Definition of pressure as a physical quantity. Pressure formula for air, vapor, liquid or solid

Pressure This term has other meanings, see Pressure (meanings). Dimension Units SI CGS

Pressure- a physical quantity numerically equal to the force F acting per unit surface area S perpendicular to this surface. At a given point, pressure is defined as the ratio of the normal component of the force acting on a small surface element to its area:

The average pressure over the entire surface is the ratio of the force to the surface area:

Pressure characterizes the state of a continuous medium and is the diagonal component of the stress tensor. In the simplest case of an isotropic equilibrium stationary medium, the pressure does not depend on the orientation. Pressure can also be considered a measure of the potential energy stored in a continuous medium per unit volume and measured in units of energy per unit volume.

Pressure is an intensive physical quantity. Pressure in the SI system is measured in pascals (newtons per square meter, or, equivalently, joules per cubic meter); The following units are also used:

Technical atmosphere (ata - absolute, ati - excess)
physical atmosphere
millimeter of mercury
Water column meter
inch of mercury
Pound-force per square inch

Pressure units Pascal
(Pa, Pa) Bar

(mmHg,mmHg, Torr, Torr) Water column meter
(m water column, m H 2 O) Pound-force
per sq. inch
(psi) 1 Pa 1 bar 1 atm 1 atm 1 mmHg 1 m water Art. 1psi

Measurement of the pressure of gases and liquids is carried out using pressure gauges, differential pressure gauges, vacuum gauges, pressure sensors, atmospheric pressure- barometers, blood pressure - tonometers.

Notes

English E.R. Cohen et al., "Quantities, Units and Symbols in Physical Chemistry", IUPAC Green Book, 3rd Edition, 2nd Printing, IUPAC & RSC Publishing, Cambridge (2008). - p. fourteen.

Hi all!

Weather Seasons Precipitation Forecast and Clouds Humidity (absolute and relative) Pressure Air temperature Wind direction Wind Thunderstorm Tornado Hurricane Storm Categories:

Physical quantities alphabetically
Pressure units

Pressure units

Pascal (newton per square meter)
Millimeter of mercury (torr)
Micron of mercury (10−3 Torr)
Millimeter of water (or water) column
Atmosphere
- physical atmosphere
- Atmosphere technical
Kilogram-force square centimeter, kilogram-force per square meter
Dyne per square centimeter (barium)
Pound-force per square inch (psi)
Pieza (ton-force per square meter, walls per square meter)

Pressure units Pascal
(Pa, Pa) Bar
(bar) Technical atmosphere
(at, at) Physical atmosphere
(atm, atm) Millimeter of mercury
(mm Hg, mm Hg, Torr, Torr) Water column meter
(m water column, m H 2 O) Pound-force
per sq. inch
(psi) 1 Pa 1 bar 1 atm 1 atm 1 mmHg Art. 1 m water Art. 1psi

Blood pressure - what is it? What blood pressure is considered normal

What does blood pressure mean? Everything is quite simple. It is one of the main indicators of the activity of the cardiovascular system. Let's look at this issue in more detail.

What is BP?

Blood pressure is the process of squeezing the walls of capillaries, arteries and veins under the influence of blood circulation.

Types of blood pressure:

upper, or systolic;
lower, or diastolic.

When determining the level of blood pressure, both of these values \u200b\u200bmust be taken into account. The units of its measurement remained the very first - millimeters of a mercury column. This is due to the fact that mercury was used in the old devices to determine the level of blood pressure. Therefore, the BP indicator looks like this: upper blood pressure (for example, 130) / lower blood pressure (for example, 70) mm Hg. Art.

Circumstances that directly affect the range of blood pressure include:

the level of strength of contractions performed by the heart;
the proportion of blood pushed out by the heart during each contraction;
wall resistance blood vessels which turns out to be a blood stream;
the amount of blood circulating in the body;
pressure fluctuations in chest that are caused by the respiratory process.

Blood pressure levels can change throughout the day and with age. But for most healthy people characterized by stable blood pressure.

Definition of types of blood pressure

Systolic (upper) blood pressure is a characteristic of the general condition of the veins, capillaries, arteries, as well as their tone, which is caused by contraction of the heart muscle. It is responsible for the work of the heart, namely, with what force the latter is able to expel blood.

Thus, the level of upper pressure depends on the strength and speed with which heart contractions occur.

It is unreasonable to assert that arterial and cardiac pressure is the same concept, since the aorta also participates in its formation.

Lower (diastolic) pressure characterizes the activity of blood vessels. In other words, this is the level of blood pressure at the moment when the heart is maximally relaxed.

Lower pressure is formed as a result of contraction peripheral arteries, through which blood enters the organs and tissues of the body. Therefore, the state of blood vessels is responsible for the level of blood pressure - their tone and elasticity.

How to know the level of blood pressure?

You can find out your blood pressure level using a special device called a blood pressure monitor. This can be done both at the doctor's (or nurse's) and at home, having previously bought the device at the pharmacy.

There are the following types of tonometers:

automatic;
semi-automatic;
mechanical.

A mechanical tonometer consists of a cuff, a pressure gauge or display, a pear for pumping air and a stethoscope. Principle of operation: put the cuff on your arm, put a stethoscope under it (while you should hear the pulse), inflate the cuff with air until it stops, and then start to lower it gradually, unscrewing the wheel on the pear. At some point, you will clearly hear pulsating sounds in the stethoscope headphones, then they will stop. These two marks are the upper and lower blood pressure.

The semi-automatic tonometer consists of a cuff, an electronic display and a pear. Principle of operation: put on the cuff, pump up the air to the maximum with a pear, then let it out. The electronic display shows the upper and lower values of blood pressure and the number of beats per minute - the pulse.

The automatic blood pressure monitor consists of a cuff, an electronic display and a compressor that performs inflation and deflation manipulations. Principle of operation: put on the cuff, start the device and wait for the result.

It is generally accepted that a mechanical tonometer gives the most accurate result. It's also more affordable. At the same time, automatic and semi-automatic blood pressure monitors remain the most convenient to use. Such models are especially suitable for older people. Moreover, some types have the function of voice notification of pressure indicators.

It is worth measuring blood pressure indicators no earlier than thirty minutes after any physical exertion (even minor ones) and an hour after drinking coffee and alcohol. Before the measurement process itself, you need to sit quietly for a couple of minutes, catch your breath.

Blood pressure - the norm by age

Each person has an individual norm of blood pressure, which may not be associated with any diseases.

The level of blood pressure is determined by a number of factors that are of particular importance:

age and gender of the person;
personal characteristics;
life style;
lifestyle features labor activity, preferred type of vacation, and so on).

Blood pressure also tends to rise with unusual physical activity and emotional stress. And if a person constantly performs physical activity (for example, an athlete), then the level of blood pressure can also change both for a while and for a long period. For example, when a person in stressful condition, then his blood pressure can rise to thirty mm Hg. Art. from the norm.

However, there are still certain limits of normal blood pressure. And even every ten points of deviation from the norm indicate a violation of the body.

Blood pressure - the norm by age

You can also calculate the individual value of blood pressure using the following formulas:

1. For men:

upper BP \u003d 109 + (0.5 * number of full years) + (0.1 * weight in kg);
lower BP \u003d 74 + (0.1 * number of full years) + (0.15 * weight in kg).

2. For women:

upper BP \u003d 102 + (0.7 * number of full years) + 0.15 * weight in kg);
lower blood pressure \u003d 74 + (0.2 * number of full years) + (0.1 * weight in kg).

The resulting value is rounded to an integer according to the rules of arithmetic. That is, if it turned out to be 120.5, then when rounded it will be 121.

Elevated blood pressure

High blood pressure is a high level of at least one of the indicators (lower or upper). It is necessary to judge the degree of its overestimation, taking into account both indicators.

Regardless of whether the lower blood pressure is high or upper, it is a disease. And it's called hypertension.

There are three degrees of the disease:

the first - SAD 140-160 / DBP 90-100;
the second - SAD 161-180 / DBP 101-110;
the third - GARDEN 181 and more / DBP 111 and more.

It is worth talking about hypertension when there is a high level of blood pressure values for a long period.

According to statistics, an overestimated indicator of systolic pressure is most often observed in women, and diastolic - in men and the elderly.

Symptoms of high blood pressure can be:

decrease in working capacity;
appearance of fatigue;
frequent feelings of weakness;
morning pain in the back of the head;
frequent dizziness;
occurrence of bleeding from the nose;
noise in ears;
decreased visual acuity;
the appearance of swelling of the legs at the end of the day.

Causes of high blood pressure

If the lower blood pressure is high, then most likely this is one of the symptoms of a disease of the thyroid gland, kidneys, adrenal glands, which began to produce renin in large quantities. It, in turn, increases the tone of the muscles of the blood vessels.

Elevated lower blood pressure is fraught with the development of more more serious illnesses.

High upper pressure indicates too frequent contractions of the heart.

A jump in blood pressure can be caused by a number of reasons. This is for example:

vasoconstriction due to atherosclerosis;
overweight;
diabetes;
stressful situations;
malnutrition;
excessive consumption of alcohol, strong coffee and tea;
smoking;
lack of physical activity;
frequent weather changes;
some diseases.

What is low BP?

Low blood pressure is vegetovascular dystonia or hypotension.

What happens with hypotension? When the heart contracts, blood enters the vessels. They expand and then gradually narrow. Thus, the vessels help the blood to move further through the circulatory system. The pressure is normal. For a number of reasons, vascular tone may decrease. They will remain expanded. Then there is not enough resistance for the movement of blood, because of which the pressure drops.

The level of blood pressure in hypotension: upper - 100 or less, lower - 60 or less.

If the pressure drops sharply, then the blood supply to the brain is limited. And this is fraught with such consequences as dizziness and fainting.

Symptoms of low blood pressure may include:

increased fatigue and lethargy;
darkening in the eyes;
frequent shortness of breath;
cold feeling in hands and feet;
hypersensitivity to loud sounds and bright light
muscle weakness;
motion sickness in transport;
frequent headaches.

What is the reason for low blood pressure?

Poor joint tone and low blood pressure (hypotension) can be present from birth. But more often the culprits reduced pressure become:

Severe fatigue and stress. Congestion at work and at home, stress and lack of sleep cause a decrease in vascular tone.
Heat and stuffiness. When you sweat, it leaves the body a large number of liquids. In order to maintain water balance, it pumps water out of the blood that flows through the veins and arteries. Its volume decreases, vascular tone decreases. The pressure drops.
Taking medication. Heart drugs, antibiotics, antispasmodics and painkillers can “drop” the pressure.
emergence allergic reactions anything with possible anaphylactic shock.

If you have not had hypotension before, do not leave unpleasant symptoms without attention. They can be dangerous "bells" of tuberculosis, stomach ulcers, complications after a concussion and other diseases. Contact a therapist.

What to do to normalize the pressure?

These tips will help you feel whole hearty day if you are hypotensive.

Don't rush to get out of bed. Wake up - do a little warm-up lying down. Move your arms and legs. Then sit down and stand up slowly. Perform actions without sudden movements. they can cause fainting.
Take a contrast shower in the morning for 5 minutes. Alternate water - a minute warm, a minute cool. This will help to cheer up and is good for blood vessels.
A good cup of coffee! But only natural tart drink will raise the pressure. Drink no more than 1-2 cups per day. If you have heart problems, drink green tea instead of coffee. It invigorates no worse than coffee, but does not harm the heart.
Sign up for a pool. Go at least once a week. Swimming improves vascular tone.
Buy a tincture of ginseng. This natural "energy" gives tone to the body. Dissolve 20 drops of tincture in ¼ cup of water. Drink half an hour before meals.
Eat sweets. As soon as you feel weak - eat ½ teaspoon of honey or a little dark chocolate. Sweets will drive away fatigue and drowsiness.
Drink clean water. Daily 2 liters of pure and non-carbonated. This will help maintain pressure on normal level. If you have diseased heart and kidneys, the drinking regimen should be prescribed by a doctor.
get enough sleep. A rested body will work as it should. Sleep at least 7-8 hours a day.
Get a massage. According to experts oriental medicine, there are special points on the body. By acting on them, you can improve your well-being. The point that is located between the nose and the upper lip is responsible for the pressure. Gently massage it with your finger for 2 minutes in a clockwise direction. Do this when you feel weak.

First aid for hypotension and hypertension

If you feel dizzy severe weakness, tinnitus, call an ambulance. In the meantime, the doctors go, act:

Open the collar of your clothes. The neck and chest should be free.
Lie down. Lower your head down. Place a small pillow under your feet.
Smell ammonia. If it is not available, use table vinegar.
Have some tea. Definitely strong and sweet.

If you feel the approach of a hypertensive crisis, then you also need to call the doctors. In general, this disease should always be supported by preventive treatment. As first aid measures, you can resort to the following actions:

Organize a foot bath with hot water, which is pre-added with mustard. An alternative would be to overlay mustard compresses on the region of the heart, neck and calves.
Lightly bind the right, and then the left arm and leg for half an hour each side. When the tourniquet is applied, a pulse should be felt.
Have a drink from chokeberry. It can be wine, compote, juice. Or eat jam from this berry.

To reduce the risk of occurrence and development of hypotension and hypertension, you should adhere to a healthy diet, prevent the appearance excess weight, exclude harmful products from the list, move more.

Pressure should be measured from time to time. When observing a trend of high or low blood pressure, it is recommended to consult a doctor to determine the causes and prescribe treatment. Prescribed therapies may include methods to normalize blood pressure, such as taking special medications and herbal infusions diet, exercise, and so on.

What is atmospheric pressure, definition. Physics Grade 7

The atmosphere extends several thousand kilometers above our planet. Due to the action of gravity, the upper layers of air, like water in the ocean, compress the lower layers, as a result of which the earth's surface and the bodies located on it experience pressure from the entire thickness of the air.
Atmospheric pressure is the pressure exerted by the Earth's atmosphere on all objects on it.

Vyatheslav nasyrov

Atmospheric pressure - the pressure of the atmosphere on all objects in it and the Earth's surface. Atmospheric pressure is created by the gravitational attraction of air to the Earth.
In 1643, Evangelista Torricelli showed that air has weight. Together with V. Viviani, Torricelli conducted the first experiment on measuring atmospheric pressure, inventing the Torricelli tube (the first mercury barometer), a glass tube in which there is no air. In such a tube, mercury rises to a height of about 760 mm.
On the earth's surface, atmospheric pressure varies from place to place and over time. Especially important are the non-periodic changes in atmospheric pressure that determine the weather, associated with the emergence, development and destruction of slowly moving high pressure areas (anticyclones) and relatively fast moving huge eddies (cyclones) in which low pressure prevails. There were fluctuations in atmospheric pressure at sea level within 684 - 809 mm Hg. Art.
Normal atmospheric pressure is a pressure of 760 mm Hg. Art. (101 325 Pa).
Atmospheric pressure decreases as altitude increases, since it is created only by the overlying layer of the atmosphere. The dependence of pressure on height is described by the so-called. barometric formula. The height to which one must rise or fall in order for the pressure to change by 1 hPa is called the baric (barometric) step. Near the earth's surface at a pressure of 1000 hPa and a temperature of 0 °C, it is 8 m/hPa. With an increase in temperature and an increase in altitude above sea level, it increases, that is, it is directly proportional to temperature and inversely proportional to pressure. The reciprocal of the baric step is the vertical baric gradient, i.e., the change in pressure when raising or lowering 100 meters. At a temperature of 0 °C and a pressure of 1000 hPa, it is equal to 12.5 hPa.
On maps, pressure is shown using isobars - lines connecting points with the same surface atmospheric pressure, necessarily reduced to sea level. Atmospheric pressure is measured with a barometer.

Ivan Ivanov

We do not notice the air, because we all live in it. It's hard to imagine, but air has weight in the same way as all bodies on Earth. This is so because gravity acts on it. Air can even be weighed on a scale by placing it in a glass ball. Paragraph forty-two describes how to do this. We do not notice the weight of the air, nature arranged it that way.
Air is held near the Earth by gravity. He does not fly into space thanks to her. The multi-kilometer air shell around the Earth is called the atmosphere. Of course, the atmosphere presses on us and on all other bodies. The pressure of the atmosphere is called atmospheric pressure.
We do not notice it, because the pressure we have inside is the same as the air pressure outside. In the textbook you will find a description of several experiments proving that there is atmospheric pressure. And, of course, try some of them to repeat. Or maybe you can come up with your own or peep on the Internet to show in the lesson, to surprise classmates. There are very entertaining experiments about atmospheric pressure.

What is blood pressure definition?

Blood pressure is the pressure of blood on the walls of blood vessels - veins, arteries and capillaries. Blood pressure is necessary in order to ensure that blood can move through the blood vessels.
The value of arterial pressure (sometimes abbreviated as blood pressure) is determined by the strength of heart contractions, the amount of blood that is ejected into the vessels with each contraction of the heart, the resistance that the walls of blood vessels provide to blood flow and, to a lesser extent, the number of heartbeats per unit time. In addition, the value of blood pressure depends on the amount of blood circulating in the circulatory system, its viscosity. Fluctuations in pressure in the abdominal and thoracic cavities associated with respiratory movements, and other factors.
When blood is forced into the heart, the pressure in it increases until the moment when blood is ejected from the heart into the vessels. These two phases - pumping blood into the heart and pushing it into the vessels - make up, in medical terms, the systole of the heart. Then the heart relaxes, and after a kind of “rest”, it begins to fill with blood again. This stage is called diastole of the heart. Accordingly, the pressure in the vessels has two extreme values: the maximum - systolic, and the minimum - diastolic. And the difference in the value of systolic and diastolic pressure, more precisely, fluctuations in their values, is called pulse pressure. The norm of systolic pressure in large arteries is 110-130 mm Hg, and diastolic pressure is about 90 mm Hg. in the aorta and about 70 mm Hg. in large arteries. These are the same indicators that are known to us under the name of upper and lower pressure.

Muslimgauze

Blood pressure is the pressure that blood exerts on the walls of the blood vessels through which it travels. The value of blood pressure is determined by the strength of heart contractions, the amount of blood and the resistance of blood vessels.
The highest pressure is observed at the time of ejection of blood into the aorta; the minimum - at the moment when the blood reaches the hollow veins. Distinguish between upper (systolic) pressure and lower (diastolic) pressure.

Blood pressure: what is considered normal, how to measure, what to do with high and low?

Mankind owes a lot to the Italian Riva-Rocci, who at the end of the century before last came up with a device that measures blood pressure (BP). At the beginning of the last century, this invention was wonderfully supplemented by the Russian scientist N.S. Korotkov, proposing a technique for measuring pressure in brachial artery phonendoscope. Although Riva-Rocci apparatus was bulky compared to current tonometers and really mercury, but the principle of its operation has not changed for almost 100 years. And the doctors loved him. Unfortunately, now you can only see it in a museum, because compact (mechanical and electronic) devices of a new generation have come to replace it. But auscultatory method N.S. Korotkov is still with us and is successfully used by both doctors and their patients.

Where is the norm?

The norm of blood pressure in adults is considered to be the value120/80 mmHg st. But how can this indicator be fixed if a living organism, which is a person, must constantly adapt to different conditions existence? And people are all different, so within reasonable limits, blood pressure still deviates.

infographic: RIA Novosti

Let modern medicine and abandoned the previous complex formulas for calculating blood pressure, which took into account such parameters as gender, age, weight, but there are still discounts for something. For example, for an asthenic "lightweight" woman, the pressure is 110/70 mm Hg. Art. considered quite normal, and if blood pressure rises by 20 mm Hg. Art., then she will certainly feel it. In the same way, a pressure of 130/80 mm Hg will be the norm. Art. for the trained young man. After all, athletes usually have it.

Fluctuations in blood pressure will still be influenced by factors such as age, physical activity, psycho-emotional environment, climatic and weather. , perhaps, hypertension would not have suffered if he had lived in another country. How else to understand the fact that on the black African continent among the indigenous population of the AG can be found only occasionally, and blacks in the United States suffer from it indiscriminately? It turns out that only BP does not depend on race.

However, if the pressure rises slightly (10 mm Hg) and only to give a person the opportunity to adapt to the environment, that is, occasionally, all this is considered the norm and does not give reason to think about the disease.

With age, blood pressure also rises slightly. This is due to a change in blood vessels that deposit something on their walls. In practically healthy people, the deposits are quite small, so the pressure will increase by 10-15 mm Hg. pillar.

If the blood pressure values cross the line of 140/90 mm Hg. st., will steadfastly hold on to this figure, and sometimes also move upwards, such a person will be diagnosed with arterial hypertension of the appropriate degree, depending on the pressure values. Therefore, for adults there is no norm for blood pressure by age, there is only a small discount for age. But with children, things are a little different.

Video: how to keep blood pressure normal?

And what about children?

Blood pressure in children has different values than adults. And it grows, starting from birth, at first quite quickly, then growth slows down, with some upward jumps in adolescence, and reaches the level of blood pressure of an adult. Of course, it would be surprising if the pressure of such a small newborn child, having everything so "new", was 120/80 mm Hg. Art.

The structure of all organs of a newly born baby has not yet been completed, this also applies to the cardiovascular system. The vessels of the newborn are elastic, their lumen is wider, the network of capillaries is larger, so the pressure is 60/40 mm Hg. Art. it will be the norm for him. Although, perhaps, someone will be surprised by the fact that yellow lipid spots can be found in newborns in the aorta, which, however, do not affect health and disappear with time. But it is, digression.

As the baby develops and the further formation of his body, blood pressure rises and by the year of life the numbers 90-100 / 40-60 mm Hg will be normal. Art., and the child will reach the values of an adult only by the age of 9-10. However, at this age, the pressure is 100/60 mm Hg. Art. will be considered normal and will not surprise anyone. But in adolescents, the normal value of blood pressure is slightly higher than that established for adults 120/80. This is probably due to the hormonal surge characteristic of adolescence. To calculate normal blood pressure values in children, pediatricians use special table which we present to our readers.

Age	Normal minimum systolic pressure	Normal maximum systolic pressure	Normal low diastolic pressure	Normal maximum diastolic pressure
Up to 2 weeks	60	96	40	50
2-4 weeks	80	112	40	74
2-12 months	90	112	50	74
2-3 years	100	112	60	74
3-5 years	100	116	60	76
6-9 years old	100	122	60	78
10-12 years old	110	126	70	82
13-15 years old	110	136	70	86

BP problems in children and adolescents

Unfortunately, such a pathology as arterial hypertension is no exception for child's body. Lability of blood pressure is most often manifested in adolescence, when the body is being restructured, but puberty the more dangerous that a person at this time is not yet an adult, but no longer a child. This age is also difficult for the person himself, because often it leads to pressure surges. instability of the nervous system teenager, and for his parents, and for the attending physician. However, pathological deviations should be noticed and leveled in time. This is the task of adults.

The causes of high blood pressure in children and adolescents can be:

As a result of these factors, vascular tone increases, the heart begins to work with a load, especially its left section. If not accepted urgent action, a young man can meet his majority with a ready-made diagnosis: arterial hypertension or in best case, one type or another.

Measurement of pressure at home

We have been talking about blood pressure for quite some time, implying that all people know how to measure it. It seems nothing complicated, we put a cuff above the elbow, pump air into it, slowly release it and listen.

Everything is correct, but before moving on to the blood pressure of adults, I would like to dwell on the algorithm for measuring blood pressure, since patients often do it on their own and not always according to the method. As a result, inadequate results are obtained, and, accordingly, unreasonable use antihypertensive drugs. In addition, people, talking about upper and lower blood pressure, do not always understand what it all means.

For correct measurement blood pressure is very important in what conditions a person is. In order not to get "random numbers", pressure is measured in America, observing the following rules:

A comfortable environment for a person whose pressure is of interest should be at least 5 minutes;
Do not smoke or eat for half an hour before the manipulation;
Visit the toilet bladder was not filled;
Take into account the voltage pain, bad feeling, medication;
Measure pressure twice on both hands in the prone position, sitting, standing.

Probably, each of us will not agree with this, except perhaps for the military registration and enlistment office or in strict stationary conditions suitable for this measurement. Nevertheless, it is necessary to strive to fulfill at least some points. For example, it would be nice to measure the pressure in calm environment , having comfortably laid or seated a person, take into account the influence of a “good” smoke break or just eaten hearty lunch. It should be remembered that the accepted antihypertensive could not yet have had its effect (little time had passed) and not grasp at next pill seeing disappointing results.

A person, especially if he is not completely healthy, usually does not cope well with measuring pressure on himself (it costs a lot to put on a cuff!). It is better if one of the relatives or neighbors does it. Highly Seriously need treat and to the method of measuring blood pressure.

Video: measuring pressure with an electronic tonometer

Cuff, blood pressure monitor, phonendoscope… systole and diastole

The algorithm for determining blood pressure (N.S. Korotkov's auscultatory method, 1905) is very simple if everything is done correctly. The patient is comfortably seated (you can lie down) and the measurement begins:

Air is released from the cuff connected to the tonometer and the pear, squeezing it with the palms of your hands;
Wrap the cuff around the patient's arm above the elbow (tightly and evenly), trying to keep the rubber connecting tube on the side of the artery, otherwise you can get an incorrect result;
Choose a place to listen and install a phonendoscope;
Inflate the cuff;
The cuff, when air is injected, compresses the arteries due to its own pressure, which is 20-30 mm Hg. Art. above the pressure at which the sounds heard on the brachial artery with each pulse wave completely disappear;
Slowly releasing air from the cuff, listen to the sounds of the artery on the elbow bend;
The first sound heard by the phonendoscope is fixed with a glance on the scale of the tonometer. It will mean a breakthrough of a portion of blood through the clamped area, since the pressure in the artery slightly exceeded the pressure in the cuff. The impact of escaping blood against the wall of an artery is called in Korotkov's tone, top or systolic pressure;
A series of sounds, noises, tones following the systole is understandable to cardiologists, and ordinary people must catch the last sound, which is called diastolic or lower, it is also noted visually.

Thus, contracting, the heart pushes blood into the arteries (systole), creates pressure on them equal to the upper or systolic pressure. Blood begins to be distributed through the vessels, which leads to a decrease in pressure and relaxation of the heart (diastole). This is the last, lower, diastolic beat.

However, there are nuances…

Scientists have found that when measuring blood pressure by the traditional method, its values are 10% different from the true ones (direct measurement in the artery during its puncture). Such an error is more than redeemed by the accessibility and simplicity of the procedure, moreover, as a rule, one measurement of blood pressure in the same patient is not enough, and this makes it possible to reduce the magnitude of the error.

In addition, patients do not differ in the same complexion. For example, in thin people, the determined values are lower. And for full ones, on the contrary, it is higher than in reality. This difference can be leveled by a cuff with a width of more than 130 mm. However, there is not only fat people. Obesity of 3-4 degrees often makes it difficult to measure blood pressure on the arm. In such cases, the measurement is carried out on the leg, using a special cuff for this.

There are cases when, with the auscultatory method of measuring blood pressure in the interval between the upper and lower blood pressure in sound wave there is a break (10-20 mm Hg or more), when there are no sounds above the artery (complete silence), but there is a pulse on the vessel itself. This phenomenon is called auscultatory "failure", which can occur in the upper or middle third of the pressure amplitude. Such a "failure" should not go unnoticed, because then a lower value of blood pressure (the lower limit of the auscultatory "failure") will be mistakenly taken as the value of systolic pressure. Sometimes this difference can even be 50 mm Hg. Art., which, of course, will greatly affect the interpretation of the result and, accordingly, the treatment, if any.

This error is highly undesirable and can be avoided. To do this, simultaneously with the injection of air into the cuff, the pulse should be monitored for radial artery. It is necessary to increase the pressure in the cuff to values \u200b\u200bthat sufficiently exceed the level of disappearance of the pulse.

The phenomenon of "infinite tone" well known to teenage, sports doctors and in military enlistment offices when examining recruits. The nature of this phenomenon is considered to be the hyperkinetic type of blood circulation and low vascular tone, the cause of which is emotional or physical stress. In this case, it is not possible to determine the diastolic pressure, it seems that it is simply equal to zero. However, after a few days, in a relaxed state of a young man, the measurement of the lower pressure presents no difficulty.

Video: traditional pressure measurement

Blood pressure rises ... (hypertension)

The causes of high blood pressure in adults are not much different from those in children, but those who are over ... risk factors, of course, more:

Of course, leading to vasoconstriction and increased blood pressure;
BP clearly correlates with being overweight;
The level of glucose (diabetes mellitus) greatly affects the formation of arterial hypertension;
Excess consumption of table salt;
Life in the city, because it is known that the increase in pressure goes hand in hand with the acceleration of the pace of life;
Alcohol. Strong tea and coffee become the cause only when they are consumed in excessive quantities;
Oral contraceptives, which many women use to avoid unwanted pregnancies;
By itself, smoking might not be among the causes of high blood pressure, but this bad habit too bad effect on blood vessels, especially peripheral ones;
low physical activity;
Professional activity associated with high psycho-emotional stress;
Changes in atmospheric pressure, changes in weather conditions;
Many other diseases, including surgical ones.

People suffering from arterial hypertension, as a rule, control their condition themselves, taking constantly drugs to lower blood pressure, prescribed by a doctor in individually selected dosages. It could be, or. Given the good awareness of patients about their illness, it makes no sense to dwell on arterial hypertension, its manifestations and treatment.

However, everything once begins, and with hypertension. It is necessary to determine whether this is a single increase in blood pressure caused by objective reasons (stress, drinking alcohol in inadequate doses, certain drugs), or there has been a tendency to increase it by permanent basis, for example, blood pressure rises in the evening, after a hard day's work.

It is clear that the nightly rise in blood pressure indicates that during the day a person carries an excessive load for himself, so he must analyze the day, find the cause and begin treatment (or prevention). Even more in such cases, the presence of hypertension in the family should alert, since it is known that this disease has a hereditary predisposition.

If high blood pressure is detected repeatedly, even if in numbers 135/90 mm Hg. Art., it is advisable to start taking measures so that it does not become high. It is not necessary to immediately resort to medications, you can first try to regulate blood pressure by observing the regime of work, rest and nutrition.

A special role in this regard belongs, of course, to diet. By giving preference to products that lower blood pressure, you can long time do without pharmaceuticals, or even avoid taking them altogether, if you do not forget about folk recipes containing medicinal herbs.

By compiling a menu of such affordable products as garlic, white and Brussels sprouts, beans and peas, milk, baked potatoes, salmon fish, spinach, you can eat well and not feel hungry. And bananas, kiwi, orange, pomegranate can perfectly replace any dessert and at the same time normalize blood pressure.

Video: hypertension in the program “Live healthy!”

Blood pressure is low… (hypotension)

Although low blood pressure is not fraught with such formidable complications as high blood pressure, it is uncomfortable for a person to live with him. Typically, these patients have a fairly common diagnosis today - vegetative-vascular (neurocirculatory) dystonia according to hypotonic type, when at the slightest sign Under adverse conditions, blood pressure decreases, which is accompanied by pallor of the skin, dizziness, nausea, general weakness and malaise. Patients are thrown into cold sweat, fainting may occur.

There are a great many reasons for this, the treatment of such people is very difficult and lengthy, besides, there are no drugs for permanent use, except that patients often drink freshly brewed green tea, coffee and occasionally take Eleutherococcus tincture, ginseng and pantocrine tablets. Again, the regimen helps to normalize blood pressure in such patients, and especially sleep, which requires at least 10 hours. Nutrition should be high enough in calories, because low blood pressure requires glucose. Green tea It has a beneficial effect on blood vessels during hypotension, increasing pressure somewhat and thereby bringing a person to life, which is especially noticeable in the morning. A cup of coffee also helps, but be aware of the addictive property of the drink., that is, imperceptibly you can "get hooked" on it.

The complex of recreational activities for low blood pressure includes:

Healthy lifestyle (active rest, sufficient exposure to fresh air);
High physical activity, sports;
Water procedures (aroma baths, hydromassage, swimming pool);
Spa treatment;
Diet;
Elimination of provoking factors.

Help yourself!

If problems with blood pressure have begun, then you should not passively wait for the doctor to come and cure everything. The success of prevention and treatment largely depends on the patient himself. Of course, if you suddenly happen to be in a hospital with a hypertensive crisis, then there they will prescribe a blood pressure profile and pick up pills. But, when a patient comes to an outpatient appointment with complaints of an increased increase in pressure, then a lot will have to be taken on. For example, it is difficult to trace the dynamics of blood pressure from the words, therefore The patient is asked to keep a diary(at the stage of observation for the selection of antihypertensive drugs - a week, during the period long-term use drugs - 2 weeks 4 times a year, that is, every 3 months).

The diary can be an ordinary school notebook, divided into graphs for convenience. It should be remembered that the measurement of the first day, although performed, is not taken into account. In the morning (6-8 hours, but always before taking medication) and in the evening (18-21 hours), 2 measurements should be taken. Of course, it will be better if the patient is so careful that he measures the pressure every 12 hours at the same time.

Rest for 5 minutes, and if there was emotional or physical stress, then 15-20 minutes;
Do not drink strong tea or coffee one hour before the procedure. alcoholic beverages and do not think, do not smoke for half an hour (endure!);
Do not comment on the actions of the measurer, do not discuss the news, remember that there should be silence when measuring blood pressure;
Sit comfortably with your hand on a hard surface.
Carefully enter the values of blood pressure in a notebook, so that later you can show your notes to the attending physician.

You can talk about blood pressure for a long time and a lot, patients are very fond of doing this, sitting under the doctor's office, but you can argue, but you should not take advice and recommendations into service, because everyone has their own cause of arterial hypertension, their own accompanying illnesses and your medicine. For some patients, blood pressure lowering drugs are taken for more than one day, so it is better to trust one person - a doctor.

Video: blood pressure in the program “Live Healthy!”

Man on skis, and without them.

On loose snow, a person walks with great difficulty, sinking deeply at every step. But, having put on skis, he can walk, almost without falling into it. Why? On skis or without skis, a person acts on the snow with the same force equal to his own weight. However, the effect of this force in both cases is different, because the surface area on which the person presses is different, with and without skis. The surface area of the skis is almost 20 times more area soles. Therefore, standing on skis, a person acts on every square centimeter of the snow surface area with a force 20 times less than standing on snow without skis.

The student, pinning a newspaper to the board with buttons, acts on each button with the same force. However, a button with a sharper end is easier to enter into the tree.

This means that the result of the action of a force depends not only on its modulus, direction and point of application, but also on the area of the surface to which it is applied (perpendicular to which it acts).

This conclusion is confirmed by physical experiments.

Experience. The result of this force depends on what force acts per unit area of the surface.

Nails must be driven into the corners of a small board. First, we set the nails driven into the board on the sand with their points up and put a weight on the board. In this case, the nail heads are only slightly pressed into the sand. Then turn the board over and put the nails on the tip. In this case, the area of support is smaller, and under the action of the same force, the nails go deep into the sand.

An experience. Second illustration.

The result of the action of this force depends on what force acts on each unit of surface area.

In the considered examples, the forces acted perpendicular to the surface of the body. The person's weight was perpendicular to the surface of the snow; the force acting on the button is perpendicular to the surface of the board.

The value equal to the ratio of the force acting perpendicular to the surface to the area of \u200b\u200bthis surface is called pressure.

To determine the pressure, it is necessary to divide the force acting perpendicular to the surface by the surface area:

pressure = force / area.

Let us denote the quantities included in this expression: pressure - p, the force acting on the surface, - F and the surface area S.

Then we get the formula:

p = F/S

It is clear that a larger force acting on the same area will produce more pressure.

The pressure unit is taken as the pressure that produces a force of 1 N acting on a surface of 1 m 2 perpendicular to this surface.

Unit of pressure - newton per square meter(1 N / m 2). In honor of the French scientist Blaise Pascal it's called pascal Pa). In this way,

1 Pa = 1 N / m 2.

Other pressure units are also used: hectopascal (hPa) and kilopascal (kPa).

1 kPa = 1000 Pa;

1 hPa = 100 Pa;

1 Pa = 0.001 kPa;

1 Pa = 0.01 hPa.

Let's write down the condition of the problem and solve it.

Given : m = 45 kg, S = 300 cm 2; p = ?

In SI units: S = 0.03 m 2

Solution:

p = F/S,

F = P,

P = g m,

P= 9.8 N 45 kg ≈ 450 N,

p\u003d 450 / 0.03 N / m 2 \u003d 15000 Pa \u003d 15 kPa

"Answer": p = 15000 Pa = 15 kPa

Ways to reduce and increase pressure.

A heavy caterpillar tractor produces a pressure on the soil equal to 40-50 kPa, that is, only 2-3 times more than the pressure of a boy weighing 45 kg. This is because the weight of the tractor is distributed over a larger area due to the caterpillar drive. And we have established that The larger the area of support, the less pressure produced by the same force on this support .

Depending on whether you need to get a small or a large pressure, the area of \u200b\u200bsupport increases or decreases. For example, in order for the soil to withstand the pressure of a building being erected, the area of \u200b\u200bthe lower part of the foundation is increased.

Truck tires and aircraft chassis are made much wider than passenger cars. Particularly wide tires are made for cars designed to travel in deserts.

Heavy machines, like a tractor, a tank or a swamp, having a large bearing area of the tracks, pass through swampy terrain that a person cannot pass through.

On the other hand, with a small surface area, a large pressure can be generated with a small force. For example, pressing a button into a board, we act on it with a force of about 50 N. Since the area of the button tip is approximately 1 mm 2, the pressure produced by it is equal to:

p \u003d 50 N / 0.000001 m 2 \u003d 50,000,000 Pa \u003d 50,000 kPa.

For comparison, this pressure is 1000 times more than the pressure exerted by a caterpillar tractor on the soil. Many more such examples can be found.

The blade of cutting and piercing tools (knives, scissors, cutters, saws, needles, etc.) is specially sharpened. The sharpened edge of a sharp blade has a small area, so even a small force creates a lot of pressure, and it is easy to work with such a tool.

Cutting and piercing devices are also found in wildlife: these are teeth, claws, beaks, spikes, etc. - they are all made of hard material, smooth and very sharp.

Pressure

It is known that gas molecules move randomly.

We already know that gases, unlike solids and liquids, fill the entire vessel in which they are located. For example, a steel cylinder for storing gases, a car tire tube or a volleyball. In this case, the gas exerts pressure on the walls, bottom and lid of the cylinder, chamber or any other body in which it is located. Gas pressure is due to other causes than pressure solid body on a support.

It is known that gas molecules move randomly. During their movement, they collide with each other, as well as with the walls of the vessel in which the gas is located. There are many molecules in the gas, and therefore the number of their impacts is very large. For example, the number of impacts of air molecules in a room on a surface of 1 cm 2 in 1 s is expressed as a twenty-three-digit number. Although the impact force of an individual molecule is small, the action of all molecules on the walls of the vessel is significant - it creates gas pressure.

So, gas pressure on the walls of the vessel (and on the body placed in the gas) is caused by impacts of gas molecules .

Consider the following experience. Place a rubber ball under the air pump bell. It contains a small amount of air and has irregular shape. Then we pump out the air from under the bell with a pump. The shell of the ball, around which the air becomes more and more rarefied, gradually swells and takes the form of a regular ball.

How to explain this experience?

Special durable steel cylinders are used for storage and transportation of compressed gas.

In our experiment, moving gas molecules continuously hit the walls of the ball inside and out. When air is pumped out, the number of molecules in the bell around the shell of the ball decreases. But inside the ball their number does not change. Therefore, the number of impacts of molecules on the outer walls of the shell becomes less than the number of impacts on the inner walls. The balloon is inflated until the force of elasticity of its rubber shell becomes equal to the pressure force of the gas. The shell of the ball takes the shape of a ball. This shows that gas presses on its walls equally in all directions. In other words, the number of molecular impacts per square centimeter of surface area is the same in all directions. The same pressure in all directions is characteristic of a gas and is a consequence of the random movement of a huge number of molecules.

Let's try to reduce the volume of gas, but so that its mass remains unchanged. This means that in each cubic centimeter of gas there will be more molecules, the density of the gas will increase. Then the number of impacts of molecules on the walls will increase, i.e., the gas pressure will increase. This can be confirmed by experience.

On the image a A glass tube is shown, one end of which is covered with a thin rubber film. A piston is inserted into the tube. When the piston is pushed in, the volume of air in the tube decreases, i.e., the gas is compressed. The rubber film bulges outward, indicating that the air pressure in the tube has increased.

On the contrary, with an increase in the volume of the same mass of gas, the number of molecules in each cubic centimeter decreases. This will reduce the number of impacts on the walls of the vessel - the pressure of the gas will become less. Indeed, when the piston is pulled out of the tube, the volume of air increases, the film bends inside the vessel. This indicates a decrease in air pressure in the tube. The same phenomena would be observed if instead of air in the tube there would be any other gas.

So, when the volume of a gas decreases, its pressure increases, and when the volume increases, the pressure decreases, provided that the mass and temperature of the gas remain unchanged.

How does the pressure of a gas change when it is heated at a constant volume? It is known that the speed of movement of gas molecules increases when heated. Moving faster, the molecules will hit the walls of the vessel more often. In addition, each impact of the molecule on the wall will be stronger. As a result, the walls of the vessel will experience more pressure.

Consequently, The pressure of a gas in a closed vessel is greater the higher the temperature of the gas, provided that the mass of the gas and the volume do not change.

From these experiences, one can general conclusion, what the pressure of the gas is greater, the more often and stronger the molecules hit the walls of the vessel .

For storage and transportation of gases, they are highly compressed. At the same time, their pressure increases, gases must be enclosed in special, very durable cylinders. Such cylinders, for example, contain compressed air in submarines, oxygen used in metal welding. Of course, we must always remember that gas cylinders cannot be heated, especially when they are filled with gas. Because, as we already understand, an explosion can occur with very unpleasant consequences.

Pascal's law.

Pressure is transmitted to each point of the liquid or gas.

The pressure of the piston is transmitted to each point of the liquid filling the ball.

Now gas.

Unlike solids, individual layers and small particles of liquid and gas can move freely relative to each other in all directions. It is enough, for example, to lightly blow on the surface of the water in a glass to cause the water to move. Ripples appear on a river or lake at the slightest breeze.

The mobility of gas and liquid particles explains that the pressure produced on them is transmitted not only in the direction of the force, but at every point. Let's consider this phenomenon in more detail.

On the image, a a vessel containing a gas (or liquid) is depicted. The particles are evenly distributed throughout the vessel. The vessel is closed by a piston that can move up and down.

By applying some force, let's make the piston move a little inward and compress the gas (liquid) directly below it. Then the particles (molecules) will be located in this place more densely than before (Fig., b). Due to the mobility of the gas particles will move in all directions. As a result, their arrangement will again become uniform, but more dense than before (Fig. c). Therefore, the pressure of the gas will increase everywhere. This means that additional pressure is transferred to all particles of a gas or liquid. So, if the pressure on the gas (liquid) near the piston itself increases by 1 Pa, then at all points inside gas or liquid pressure will be greater than before by the same amount. The pressure on the walls of the vessel, and on the bottom, and on the piston will increase by 1 Pa.

The pressure exerted on a liquid or gas is transmitted to any point equally in all directions .

This statement is called Pascal's law.

Based on Pascal's law, it is easy to explain the following experiments.

The figure shows a hollow sphere with small holes in various places. A tube is attached to the ball, into which a piston is inserted. If you draw water into the ball and push the piston into the tube, then water will flow from all the holes in the ball. In this experiment, the piston presses on the surface of the water in the tube. The water particles under the piston, condensing, transfer its pressure to other layers lying deeper. Thus, the pressure of the piston is transmitted to each point of the liquid filling the ball. As a result, part of the water is pushed out of the ball in the form of identical streams flowing from all holes.

If the ball is filled with smoke, then when the piston is pushed into the tube, identical streams of smoke will begin to come out of all the holes in the ball. This confirms that and gases transmit the pressure produced on them equally in all directions.

Pressure in liquid and gas.

Under the weight of the liquid, the rubber bottom in the tube will sag.

Liquids, like all bodies on Earth, are affected by the force of gravity. Therefore, each layer of liquid poured into a vessel creates pressure with its weight, which, according to Pascal's law, is transmitted in all directions. Therefore, there is pressure inside the liquid. This can be verified by experience.

Pour water into a glass tube, the bottom hole of which is closed with a thin rubber film. Under the weight of the liquid, the bottom of the tube will bend.

Experience shows that the higher the column of water above the rubber film, the more it sags. But every time after the rubber bottom sags, the water in the tube comes to equilibrium (stops), because, in addition to gravity, the elastic force of the stretched rubber film acts on the water.

Forces acting on the rubber film

are the same on both sides.

Illustration.

The bottom moves away from the cylinder due to the pressure on it due to gravity.

Let's lower a tube with a rubber bottom, into which water is poured, into another, wider vessel with water. We will see that as the tube is lowered, the rubber film gradually straightens out. Full straightening of the film shows that the forces acting on it from above and below are equal. Full straightening of the film occurs when the water levels in the tube and vessel coincide.

The same experiment can be carried out with a tube in which a rubber film closes the side opening, as shown in figure a. Immerse this tube of water into another vessel of water, as shown in the figure, b. We will notice that the film straightens again as soon as the water levels in the tube and vessel are equal. This means that the forces acting on the rubber film are the same from all sides.

Take a vessel whose bottom can fall off. Let's put it in a jar of water. In this case, the bottom will be tightly pressed to the edge of the vessel and will not fall off. It is pressed by the force of water pressure, directed from the bottom up.

We will carefully pour water into the vessel and watch its bottom. As soon as the level of water in the vessel coincides with the level of water in the jar, it will fall away from the vessel.

At the moment of separation, a column of liquid in the vessel presses down on the bottom, and pressure is transmitted from bottom to top to the bottom of the same column of liquid in height, but located in the jar. Both of these pressures are the same, but the bottom moves away from the cylinder due to the action on it own strength gravity.

The experiments with water were described above, but if we take any other liquid instead of water, the results of the experiment will be the same.

So, experiments show that inside the liquid there is pressure, and at the same level it is the same in all directions. Pressure increases with depth.

Gases do not differ in this respect from liquids, because they also have weight. But we must remember that the density of a gas is hundreds of times less than the density of a liquid. The weight of the gas in the vessel is small, and in many cases its "weight" pressure can be ignored.

Calculation of liquid pressure on the bottom and walls of the vessel.

Consider how you can calculate the pressure of a liquid on the bottom and walls of a vessel. Let us first solve the problem for a vessel having the shape of a rectangular parallelepiped.

Strength F, with which the liquid poured into this vessel presses on its bottom, is equal to the weight P the liquid in the vessel. The weight of a liquid can be determined by knowing its mass. m. Mass, as you know, can be calculated by the formula: m = ρ V. The volume of liquid poured into the vessel we have chosen is easy to calculate. If the height of the liquid column in the vessel is denoted by the letter h, and the area of the bottom of the vessel S, then V = S h.

Liquid mass m = ρ V, or m = ρ S h .

The weight of this liquid P = gm, or P = g ρ S h.

Since the weight of the liquid column is equal to the force with which the liquid presses on the bottom of the vessel, then, dividing the weight P To the square S, we get the fluid pressure p:

p = P/S , or p = g ρ S h/S,

We have obtained a formula for calculating the pressure of a liquid on the bottom of a vessel. From this formula it can be seen that the pressure of a liquid at the bottom of a vessel depends only on the density and height of the liquid column.

Therefore, according to the derived formula, it is possible to calculate the pressure of the liquid poured into the vessel any form(Strictly speaking, our calculation is only suitable for vessels having the shape of a straight prism and a cylinder. In physics courses for the institute, it was proved that the formula is also true for a vessel of arbitrary shape). In addition, it can be used to calculate the pressure on the walls of the vessel. The pressure inside the fluid, including pressure from bottom to top, is also calculated using this formula, since the pressure at the same depth is the same in all directions.

When calculating pressure using the formula p = gph need density ρ expressed in kilograms per cubic meter (kg / m 3), and the height of the liquid column h- in meters (m), g\u003d 9.8 N / kg, then the pressure will be expressed in pascals (Pa).

Example. Determine the oil pressure at the bottom of the tank if the height of the oil column is 10 m and its density is 800 kg/m 3 .

Let's write down the condition of the problem and write it down.

Given :

ρ \u003d 800 kg / m 3

Solution :

p = 9.8 N/kg 800 kg/m 3 10 m ≈ 80,000 Pa ≈ 80 kPa.

Answer : p ≈ 80 kPa.

Communicating vessels.

The figure shows two vessels connected to each other by a rubber tube. Such vessels are called communicating. A watering can, a teapot, a coffee pot are examples of communicating vessels. We know from experience that water poured, for example, into a watering can, always stands at the same level in the spout and inside.

Communicating vessels are common to us. For example, it can be a teapot, a watering can or a coffee pot.

The surfaces of a homogeneous liquid are installed at the same level in communicating vessels of any shape.

Liquids of various densities.

With communicating vessels, the following simple experiment can be done. At the beginning of the experiment, we clamp the rubber tube in the middle, and pour water into one of the tubes. Then we open the clamp, and the water instantly flows into the other tube until the water surfaces in both tubes are at the same level. You can fix one of the tubes in a tripod, and raise, lower or tilt the other in different directions. And in this case, as soon as the liquid calms down, its levels in both tubes will equalize.

In communicating vessels of any shape and section, the surfaces of a homogeneous liquid are set at the same level(provided that the air pressure over the liquid is the same) (Fig. 109).

This can be justified as follows. The liquid is at rest without moving from one vessel to another. This means that the pressures in both vessels are the same at any level. The liquid in both vessels is the same, that is, it has the same density. Therefore, its heights must also be the same. When we raise one vessel or add liquid to it, the pressure in it increases and the liquid moves into another vessel until the pressures are balanced.

If a liquid of one density is poured into one of the communicating vessels, and another density is poured into the second, then at equilibrium the levels of these liquids will not be the same. And this is understandable. We know that the pressure of a liquid on the bottom of a vessel is directly proportional to the height of the column and the density of the liquid. And in this case, the densities of the liquids will be different.

With equal pressures, the height of a liquid column with a higher density will be less than the height of a liquid column with a lower density (Fig.).

An experience. How to determine the mass of air.

Air weight. Atmosphere pressure.

existence of atmospheric pressure.

Atmospheric pressure is greater than the pressure of rarefied air in a vessel.

The force of gravity acts on the air, as well as on any body located on the Earth, and, therefore, the air has weight. The weight of air is easy to calculate, knowing its mass.

We will show by experience how to calculate the mass of air. To do this, take a strong glass ball with a cork and a rubber tube with a clamp. We pump air out of it with a pump, clamp the tube with a clamp and balance it on the scales. Then, opening the clamp on the rubber tube, let air into it. In this case, the balance of the scales will be disturbed. To restore it, you will have to put weights on the other pan of scales, the mass of which will be equal to the mass of air in the volume of the ball.

Experiments have established that at a temperature of 0 ° C and normal atmospheric pressure, the mass of air with a volume of 1 m 3 is 1.29 kg. The weight of this air is easy to calculate:

P = g m, P = 9.8 N/kg 1.29 kg ≈ 13 N.

The air envelope that surrounds the earth is called atmosphere (from Greek. atmosphere steam, air, and sphere- ball).

The atmosphere, as shown by observations of the flight of artificial Earth satellites, extends to a height of several thousand kilometers.

Due to the action of gravity, the upper layers of the atmosphere, like ocean water, compress the lower layers. The air layer adjacent directly to the Earth is compressed the most and, according to Pascal's law, transfers the pressure produced on it in all directions.

As a result of this, the earth's surface and the bodies on it experience the pressure of the entire thickness of the air, or, as is usually said in such cases, experience Atmosphere pressure .

The existence of atmospheric pressure can be explained by many phenomena that we encounter in life. Let's consider some of them.

The figure shows a glass tube, inside which there is a piston that fits snugly against the walls of the tube. The end of the tube is dipped in water. If you raise the piston, then the water will rise behind it.

This phenomenon is used in water pumps and some other devices.

The figure shows a cylindrical vessel. It is closed with a cork into which a tube with a tap is inserted. Air is pumped out of the vessel by a pump. The end of the tube is then placed in water. If you now open the tap, then the water will splash into the inside of the vessel in a fountain. Water enters the vessel because the atmospheric pressure is greater than the pressure of rarefied air in the vessel.

Why does the air shell of the Earth exist.

Like all bodies, the molecules of gases that make up the air envelope of the Earth are attracted to the Earth.

But why, then, do they not all fall to the surface of the Earth? How is the air shell of the Earth, its atmosphere, preserved? To understand this, we must take into account that the molecules of gases are in continuous and random motion. But then another question arises: why these molecules do not fly away into the world space, that is, into space.

In order to completely leave the Earth, a molecule, like a spacecraft or a rocket, must have a very high speed (at least 11.2 km/s). This so-called second escape velocity. The speed of most molecules in the Earth's air envelope is much less than this cosmic speed. Therefore, most of them are tied to the Earth by gravity, only a negligible number of molecules fly beyond the Earth into space.

The random movement of molecules and the effect of gravity on them result in the fact that gas molecules "float" in space near the Earth, forming an air shell, or the atmosphere known to us.

Measurements show that air density decreases rapidly with altitude. So, at a height of 5.5 km above the Earth, the air density is 2 times less than its density at the Earth's surface, at a height of 11 km - 4 times less, etc. The higher, the rarer the air. And finally, in the most upper layers(hundreds and thousands of kilometers above the Earth), the atmosphere gradually turns into airless space. The air shell of the Earth does not have a clear boundary.

Strictly speaking, due to the action of gravity, the density of the gas in any closed vessel is not the same throughout the entire volume of the vessel. At the bottom of the vessel, the density of the gas is greater than in its upper parts, and therefore the pressure in the vessel is not the same. It is larger at the bottom of the vessel than at the top. However, for the gas contained in the vessel, this difference in density and pressure is so small that in many cases it can be completely ignored, just be aware of it. But for an atmosphere extending over several thousand kilometers, the difference is significant.

Measurement of atmospheric pressure. The Torricelli experience.

It is impossible to calculate atmospheric pressure using the formula for calculating the pressure of a liquid column (§ 38). For such a calculation, you need to know the height of the atmosphere and the density of the air. But the atmosphere does not have a definite boundary, and the air density at different heights is different. However, atmospheric pressure can be measured using an experiment proposed in the 17th century by an Italian scientist. Evangelista Torricelli a student of Galileo.

Torricelli's experiment is as follows: a glass tube about 1 m long, sealed at one end, is filled with mercury. Then, tightly closing the second end of the tube, it is turned over and lowered into a cup with mercury, where this end of the tube is opened under the level of mercury. As in any liquid experiment, part of the mercury is poured into the cup, and part of it remains in the tube. The height of the mercury column remaining in the tube is approximately 760 mm. There is no air above the mercury inside the tube, there is an airless space, so no gas exerts pressure from above on the mercury column inside this tube and does not affect the measurements.

Torricelli, who proposed the experience described above, also gave his explanation. The atmosphere presses on the surface of the mercury in the cup. Mercury is in balance. This means that the pressure in the tube is aa 1 (see figure) is equal to atmospheric pressure. When atmospheric pressure changes, the height of the mercury column in the tube also changes. As the pressure increases, the column lengthens. As the pressure decreases, the mercury column decreases in height.

The pressure in the tube at the level aa1 is created by the weight of the mercury column in the tube, since there is no air above the mercury in the upper part of the tube. Hence it follows that atmospheric pressure is equal to the pressure of the mercury column in the tube , i.e.

p atm = p mercury.

The greater the atmospheric pressure, the higher the mercury column in Torricelli's experiment. Therefore, in practice, atmospheric pressure can be measured by the height of the mercury column (in millimeters or centimeters). If, for example, atmospheric pressure is 780 mm Hg. Art. (they say "millimeters of mercury"), this means that the air produces the same pressure as a vertical column of mercury 780 mm high produces.

Therefore, in this case, 1 millimeter of mercury (1 mm Hg) is taken as the unit of atmospheric pressure. Let's find the relationship between this unit and the unit known to us - pascal(Pa).

The pressure of a mercury column ρ of mercury with a height of 1 mm is:

p = g ρ h, p\u003d 9.8 N / kg 13,600 kg / m 3 0.001 m ≈ 133.3 Pa.

So, 1 mm Hg. Art. = 133.3 Pa.

Currently, atmospheric pressure is usually measured in hectopascals (1 hPa = 100 Pa). For example, weather reports may announce that the pressure is 1013 hPa, which is the same as 760 mmHg. Art.

Observing daily the height of the mercury column in the tube, Torricelli discovered that this height changes, that is, atmospheric pressure is not constant, it can increase and decrease. Torricelli also noticed that atmospheric pressure is related to changes in the weather.

If you attach a vertical scale to the mercury tube used in Torricelli's experiment, you get the simplest device - mercury barometer (from Greek. baros- heaviness, metreo- measure). It is used to measure atmospheric pressure.

Barometer - aneroid.

In practice, a metal barometer is used to measure atmospheric pressure, called aneroid (translated from Greek - aneroid). The barometer is called so because it does not contain mercury.

The appearance of the aneroid is shown in the figure. Its main part is a metal box 1 with a wavy (corrugated) surface (see other fig.). Air is pumped out of this box, and so that atmospheric pressure does not crush the box, its cover 2 is pulled up by a spring. As atmospheric pressure increases, the lid flexes downward and tensions the spring. When the pressure decreases, the spring straightens the cover. An arrow-pointer 4 is attached to the spring by means of a transmission mechanism 3, which moves to the right or left when the pressure changes. A scale is fixed under the arrow, the divisions of which are marked according to the indications of a mercury barometer. Thus, the number 750, against which the aneroid arrow stands (see Fig.), shows that in this moment in a mercury barometer, the height of the mercury column is 750 mm.

Therefore, atmospheric pressure is 750 mm Hg. Art. or ≈ 1000 hPa.

The value of atmospheric pressure is very important for predicting the weather for the coming days, since changes in atmospheric pressure are associated with changes in the weather. A barometer is a necessary instrument for meteorological observations.

Atmospheric pressure at various altitudes.

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

The situation is more complicated with gases. Gases are highly compressible. And the more the gas is compressed, the greater its density, and the greater the pressure it produces. After all, the pressure of a gas is created by the impact of its molecules on the surface of the body.

The layers of air near the surface of the Earth are compressed by all the overlying layers of air above them. But the higher the layer of air from the surface, the weaker it is compressed, the lower its density. Hence, the less pressure it produces. If, for example, a balloon rises above the surface of the Earth, then the air pressure on the balloon becomes less. This happens not only because the height of the air column above it decreases, but also because the air density decreases. It is smaller at the top than at the bottom. Therefore, the dependence of air pressure on altitude is more complicated than that of liquids.

Observations show that atmospheric pressure in areas lying at sea level is on average 760 mm Hg. Art.

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

normal atmospheric pressure equals 101 300 Pa = 1013 hPa.

The higher the altitude, the lower the pressure.

With small rises, on average, for every 12 m of rise, the pressure decreases by 1 mm Hg. Art. (or 1.33 hPa).

Knowing the dependence of pressure on altitude, it is possible to determine the height above sea level by changing the readings of the barometer. Aneroids having a scale on which you can directly measure the height above sea level are called altimeters . They are used in aviation and when climbing mountains.

Pressure gauges.

We already know that barometers are used to measure atmospheric pressure. To measure pressures greater or less than atmospheric pressure, the pressure gauges (from Greek. manos- rare, inconspicuous metreo- measure). Pressure gauges are liquid and metal.

Consider first the device and action open liquid manometer. It consists of a two-legged glass tube into which some liquid is poured. The liquid is installed in both knees at the same level, since only atmospheric pressure acts on its surface in the knees of the vessel.

To understand how such a pressure gauge works, it can be connected with a rubber tube to a round flat box, one side of which is covered with a rubber film. If you press your finger on the film, then the liquid level in the manometer knee connected in the box will decrease, and in the other knee it will increase. What explains this?

Pressing on the film increases the air pressure in the box. According to Pascal's law, this increase in pressure is transferred to the liquid in that knee of the pressure gauge, which is attached to the box. Therefore, the pressure on the liquid in this knee will be greater than in the other, where only atmospheric pressure acts on the liquid. Under the force of this excess pressure, the liquid will begin to move. In the knee with compressed air, the liquid will fall, in the other it will rise. The liquid will come to equilibrium (stop) when the excess pressure of the compressed air is balanced by the pressure that the excess liquid column produces in the other leg of the pressure gauge.

The stronger the pressure on the film, the higher the excess liquid column, the greater its pressure. Consequently, the change in pressure can be judged by the height of this excess column.

The figure shows how such a pressure gauge can measure the pressure inside a liquid. The deeper the tube is immersed in the liquid, the greater the difference in the heights of the liquid columns in the manometer knees becomes., so, therefore, and fluid produces more pressure.

If you install the device box at some depth inside the liquid and turn it with a film up, sideways and down, then the pressure gauge readings will not change. That's the way it should be, because at the same level inside a liquid, the pressure is the same in all directions.

The picture shows metal manometer . The main part of such a pressure gauge is a metal tube bent into a pipe 1 , one end of which is closed. The other end of the tube with a tap 4 communicates with the vessel in which the pressure is measured. As pressure increases, the tube flexes. Movement of its closed end with a lever 5 and gears 3 passed to the shooter 2 moving around the scale of the instrument. When the pressure decreases, the tube, due to its elasticity, returns to its previous position, and the arrow returns to zero division of the scale.

Piston liquid pump.

In the experiment we considered earlier (§ 40), it was found that water in a glass tube, under the action of atmospheric pressure, rose up behind the piston. This action is based piston pumps.

The pump is shown schematically in the figure. It consists of a cylinder, inside which goes up and down, tightly adhering to the walls of the vessel, the piston 1 . Valves are installed in the lower part of the cylinder and in the piston itself. 2 opening only upwards. When the piston moves upwards, water enters the pipe under the action of atmospheric pressure, lifts the bottom valve and moves behind the piston.

When the piston moves down, the water under the piston presses on the bottom valve, and it closes. At the same time, under pressure from the water, a valve inside the piston opens, and the water flows into the space above the piston. With the next movement of the piston upwards, the water above it also rises in the place with it, which pours out into the outlet pipe. At the same time, a new portion of water rises behind the piston, which, when the piston is subsequently lowered, will be above it, and this whole procedure is repeated again and again while the pump is running.

Hydraulic Press.

Pascal's law allows you to explain the action hydraulic machine (from Greek. hydraulicos- water). These are machines whose action is based on the laws of motion and equilibrium of liquids.

The main part of the hydraulic machine is two cylinders of different diameters, equipped with pistons and a connecting tube. The space under the pistons and the tube are filled with liquid (usually mineral oil). The heights of the liquid columns in both cylinders are the same as long as there are no forces acting on the pistons.

Let us now assume that the forces F 1 and F 2 - forces acting on the pistons, S 1 and S 2 - areas of pistons. The pressure under the first (small) piston is p 1 = F 1 / S 1 , and under the second (large) p 2 = F 2 / S 2. According to Pascal's law, the pressure of a fluid at rest is transmitted equally in all directions, i.e. p 1 = p 2 or F 1 / S 1 = F 2 / S 2 , from where:

F 2 / F 1 = S 2 / S 1 .

Therefore, the strength F 2 so much more power F 1 , How many times greater is the area of the large piston than the area of the small piston?. For example, if the area of the large piston is 500 cm 2, and the small one is 5 cm 2, and a force of 100 N acts on the small piston, then a force 100 times greater will act on the larger piston, that is, 10,000 N.

Thus, with the help of a hydraulic machine, it is possible to balance a large force with a small force.

Attitude F 1 / F 2 shows the gain in strength. For example, in the example above, the gain in force is 10,000 N / 100 N = 100.

The hydraulic machine used for pressing (squeezing) is called hydraulic press .

Hydraulic presses are used where a lot of power is required. For example, for squeezing oil from seeds at oil mills, for pressing plywood, cardboard, hay. Steel mills use hydraulic presses to make steel machine shafts, railway wheels, and many other products. Modern hydraulic presses can develop a force of tens and hundreds of millions of newtons.

The device of the hydraulic press is shown schematically in the figure. The body to be pressed 1 (A) is placed on a platform connected to a large piston 2 (B). The small piston 3 (D) creates a large pressure on the liquid. This pressure is transmitted to every point of the fluid filling the cylinders. Therefore, the same pressure acts on the second, large piston. But since the area of the 2nd (large) piston is larger than the area of the small one, then the force acting on it will be greater than the force acting on piston 3 (D). Under this force, piston 2 (B) will rise. When piston 2 (B) rises, the body (A) rests against the fixed upper platform and is compressed. The pressure gauge 4 (M) measures the fluid pressure. Safety valve 5 (P) automatically opens when the fluid pressure exceeds the allowable value.

From the small cylinder to large liquid pumped by repeated movements of the small piston 3 (D). This is done in the following way. When the small piston (D) is lifted, valve 6 (K) opens and liquid is sucked into the space under the piston. When the small piston is lowered under the action of liquid pressure, valve 6 (K) closes, and valve 7 (K") opens, and the liquid passes into a large vessel.

The action of water and gas on a body immersed in them.

Under water, we can easily lift a stone that can hardly be lifted in the air. If you submerge the cork under water and release it from your hands, it will float. How can these phenomena be explained?

We know (§ 38) that the liquid presses on the bottom and walls of the vessel. And if some solid body is placed inside the liquid, then it will also be subjected to pressure, like the walls of the vessel.

Consider the forces that act from the side of the liquid on the body immersed in it. To make it easier to reason, we choose a body that has the shape of a parallelepiped with bases parallel to the surface of the liquid (Fig.). The forces acting on the side faces of the body are equal in pairs and balance each other. Under the influence of these forces, the body is compressed. But the forces acting on the upper and lower faces of the body are not the same. On the upper face presses from above with force F 1 column of liquid tall h one . At the level of the lower face, the pressure produces a liquid column with a height h 2. This pressure, as we know (§ 37), is transmitted inside the liquid in all directions. Therefore, on the lower face of the body from the bottom up with a force F 2 presses a liquid column high h 2. But h 2 more h 1 , hence the modulus of force F 2 more power modules F one . Therefore, the body is pushed out of the liquid with a force F vyt, equal to the difference of forces F 2 - F 1 , i.e.

But S·h = V, where V is the volume of the parallelepiped, and ρ W ·V = m W is the mass of fluid in the volume of the parallelepiped. Consequently,

F vyt \u003d g m well \u003d P well,

i.e. buoyant force is equal to the weight of the liquid in the volume of the body immersed in it(The buoyant force is equal to the weight of a liquid of the same volume as the volume of the body immersed in it).

The existence of a force that pushes a body out of a liquid is easy to discover experimentally.

On the image a shows a body suspended from a spring with an arrow pointer at the end. The arrow marks the tension of the spring on the tripod. When the body is released into the water, the spring contracts (Fig. b). The same contraction of the spring will be obtained if you act on the body from the bottom up with some force, for example, press it with your hand (raise it).

Therefore, experience confirms that a force acting on a body in a fluid pushes the body out of the fluid.

For gases, as we know, Pascal's law also applies. That's why bodies in the gas are subjected to a force pushing them out of the gas. Under the influence of this force, the balloons rise up. The existence of a force pushing a body out of a gas can also be observed experimentally.

We hang a glass ball or a large flask closed with a cork to a shortened scale pan. The scales are balanced. Then a wide vessel is placed under the flask (or ball) so that it surrounds the entire flask. The vessel is filled with carbon dioxide, the density of which is greater than the density of air (therefore, carbon dioxide sinks down and fills the vessel, displacing air from it). In this case, the balance of the scales is disturbed. A cup with a suspended flask rises up (Fig.). A flask immersed in carbon dioxide experiences a greater buoyant force than that which acts on it in air.

The force that pushes a body out of a liquid or gas is directed opposite to the force of gravity applied to this body.

Therefore, prolcosmos). This explains why in the water we sometimes easily lift bodies that we can hardly keep in the air.

A small bucket and a cylindrical body are suspended from the spring (Fig., a). The arrow on the tripod marks the extension of the spring. It shows the weight of the body in the air. Having lifted the body, a drain vessel is placed under it, filled with liquid to the level of the drain tube. After that, the body is completely immersed in the liquid (Fig., b). Wherein part of the liquid, the volume of which is equal to the volume of the body, is poured out from a pouring vessel into a glass. The spring contracts and the pointer of the spring rises to indicate the decrease in the weight of the body in the fluid. In this case, in addition to the force of gravity, another force acts on the body, pushing it out of the fluid. If the liquid from the glass is poured into the upper bucket (i.e., the one that was displaced by the body), then the spring pointer will return to its initial position (Fig., c).

Based on this experience, it can be concluded that the force that pushes a body completely immersed in a liquid is equal to the weight of the liquid in the volume of this body . We reached the same conclusion in § 48.

If a similar experiment were done with a body immersed in some gas, it would show that the force pushing the body out of the gas is also equal to the weight of the gas taken in the volume of the body .

The force that pushes a body out of a liquid or gas is called Archimedean force, in honor of the scientist Archimedes who first pointed to its existence and calculated its significance.

So, experience has confirmed that the Archimedean (or buoyant) force is equal to the weight of the fluid in the volume of the body, i.e. F A = P f = g m and. The mass of liquid m f , displaced by the body, can be expressed in terms of its density ρ w and the volume of the body V t immersed in the liquid (since V l - the volume of the liquid displaced by the body is equal to V t - the volume of the body immersed in the liquid), i.e. m W = ρ W V t. Then we get:

F A= g ρ and · V t

Therefore, the Archimedean force depends on the density of the liquid in which the body is immersed, and on the volume of this body. But it does not depend, for example, on the density of the substance of a body immersed in a liquid, since this quantity is not included in the resulting formula.

Let us now determine the weight of a body immersed in a liquid (or gas). Since the two forces acting on the body in this case are directed in opposite directions (gravity is down, and the Archimedean force is up), then the weight of the body in fluid P 1 will be less than the weight of the body in vacuum P = gm to the Archimedean force F A = g m w (where m w is the mass of liquid or gas displaced by the body).

In this way, if a body is immersed in a liquid or gas, then it loses in its weight as much as the liquid or gas displaced by it weighs.

Example. Determine the buoyant force acting on a stone with a volume of 1.6 m 3 in sea water.

Let's write down the condition of the problem and solve it.

When the floating body reaches the surface of the liquid, then with its further upward movement, the Archimedean force will decrease. Why? But because the volume of the part of the body immersed in the liquid will decrease, and the Archimedean force is equal to the weight of the liquid in the volume of the part of the body immersed in it.

When the Archimedean force becomes equal to the force of gravity, the body will stop and float on the surface of the liquid, partially immersed in it.

The resulting conclusion is easy to verify experimentally.

Pour water into the drain vessel up to the level of the drain pipe. After that, let's immerse the floating body into the vessel, having previously weighed it in the air. Having descended into the water, the body displaces a volume of water equal to the volume of the part of the body immersed in it. Having weighed this water, we find that its weight (Archimedean force) is equal to the force of gravity acting on a floating body, or the weight of this body in air.

Having done the same experiments with any other bodies floating in different liquids - in water, alcohol, salt solution, you can make sure that if a body floats in a liquid, then the weight of the liquid displaced by it is equal to the weight of this body in air.

It is easy to prove that if the density of a solid solid is greater than the density of a liquid, then the body sinks in such a liquid. A body with a lower density floats in this liquid. A piece of iron, for example, sinks in water but floats in mercury. The body, on the other hand, whose density is equal to the density of the liquid, remains in equilibrium inside the liquid.

Ice floats on the surface of water because its density is less than that of water.

The lower the density of the body compared to the density of the liquid, the smaller part of the body is immersed in the liquid .

With equal densities of the body and liquid, the body floats inside the liquid at any depth.

Two immiscible liquids, for example water and kerosene, are located in a vessel in accordance with their densities: in the lower part of the vessel - denser water (ρ = 1000 kg / m 3), on top - lighter kerosene (ρ = 800 kg / m 3) .

The average density of living organisms inhabiting the aquatic environment differs little from the density of water, so their weight is almost completely balanced by the Archimedean force. Thanks to this, aquatic animals do not need such strong and massive skeletons as terrestrial ones. For the same reason, the trunks of aquatic plants are elastic.

The swim bladder of a fish easily changes its volume. When the fish descends to a great depth with the help of muscles, and the water pressure on it increases, the bubble contracts, the volume of the fish's body decreases, and it does not push upwards, but swims in the depths. Thus, the fish can, within certain limits, regulate the depth of its dive. Whales regulate their diving depth by contracting and expanding their lung capacity.

Sailing ships.

Ships floating on rivers, lakes, seas and oceans are built from different materials with different densities. The hull of ships is usually made of steel sheets. All internal fasteners that give ships strength are also made of metals. For the construction of ships, various materials are used, which, compared with water, have both higher and lower densities.

How do ships float, take on board and carry large loads?

An experiment with a floating body (§ 50) showed that the body displaces so much water with its underwater part that this water is equal in weight to the weight of the body in air. This is also true for any ship.

The weight of water displaced by the underwater part of the ship is equal to the weight of the ship with cargo in the air or the force of gravity acting on the ship with cargo.

The depth to which a ship is submerged in water is called draft . The deepest allowable draft is marked on the ship's hull with a red line called waterline (from Dutch. water- water).

The weight of water displaced by the ship when submerged to the waterline, equal to the force of gravity acting on the ship with cargo, is called the displacement of the ship.

At present, ships with a displacement of 5,000,000 kN (5 10 6 kN) and more are being built for the transportation of oil, i.e., having a mass of 500,000 tons (5 10 5 t) and more together with the cargo.

If we subtract the weight of the ship itself from the displacement, then we get the carrying capacity of this ship. Carrying capacity shows the weight of the cargo carried by the ship.

Shipbuilding existed in Ancient Egypt, in Phoenicia (it is believed that the Phoenicians were one of the best shipbuilders), Ancient China.

In Russia, shipbuilding originated at the turn of the 17th and 18th centuries. Mainly warships were built, but it was in Russia that the first icebreaker, ships with an engine internal combustion, nuclear icebreaker "Arktika".

Aeronautics.

Drawing describing the ball of the Montgolfier brothers in 1783: “View and exact dimensions"Globe Balloon", which was the first". 1786

Since ancient times, people have dreamed of being able to fly above the clouds, to swim in the ocean of air, as they sailed on the sea. For aeronautics

At first, balloons were used, which were filled either with heated air, or with hydrogen or helium.

In order for a balloon to rise into the air, it is necessary that the Archimedean force (buoyancy) F A, acting on the ball, was more than gravity F heavy, i.e. F A > F heavy

As the ball rises, the Archimedean force acting on it decreases ( F A = gρV), since the density of the upper atmosphere is less than that of the Earth's surface. To rise higher, a special ballast (weight) is dropped from the ball and this lightens the ball. Eventually the ball reaches its maximum lift height. To lower the ball, part of the gas is released from its shell using a special valve.

AT horizontal direction the balloon moves only under the influence of the wind, so it is called balloon (from Greek air- air, stato- standing). Not so long ago, huge balloons were used to study the upper layers of the atmosphere, the stratosphere - stratostats .

Before they learned how to build large aircraft for transporting passengers and cargo by air, controlled balloons were used - airships. They have an elongated shape, a gondola with an engine is suspended under the body, which drives the propeller.

The balloon not only rises by itself, but can also lift some cargo: a cabin, people, instruments. Therefore, in order to find out what kind of load a balloon can lift, it is necessary to determine it. lifting force.

Let, for example, a balloon with a volume of 40 m 3 filled with helium be launched into the air. The mass of helium filling the shell of the ball will be equal to:
m Ge \u003d ρ Ge V \u003d 0.1890 kg / m 3 40 m 3 \u003d 7.2 kg,
and its weight is:
P Ge = g m Ge; P Ge \u003d 9.8 N / kg 7.2 kg \u003d 71 N.
The buoyant force (Archimedean) acting on this ball in the air is equal to the weight of air with a volume of 40 m 3, i.e.
F A \u003d g ρ air V; F A \u003d 9.8 N / kg 1.3 kg / m 3 40 m 3 \u003d 520 N.

This means that this ball can lift a load weighing 520 N - 71 N = 449 N. This is its lifting force.

A balloon of the same volume, but filled with hydrogen, can lift a load of 479 N. This means that its lifting force is greater than that of a balloon filled with helium. But still, helium is used more often, since it does not burn and is therefore safer. Hydrogen is a combustible gas.

It is much easier to raise and lower a balloon filled with hot air. For this, a burner is located under the hole located in the lower part of the ball. Using a gas burner, you can control the temperature of the air inside the ball, which means its density and buoyancy. In order for the ball to rise higher, it is enough to heat the air in it more strongly, increasing the flame of the burner. When the burner flame decreases, the temperature of the air in the ball decreases, and the ball goes down.

It is possible to choose such a temperature of the ball at which the weight of the ball and the cabin will be equal to the buoyancy force. Then the ball will hang in the air, and it will be easy to make observations from it.

As science developed, there were also significant changes in aeronautical technology. It became possible to use new shells for balloons, which became durable, frost-resistant and light.

Achievements in the field of radio engineering, electronics, automation made it possible to design unmanned balloons. These balloons are used to study air currents, for geographical and biomedical research in the lower layers of the atmosphere.

The man is complex mechanism, in the body of which all processes are interconnected. Blood pressure is one of the important indicators of health, its sudden changes can cause serious complications in the form of a stroke, myocardial infarction or coronary disease. Each person should know what factors provoke a change in pressure, how to properly measure it, and how preventive measures follow to normalize it.

What is blood pressure?

Blood pressure is the level of blood pressure on the walls of the arteries in the body. This is an individual indicator, its changes can be influenced by:

the person's age;
stressful situations;
the presence of chronic pathologies;
Times of Day;

Exists average rate arterial blood pressure 120/80 mm Hg. Art., from which doctors are repelled in the process of diagnosing a patient. Pressure is measured in millimeters of mercury and shows two numbers - upper and lower pressure.

Blood pressure is one of the most important indicators of human health

Upper (systolic) - the pressure exerted by the blood at the time of maximum contraction of the heart.
Lower (diastolic) - blood pressure at the moment of maximum relaxation of the heart muscle.

Deviations of 20-30 mm Hg. Art. above or below the average of 120/80 mm Hg. Art. in an adult indicates possible diseases. Timely treatment will protect against the transition of the disease into a chronic form and from severe complications.

Everyone should know about blood pressure and what it is to prevent possible diseases.

Mechanism of arterial regulation

In the human body, all processes are interconnected. The mechanism of arterial regulation is very complex, it is influenced by such things as the central and autonomic nervous system, endocrine system person.

The pressure fluctuates within its normal range due to such factors:

The movement of blood through the vessels (hemodynamics). Responsible for the level of blood pressure.
Neurohumoral regulation. Nervous and humoral regulation are common system, which has a regulating effect on the pressure level.

Blood pressure (BP) is the force exerted by blood on the walls of the arteries.

The nervous system reacts with lightning speed to changes in the body. During physical activity, mental stress and stress, the sympathetic nervous system activates the excitation of cardiac activity and affects the speed of the heartbeat, which causes a change in pressure.

The kidneys perform important function to maintain blood pressure, they remove water and electrolytes from the body.

The kidneys secrete hormones and substances that are important humoral regulators:

They produce renin. This hormone is part of the renin-angiotensin system, which regulates pressure in the body, affects blood volume and vascular tone.
Form depressant substances. With the help of them, the arteries expand and the pressure decreases.

Methods and rules for measuring indicators

Pressure can be measured directly indirect method. The direct (invasive) method of measuring pressure is used in the inpatient treatment of a patient, when constant monitoring of the indicator is needed. It is produced using a catheter, the needle of which is inserted into the patient's lumen of the radial artery. The catheter itself is attached to a manometer to obtain pressure readings.

To measure blood pressure, classic tonometers with a phonendoscope are used.

The indirect (non-invasive) method of measuring pressure does not require direct contact with the bloodstream:

auscultatory or auditory method. Produced by a mechanical tonometer with a phonendoscope. The cuff squeezes the artery with the help of pumped air and the indicators are listened to in the form of noise that is emitted when blood passes through the artery.
Oscillometric method. It does not require noise listening and the indicators are displayed on the display of a digital tonometer. The most common measurement method, which requires a minimum of effort and is convenient for daily use at home in the form of an electronic tonometer.

To get the correct readings of the tonometer when measuring pressure, you must follow these rules:

Blood pressure is measured in a sitting or lying position.
The patient should be in a relaxed state, not talking.
An hour before the measurement, you need to exclude food intake, two hours - alcohol and cigarettes.
The cuff worn on the arm is fixed at the level of the heart.
If the tonometer is semi-automatic, air is injected smoothly and without sudden movements.
The rolled-up sleeve of clothing should not squeeze the arm during the measurement process.

The normal blood pressure of a person directly depends on his age, lifestyle

The first home pressure measurements are best done on both hands. The hand on which the indicators turn out to be higher is used for constant measurements. It is believed that the pressure in right-handers will be higher on the left hand, in left-handers - on the right hand.

Arterial hypotension: symptoms and treatment

Systematic pressure with an indicator below 100/60 mm Hg. Art. called arterial hypotension.

Most of all, teenagers and young girls are prone to it. The main symptoms of hypotension include:

dizziness;
fast fatigue;
lethargy;
nausea;
insomnia;
cardiopalmus.

In the process of treatment, the specialist must establish the root cause that affects the decrease in pressure.

Although low blood pressure is not fraught with such formidable complications as high blood pressure, it is uncomfortable for a person to live with him.

Together with the treatment of the underlying disease, drug treatment is prescribed:

psychomotor stimulants. These drugs activate nervous system, they stimulate efficiency and relieve lethargy, increase heart rate and increase blood pressure ("Sindocarb", "Mezokarb").
analeptic drugs. Increase blood circulation in the process of excitation of the vasomotor center back section brain. These drugs increase the efficiency and mood of a person ("Cordiamin").
Alpha-agonists. They increase vascular tone, cause narrowing of arterioles ("Gutron", "Midodrin").

Each of the described medicines has its own number side effects Therefore, it should be prescribed under the strict supervision of a physician. Hypotensives need to take the time physical activity and prolonged sleep, a contrast shower is also recommended.

Products that increase blood pressure and improve the condition of the body hypotonic:

coffee;
strong tea;
nuts;
cheeses.

A cup of coffee helps, but be aware of the addictive property of the drink.

Hypertension: manifestations and principles of treatment

Elevated constant blood pressure 139/89 mm Hg. Art. is one of the most common diseases of the cardiovascular system.

Older people with diseases of the heart and blood vessels are most prone to hypertension. But the appearance of elevated blood pressure in people over 30 years of age is not ruled out.

Risk factors for developing hypertension include:

systematic stress;
excess weight;
heredity;
age over 55;
diabetes;
elevated cholesterol levels;
kidney failure;
constant smoking and alcohol consumption.

The latent course of hypertension or the initial stage of the disease can be suspected if periodically noted: headaches

In order for the treatment to be effective, in parallel with hypertension, the doctor will treat its root cause. When treating elderly hypertensive patients, it is important that the doctor knows the general condition of the sick patient and his weak sides. They are prescribed medications with a minimum number of side effects, so that the drugs do not affect the work of already diseased organs and do not worsen his health.

The following medications can help lower high blood pressure:

Diuretics. They are prescribed to remove excess salt and fluid from the body, which contribute to an increase in pressure. Potassium-containing diuretics, together with the liquid, do not remove potassium important for the body, and thiazide-type diuretics have a low number of side effects on the body (Aldactone, Indapamide).
Beta blockers. By decreasing the amount of adrenaline, these medicines decrease the heart rate. In its work, adrenaline is interconnected with beta-adrenergic receptors, the work of which is blocked by these medicines (Concor, Vasocardin).
calcium antagonists. Such drugs dilate blood vessels and increase blood flow in the body. The decrease in pressure occurs due to inhibition of the flow of calcium ions into the heart and blood vessels of the patient ("Lomir", "Norvask").

Therapeutic measures for hypertension may include both pharmacological and non-pharmacological methods.

Pressure in children and adolescents

During the period of growth and puberty, the body of a child and adolescent undergoes active restructuring and changes. Indicator 120/80 mm Hg. Art. refers to a fully formed person, and normal indicators in children and adolescents will be underestimated. So, the pressure is 105/60 mm Hg. Art. considered normal for a child of 6-10 years.

We all had our blood pressure taken. Almost everyone knows that normal rate pressure is 120/80 mmHg. But not everyone can answer what these numbers actually mean.

Let's try to figure out what upper / lower pressure generally means, as well as how these values differ from each other. First, let's define the concepts.

Blood pressure (BP) is one of the most important indicators, it demonstrates the functioning of the circulatory system. This indicator is formed with the participation of the heart, blood vessels and blood moving through them.

Blood pressure is the pressure of blood on the wall of an artery

Moreover, it depends on the resistance of the blood, its volume, "ejected" as a result of one contraction (this is called systole), and the intensity of the contractions of the heart. The highest blood pressure can be observed when the heart contracts and "ejects" blood from the left ventricle, and the lowest - during entry into the right atrium, when the main muscle is relaxed (diastole). Here we come to the most important.

Under the upper pressure or, in the language of science, systolic, refers to the pressure of the blood during contraction. This indicator shows how the heart contracts. The formation of such pressure is carried out with the participation of large arteries (for example, the aorta), and depends this indicator from a number of key factors.

These include:

stroke volume of the left ventricle;
distensibility of the aorta;
maximum ejection speed.

As for the lower pressure (in other words, diastolic), it shows what resistance the blood experiences while moving through the blood vessels. Lower pressure occurs when the aortic valve closes and blood cannot return to the heart. In this case, the heart itself is filled with other blood, saturated with oxygen, and prepares for the next contraction. The movement of blood occurs as if by gravity, passively.

Factors that affect diastolic pressure include:

heart rate;
peripheral vascular resistance.

Note! AT normal condition the difference between the two indicators ranges between 30 mm and 40 mm of mercury, although much here depends on the well-being of the person. Despite the fact that there are specific figures and facts, each organism is individual, as well as its blood pressure.

We conclude: in the example given at the beginning of the article (120/80), 120 is an indicator of upper blood pressure, and 80 is lower.

Blood pressure - norm and deviations

Characteristically, the formation of blood pressure depends mainly on lifestyle, nutritious diet, habits (including bad ones), the frequency of stress. For example, by eating a particular food, you can specifically lower / increase blood pressure. It is authentically known that there were cases when people were completely cured of hypertension after changing their habits and lifestyle.

Why do you need to know the value of blood pressure?

For every 10 mmHg increase, the risk of cardiovascular disease increases by about 30 percent. People with high blood pressure are seven times more likely to have a stroke, four times more ischemic diseases heart, in two - damage to the blood vessels of the lower extremities.

That is why finding out the cause of symptoms such as dizziness, migraines or general weakness should begin with measuring blood pressure. In some cases, the pressure must be constantly monitored and checked every few hours.

How pressure is measured

In most cases, blood pressure is measured using a special device consisting of the following elements:

pneumocuff for arm compression;
manometer;
pear with a control valve designed for pumping air.

The cuff is placed over the shoulder. During the measurement process, it is necessary to adhere to certain requirements, otherwise the result may be incorrect (underestimated or overestimated), which, in turn, may affect the subsequent treatment tactics.

Blood pressure - measurement

The cuff should fit the size of the arm. For people with overweight and children use special cuffs.
The environment should be comfortable, the temperature should be room temperature, and you should start at least after a five-minute rest. If it is cold, vascular spasms will occur and the pressure will rise.
You can perform the procedure only half an hour after eating, coffee or smoking.
Before the procedure, the patient sits down, leans on the back of the chair, relaxes, his legs at this time should not be crossed. The hand should also be relaxed and lie motionless on the table until the end of the procedure (but not on the "weight").
No less important is the height of the table: it is necessary that the fixed cuff is located at the level of approximately the fourth intercostal space. For each five-centimeter displacement of the cuff in relation to the heart, the indicator will decrease (if the limb is raised) or increase (if lowered) by 4 mmHg.
During the procedure, the pressure gauge scale should be at eye level - so there will be less chance of making a mistake when reading.
Air is pumped into the cuff so that the internal pressure in it exceeds the estimated systolic blood pressure by at least 30 mmHg. If the pressure in the cuff is too high, pain may occur and, as a result, blood pressure may change. Air should be discharged at a speed of 3-4 mmHg per second, tones are heard with a tonometer or stethoscope. It is important that the head of the device does not press too hard on the skin - this can also distort the readings.
During reset, the appearance of a tone (this is called the first phase of Korotkoff tones) will correspond to top pressure. When, upon subsequent listening, the tones disappear altogether (fifth phase), the resulting value will correspond to the lower pressure.
A few minutes later, another measurement is taken. The average value obtained from several consecutive measurements reflects the state of affairs more accurately than a single procedure.
The first measurement is recommended to be carried out on both hands at once. Then you can use one hand - the one on which the pressure is higher.

Note! If a person has a heart rhythm disorder, then measuring blood pressure will be a more complicated procedure. Therefore, it is better that a medical officer does this.

How to evaluate your blood pressure

The higher a person's blood pressure, the Great chance the appearance of such ailments as stroke, ischemia, renal failure, etc. For an independent assessment of the pressure indicator, you can use a special classification developed back in 1999.

Table number 1. Assessment of the level of blood pressure. Norm

* - optimal in terms of the development of vascular and heart diseases, as well as mortality.

Note! If the upper and lower blood pressure are in different categories, then the one that is higher is selected.

Table number 2. Assessment of the level of blood pressure. Hypertension

Pressure	Upper pressure, mmHg	Lower pressure, mmHg
First degree	140 to 159	90 to 99
Second degree	160 to 179	100 to 109
Third degree	Over 180	Over 110
Border Degree	140 to 149	Up to 90
Systolic hypertension	Over 140	Up to 90