladivostok, normal pressure is 761 mmHg. And in the mountains of Tibet – 413 mmHg.

Impact of atmospheric pressure on people

A person gets used to everything. Even if normal pressure readings are low compared to the ideal 760 mmHg, but are the norm for the area, people will.

A person’s well-being is affected by sharp fluctuations in atmospheric pressure, i.e. decrease or increase in pressure by at least 1 mmHg within three hours

When pressure decreases, a lack of oxygen occurs in a person’s blood, hypoxia of body cells develops, and the heartbeat increases. Headaches appear. There are difficulties from respiratory system. Due to poor blood supply, a person may experience pain in the joints and numbness in the fingers.

Increased pressure leads to an excess of oxygen in the blood and tissues of the body. The tone of blood vessels increases, which leads to their spasms. As a result, the body's blood circulation is disrupted. Visual disturbances may occur in the form of spots before the eyes, dizziness, and nausea. A sharp increase in pressure to large values can lead to rupture of the eardrum.