Why are measurements necessary in science. The subject of physics. Why is the study of physics so important to humanity? Old Russian measures
Lesson outline on the topic " »
date :
Theme: « Scientific-practical conference “Why do we need measurements in science?»
Objectives:
Educational : formation of skills to generalize and systematize educational material on the chapter "Physical methods of cognition of nature";
Developing : development of skills to explain the thermal expansion of bodies;
Educational : instill a culture of mental work, accuracy, teach to see the practical use of knowledge, continue the formation of communication skills, educate attentiveness, observation.
Lesson type: generalization and systematization of knowledge
Equipment and sources of information:
Isachenkova, L.A. Physics: textbook. for 7 cl. institutions total. Wednesday education with rus. lang. training / L. A. Isachenkova, G. V. Palchik, A. A. Sokolsky; ed. A. A. Sokolsky. Minsk: Narodnaya Asveta, 2017.
Lesson structure:
Organizational moment (2 min)
Basic knowledge update (5 min)
Consolidation of knowledge (33 min)
Lesson summary (5 min)
Lesson content
Organizing time
Today we are conducting a lesson in the form of a scientific and practical conference. How do you think today's lesson will differ from the traditional ones?
The result of our scientific and practical conference will be a discussion of the following issues:
first, the old measurement system;
secondly, to figure out what measuring instruments exist,
thirdly, the history of the thermometer,
fourthly, to show the role of measurements in science and human life.
Updating basic knowledge
Answer the questions (frontal survey):
What is called the thermal expansion of bodies?
Give examples of thermal expansion (contraction) of solids, liquids, gases.
What is the difference between thermal expansion of gases and thermal expansion of solids and liquids?
Consolidation of knowledge
(we will consolidate knowledge in the form of a round table)
Dear conference participants and our guests! We are glad to welcome you to this class! In a few minutes you will be able to listen to reports on“The role of measurements in human life and science”.
I suggest the following work plan:
Speeches by speakers.
Opponents' opinions.
Summing up the results of the conference.
If there is no objection, then we start.
Student speech
Physical education
And now the floor is given to opponents.
Each opponent has a score sheet (Appendix 1)
Lesson summary
(Closing remarks or summing up the results of the conference)
We will not be satisfied with what has already been achieved and will continue this work. I ask you to express your opinion in the student assessment cards issued to you so that it can be taken into account in preparation for the next conference.
During the conference and at the end of the conference, the jury fills out the assessment card(Appendix 2). The assessment is made on a 10-point system. The jury sums up and announces the results of the conference.
Reflection
Continue phrases:
Today in the lesson I learned ...
It was interesting…
The knowledge that I gained in the lesson will come in handy.
Appendix 1
Evaluation paper
Project name
Name of the student
Criteria for evaluation
final grade
Relevance of the topic
Sources of information
Idea development quality
Originality and creativity
Registration of work
Project defense
Appendix 2
Speaker Scorecard
F.I. studentlaconic presentation of the main idea (duration of speech is no more than 5 minutes), consistency and evidence of reasoning, their connection with the topic of the work
competent use of technical terminology
the ability to highlight and substantiate the purpose and objectives of the work, as well as the main and the secondary; demonstrate the results of analysis and generalization, independence
level of complexity of work, amount of knowledge and skills in the basic discipline
completeness and clarity of answers to questions on the fundamentals of physics discussed in the work and
Total
As I write at my desk, I can reach up to turn on the lamp, or down to open the drawer and reach for the pen. Stretching out my hand forward, I touch a small and strange-looking statuette, which my sister gave me for luck. Reaching back, I can pat the black cat sneaking behind my back. On the right are notes taken during research for the article, on the left are a bunch of things to do (bills and correspondence). Up, down, forward, backward, right, left - I control myself in my personal space of three-dimensional space. The invisible axes of this world are imposed on me by the rectangular structure of my office, defined, like most Western architecture, by three right angles put together.
Our architecture, education and vocabularies tell us about the three-dimensionality of space. The Oxford English Dictionary is space: “a continuous area or space, free, available or not occupied by anything. Measurements of height, depth and width, within which all things exist and move. " [ ozhegov's vocabulary is similar: “Extension, a place not limited by visible limits. The gap between something, the place where something is. fits. " / approx. transl.]. In the 18th century, he argued that three-dimensional Euclidean space is an a priori necessity, and we, oversaturated with computer-generated images and video games, are constantly reminded of this representation in the form of a seemingly axiomatic rectangular coordinate system. From the point of view of the 21st century, this already seems almost self-evident.
And yet the idea of \u200b\u200bliving in a space described by some kind of mathematical structure is a radical innovation of Western culture that made it necessary to refute ancient beliefs about the nature of reality. Although the birth of modern science is often described as a transition to a mechanized description of nature, perhaps the more important aspect of it - and certainly longer - was the transition to the concept of space as a geometric construction.
In the last century, the problem of describing the geometry of space has become the main project of theoretical physics, in which experts, starting with Albert Einstein, tried to describe all the fundamental interactions of nature as by-products of the shape of space itself. Although at the local level we have been taught to think of space as three-dimensional, general relativity describes a four-dimensional universe, and string theory speaks of ten dimensions - or 11, if we take its extended version, M-theory, as a basis. There are versions of this theory with 26 dimensions, and recently mathematicians have enthusiastically adopted the one describing 24 dimensions. But what are these "dimensions"? And what does the presence of ten dimensions in space mean?
To arrive at a modern mathematical understanding of space, one must first think of it as some kind of arena that matter can occupy. At the very least, space must be imagined as something extended. Such an idea, even if it is obvious to us, would seem heretical, whose concepts of representing the physical world prevailed in Western thinking in late antiquity and the Middle Ages.
Strictly speaking, Aristotelian physics did not include the theory of space, but only the concept of place. Consider a cup of tea on a table. For Aristotle, the cup was surrounded by air, which itself was a kind of substance. In his picture of the world there was no such thing as empty space - there were only boundaries between substances - a cup and air. Or a table. For Aristotle, space, if you want to call it that, was only an infinitely thin line between the cup and what surrounds it. The base of extension space was not something that could be something else inside.
From a mathematical point of view, “dimension” is just another coordinate axis, another degree of freedom, which becomes a symbolic concept, not necessarily related to the material world. In the 1860s, logic pioneer Augustus de Morgan, whose work influenced Lewis Carroll, summarized this increasingly abstract field by noting that mathematics is purely a “science of symbols,” and as such does not have to be associated with anything. except for herself. Mathematics, in a sense, is logic that moves freely in the fields of imagination.
Unlike mathematicians who play freely in the fields of ideas, physicists are tied to nature, and, at least in principle, depend on material things. But all these ideas lead us to a liberating possibility - after all, if mathematics allows for more than three dimensions, and we believe that mathematics is useful for describing the world, how do we know that physical space is limited to three dimensions? Although Galileo, Newton, and Kant took length, width, and height as axioms, couldn't there be more dimensions in our world?
Again, the idea of \u200b\u200ba universe with more than three dimensions penetrated the consciousness of society through the artistic environment, this time - through literary reasoning, the most famous of which is the work of the mathematician "" (1884). This charming social satire tells the story of a humble Square living on a plane, to which one day the three-dimensional creature Lord Sphere comes to visit, leading him into the magnificent world of three-dimensional bodies. In this paradise of volumes, the Square observes its three-dimensional version, the Cube, and begins to dream about the transition to the fourth, fifth and sixth dimensions. Why not a hypercube? Or not a hyper-hypercube, he thinks?
Unfortunately, in Flatland, the Square is considered a lunatic and locked up in an insane asylum. One of the moral of the story, in contrast to its more corny adaptations and adaptations, is the danger lurking in ignoring social foundations. The square, talking about other dimensions of space, talks about other changes in being - it becomes a mathematical eccentric.
At the end of the 19th and the beginning of the 20th centuries, a lot of authors (Herbert Wells, mathematician and author of science fiction novels, who coined the word "tesseract" for a four-dimensional cube), artists (Salvador Dali) and mystics ([ russian occultist, philosopher, theosophist, tarologist, journalist and writer, mathematician by education / approx. transl.] studied ideas related to the fourth dimension and what an encounter with it can become for a person.
Then in 1905, then-unknown physicist Albert Einstein published a paper describing the real world as four-dimensional. In his "special theory of relativity", time was added to the three classical dimensions of space. In the mathematical formalism of relativity, all four dimensions are linked together - this is how the term "space-time" entered our lexicon. This unification was not arbitrary. Einstein discovered that by using this approach, it was possible to create a powerful mathematical apparatus that surpassed Newton's physics and allowed him to predict the behavior of electrically charged particles. Electromagnetism can be fully and accurately described only in a four-dimensional model of the world.
Relativity has become much more than just another literary playespecially when Einstein expanded it from “special” to “general”. Multidimensional space has acquired a deep physical meaning.
In Newton's picture of the world, matter moves through space in time under the influence of natural forces, in particular, gravity. Space, time, matter and forces are different categories of reality. With SRT, Einstein demonstrated the unification of space and time, reducing the number of fundamental physical categories from four to three: space-time, matter and forces. General relativity takes the next step, weaving gravity into the structure of space-time itself. From a four-dimensional perspective, gravity is just an artifact of the shape of space.
To understand this remarkable situation, consider its two-dimensional counterpart. Imagine a trampoline drawn on the surface of a Cartesian plane. Now let's place the bowling ball on the grid. Around it, the surface will stretch and distort so that some points move away from each other more. We have distorted the internal measure of distance in space, made it uneven. General relativity says that heavy objects, such as the Sun, subject space-time to just such a distortion, and a deviation from the Cartesian perfection of space leads to the appearance of a phenomenon that we perceive as gravity.
In Newtonian physics, gravity appears out of nowhere, while in Einstein it naturally arises from the internal geometry of a four-dimensional manifold. Where the manifold stretches the most, or departs from Cartesian regularity, gravity is felt more strongly. This is sometimes referred to as "rubber film physics." In it, the enormous cosmic forces that keep planets in orbits around stars, and stars in orbits within galaxies, are nothing more than a side effect of distorted space. Gravity is literally geometry in action.
If going into four-dimensional space helps explain gravity, will there be any scientific advantage to fifth-dimensional space? Why not try it? asked a young Polish mathematician in 1919, reflecting on the fact that if Einstein included gravity in space-time, then perhaps an extra dimension could similarly treat electromagnetism as an artifact of space-time geometry. So Kaluza added an extra dimension to Einstein's equations, and to his delight, he found that in five dimensions, both of these forces are beautifully artifacts of the geometric model.
The mathematics magically converges, but in this case, the problem was that the extra dimension did not correlate in any way with any particular physical property. In general relativity, the fourth dimension was time; in Kaluza's theory, it was not something to see, feel, or point to: it just was in mathematics. Even Einstein became disillusioned with such an ephemeral innovation. What is it? he asked; where is it?
There are many versions of string theory equations describing ten-dimensional space, but in the 1990s a mathematician at the Institute for Advanced Study at Princeton (Einstein's old lair) showed that things could be simplified a little by moving to an 11-dimensional perspective. He called his new theory "M-theory", and mysteriously refused to explain what the letter "M" stands for. Usually they say that it means "membrane", but besides this, there were also such proposals as "matrix", "master", "mystical" and "monstrous".
So far, we have no evidence for these extra dimensions - we are still in a state of floating physicists dreaming of inaccessible miniature landscapes - but string theory has had a powerful impact on mathematics itself. Recently, the development of a 24-dimensional version of this theory has shown an unexpected relationship between several major branches of mathematics, which means that even if string theory is not useful in physics, it will be a useful resource. In mathematics, 24-dimensional space is special - magical things happen there, for example, it is possible to pack spheres in a particularly elegant way - although it is unlikely that there are 24 dimensions in the real world. For the world we live in and love, most string theorists believe that 10 or 11 dimensions will be enough.
There is another development in string theory worthy of note. In 1999 (the first woman to receive a post at Harvard in theoretical physics) and (American theoretical physicist of particles of Indian origin), that an extra dimension could exist on the cosmological scale, on the scales described by the theory of relativity. According to their theory, "brane" (brane is an abbreviation for membrane) - what we call our Universe may be located in a much larger five-dimensional space, in something like a superuniverse. In this super-space, our universe may be one of a number of co-existing universes, each of which is a four-dimensional bubble in the broader arena of five-dimensional space.
It's hard to say if we will ever be able to confirm Randall and Sandrum's theory. However, some analogies are already being drawn between this idea and the dawn of modern astronomy. 500 years ago, Europeans thought it impossible to imagine other physical "worlds" besides our own, but now we know that the Universe is filled with billions of other planets moving in orbits around billions of other stars. Who knows, maybe someday our descendants will be able to find evidence for the existence of billions of other universes, each of which has its own unique equations for space-time.
The project of understanding the geometric structure of space is one of the characteristic achievements of science, but it may turn out that physicists have reached the end of this path. It turns out that Aristotle was right in a sense - the idea of \u200b\u200ban extended space does have logical problems. Despite all the extraordinary successes of the theory of relativity, we know that its description of space cannot be final, since it fails at the quantum level. Over the past half century, physicists have tried unsuccessfully to combine their understanding of space on a cosmological scale with what they observe on a quantum scale, and it increasingly seems that such fusion may require radically new physics.
Einstein, after developing general relativity, spent most of his life trying to "express all the laws of nature from the dynamics of space and time, reducing physics to pure geometry," as Robbert Dijkgraaf, director of the Institute for Advanced Study at Princeton, recently said. "For Einstein, space-time was the natural foundation of an endless hierarchy of scientific objects." Like Newton, Einstein's picture of the world puts space at the head of existence, makes it an arena in which everything happens. But on a tiny scale, where quantum properties dominate, the laws of physics show that the kind of space we are used to may not exist.
Some theoretical physicists are beginning to argue that space may be some kind of emerging phenomenon, resulting from something more fundamental, just as temperature arises on a macroscopic scale as a result of the movement of molecules. As Dijkgraaf puts it, "The current view is that spacetime is not a point of reference, but a final finish line, a natural structure that emerges from the complexity of quantum information."
A leading proponent of new ways of representing space is the Caltech cosmologist, recently that classical space is not “a fundamental part of the architecture of reality,” and arguing that we are wrongly assigning this special status to its four, or 10, or 11 dimensions. If Dijkgraaf makes an analogy with temperature, then Carroll invites us to consider "moisture", a phenomenon that manifests itself because many water molecules come together. Individual water molecules are not wet, and the property of moisture appears only when you collect many of them in one place. Likewise, he says, space emerges from more basic things on a quantum level.
Carroll writes that from a quantum point of view, the Universe "appears in a mathematical world with the number of dimensions of the order of 10 10 100" - it is a dozen with a googol of zeros, or 10,000 and another trillion trillion trillion trillion trillion trillion trillion trillion zeros. It is difficult to imagine such an impossibly huge number, in comparison with which the number of particles in the Universe is completely insignificant. And yet, each of them is a separate dimension in mathematical space, described by quantum equations; each is a new "degree of freedom" available to the universe.
Even Descartes would have been amazed at where his reasoning took us, and what an amazing complexity was hidden in such a simple word as "dimension."
Khamatova Dilyara
As a child, we often hear proverbs that use old words. For example: "From a pot two tops, and already a pointer", "Seven spans in the forehead", "Each merchant measures his own yardstick", "Slanting fathom in the shoulders", "Kolomenskaya verst".
In literature lessons, we study classical works in which ancient words are encountered, and in mathematics lessons, various units of measurement.
Probably everyone will find a steelyard, a ruler and a measuring tape at home. They are needed in order to measure weight and length. There are other measuring devices at home. This is a clock by which they know the time, a thermometer, which everyone will glance at when going out into the street, an electricity meter, by which they find out how much to pay for it at the end of the month, and much more.
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Introduction
Why does a person need measurements?
As a child, we often hear proverbs that use old words. For instance:"From a pot two tops, and already a pointer", "Seven spans in the forehead", "Each merchant measures his yardstick", "Slanting fathom in the shoulders", "Kolomenskaya verst".
In literature lessons, we study classical works in which ancient words are encountered, and in mathematics lessons, various units of measurement.
Probably everyone will find a steelyard, a ruler and a measuring tape at home. They are needed in order to measure weight and length. There are other measuring devices at home. This is a clock by which they know the time, a thermometer that everyone will glance at when going out into the street, an electricity meter, by which they will know how much to pay for it at the end of the month, and much more.
The first units for measuring quantities were not very accurate. For example: distances were measured in steps. Of course, the size of the step is different for different people, but they took some average value. For measuring long distances, the step was too small a unit.
Step is the distance between the heels or toes of a walking person. Average stride length 71 cm.
The word "degree" - Latin, means "step", "step". Measurement of angles in degrees appeared more than 3 thousand years ago in Babylon. The sixagesimal number system was used in the calculations.
The old Russian system of measures took shape approximately in the 10th - 11th centuries. Its main units are a verst, fathom, elbow and span.
The smallest of them is a span. This word means a hand (remember the modern word "wrist"). The span was defined as the distance between the ends of the extended thumb and forefinger, its value is approximately equal to 18-19 cm.
The elbow is a larger unit, as in most states, it was a unit equal to the distance from the elbow to the end of the extended middle finger. The Old Russian cubit was approximately 46 - 47 cm. It was the main unit in the trade in canvas, linen and other fabrics.
In the 18th century, the measures were specified. Peter I, by decree, established the equality of three-arshin fathoms to seven English feet. The former Russian system of measures of length, supplemented by new measures, received its final form:
Mile \u003d 7 versts (\u003d 7, 47 km);
Verst \u003d 500 fathoms (\u003d 1.07 km);
Fathom \u003d 3 arshins \u003d 7 feet (2.13 m);
Arshin \u003d 16 inches \u003d 28 inches (71.12 cm);
Foot \u003d 12 inches (30.48 cm);
Inch \u003d 10 lines (2.54 cm);
Line \u003d 10 points (2, 54cm).
Very often, while reading literary works, we come across ancient measures of measurement of quantities and do not always have an idea of \u200b\u200bwhat they mean. For example, these are well-known fairy tales: Thumbelina, the tale of Tsar Saltan, the Little Humpbacked Horse, Alice through the Looking Glass, the Sleeping Beauty, Little Muk, and in the poems of A.S. Pushkin, K.I. Chukovsky and many other works.
“Yes, I’ll also make a face of a skate
Only 3 inches tall,
On the back with two humps
Yes with arshin ears ”. (Ershov)
"And the good fairy who saved his daughter
from death, wishing her a hundred years' sleep,
was at that time far away
12 thousand miles from the castle. But she immediately found out about
this is a misfortune from a little dwarf runner who had seven-league boots. "
"What do you want? - chocolate.
For whom? - for my son.
How much to send?
- yes pounds that way 5 or 6:
He can't eat anymore.
I have it small! "
Meanwhile how far away he is
It beats long and hard
The term of the motherland is coming;
God gave them a son in an arshin ...
Ancient measures and tasks.
"Arithmetic" L.F.Magnitsky
Problem number 1.
On a hot day, 6 mowers drankkad * kvass in 8 hours. You need to find out how many mowers will drink the same kadi of kvass in 3 hours.
______________________________________
* Kadi - a cylindrical container made of wooden rivets (planks) and covered with metal or wooden hoops
Decision:
1) How many mowers will drink kadi in one hour?
6x8 \u003d 48 (mowers)
2) How many mowers will drink kadi in three hours?
48: 3 \u003d 16 (mowers)
Answer: 16 mowers will drink kadi kvass in 3 hours.
conclusions
I got acquainted with the texts of ancient mathematical problems from "Arithmetic" by Magnitsky
I also learned the old measures of length (span, elbow,verst, sazhen, arshin,;weight (pood, pound), volume (quarter, caddy their compliance with modern measures.I saw that in the old textbook much attention was paid to entertaining problems, to which LF Magnitsky devoted a whole section entitled "On some comforting actions through the arithmetic used."
I examined literary works in which there are ancient units of measurement, and I was convinced that there are a lot of them.
Science begins ever since
how they begin to measure ...
D. I. Mendeleev
Ponder the words of a famous scientist. The role of measurements in any science, and especially in physics, is clear from them. But, in addition, measurements are important in practical life. Can you imagine your life without measurements of time, mass, length, vehicle speed, power consumption, etc.?
How to measure a physical quantity? Measuring instruments are used for this purpose. Some of them are already known to you. These are different types of rulers, clocks, thermometers, scales, protractor (Fig. 20), etc.
Figure: 20
Measuring instruments are digital and scale... In digital instruments, the measurement result is determined by numbers. This is an electronic clock (Fig. 21), a thermometer (Fig. 22), an electricity meter (Fig. 23), etc.
Figure: 21
Figure: 22
Figure: 23
A ruler, an analogue clock, a household thermometer, scales, a protractor (see Fig. 20) are scale instruments. They have a scale. The measurement result is determined from it. The entire scale is outlined by divisions (Fig. 24). One division is not one stroke (as students sometimes mistakenly believe). This is the gap between the two nearest strokes. In Figure 25, there are two divisions between the numbers 10 and 20, and the dashes are 3. The devices that we will use in laboratory work are mostly scale.
Figure: 24
Figure: 25
To measure a physical quantity means to compare it with a homogeneous quantity taken as a unit.
For example, to measure the length of a straight line segment between points A and B, you need to attach a ruler and, using a scale (Fig. 26), determine how many millimeters fit between points A and B. The homogeneous value with which the length of segment AB was compared was a length equal to 1 mm.
Figure: 26
If a physical quantity is measured directly by taking data off the scale of the device, then such a measurement is called direct.
For example, by applying a ruler to a bar in different places, we will determine its length a (Fig. 27, a), width b and height c. We determined the value of length, width, height directly by removing the reading from the ruler scale. From Figure 27, b it follows: a \u003d 28 mm. This is a direct measurement.
Figure: 27
How to determine the volume of a bar?
It is necessary to carry out direct measurements of its length a, width b and height c, and then using the formula
V \u003d a. b. c
calculate the volume of the bar.
In this case, we say that the volume of the bar was determined by the formula, that is, indirectly, and the measurement of the volume is called indirect measurement.
Figure: 28
Think and answer
- Figure 28 shows several measuring instruments.
- What are these measuring devices called?
- Which ones are digital?
- What physical quantity does each device measure?
- What is the homogeneous value on the scale of each device shown in Figure 28, with which the measured value is compared?
- Please resolve the dispute.
Tanya and Petya solve the problem: “Determine with a ruler the thickness of one sheet of a book containing 300 pages. The thickness of all sheets is 3 cm. " Petya claims that this can be done by directly measuring the sheet thickness with a ruler. Tanya believes that determining the thickness of the sheet is an indirect measurement.
What do you think? Justify your answer.
Interesting to know!
By studying the structure of the human body and the work of its organs, scientists also carry out many measurements. It turns out that a person weighing about 70 kg has about 6 liters of blood. The human heart in a calm state beats 60-80 times per minute. For one contraction, it emits an average of 60 cm 3 of blood, about 4 liters per minute, about 6-7 tons per day, and more than 2000 tons per year. So our heart is a great worker!
Human blood passes through the kidneys 360 times a day, being cleansed of harmful substances there. The total length of the renal blood vessels is 18 km. By leading a healthy lifestyle, we help our body to function smoothly!
Homework
Figure: 29
- List the measuring devices in your notebook that are in your apartment (house). Divide them into groups:
1) digital; 2) scale.
- Check the validity of the rule of Leonardo da Vinci (Fig. 29) - a brilliant Italian artist, mathematician, astronomer, engineer. For this:
- measure your height: ask someone to use a triangle (fig. 30) to put a small line on the doorframe in pencil; measure the distance from the floor to the marked line;
- measure the distance along a horizontal line between the ends of the fingers (fig. 31);
- compare the value obtained in point b) with your height; for most people, these values \u200b\u200bare equal, which was first noticed by Leonardo da Vinci.
Figure: thirty
Figure: 31
To acquaint with the device and the principle of operation of the aneroid barometer and teach how to use it.
Promote the development of the ability to connect natural phenomena with physical laws.
Continue the formation of ideas about atmospheric pressure and the relationship between atmospheric pressure and the altitude above sea level.
Continue to foster an attentive, benevolent attitude towards the participants of the educational process, personal responsibility for the performance of collective work, an understanding of the need to take care of the cleanliness of the atmospheric air and observe the rules of nature protection, the acquisition of everyday skills.
Imagine an air-filled, sealed cylinder with a piston mounted on top. If you start to press on the piston, the volume of air in the cylinder will begin to decrease, air molecules will collide with each other and with the piston more and more intensively, and the pressure of compressed air on the piston will increase.
If the piston is now suddenly released, then the compressed air will force it up sharply. This will happen because with a constant area of \u200b\u200bthe piston, the force acting on the piston from the compressed air side will increase. The area of \u200b\u200bthe piston remained unchanged, and the force from the gas molecules increased, and the pressure increased accordingly.
Or another example. A man stands on the ground, stands with both feet. In this position, a person is comfortable, he does not experience any inconvenience. But what happens if this person decides to stand on one leg? He will bend one of his legs at the knee, and now he will rest on the ground with only one foot. In this position, a person will feel some discomfort, because the pressure on the foot has increased, and approximately 2 times. Why? Because the area through which the force of gravity now pushes a person to the ground has decreased by 2 times. Here's an example of what pressure is and how easily it can be found in everyday life.
Physics pressure
From the point of view of physics, pressure is a physical quantity that is numerically equal to the force acting perpendicular to the surface per unit area of \u200b\u200bthe given surface. Therefore, in order to determine the pressure at a certain point on the surface, the normal component of the force applied to the surface is divided by the area of \u200b\u200bthe small surface element on which this force acts. And in order to determine the average pressure over the entire area, the normal component of the force acting on the surface must be divided by the total area of \u200b\u200bthis surface.
Pascal (Pa)
The pressure is measured in SI system in pascals (Pa). This unit of pressure measurement got its name in honor of the French mathematician, physicist and writer Blaise Pascal, the author of the fundamental law of hydrostatics - Pascal's Law, which states that pressure exerted on a liquid or gas is transmitted to any point without changes in all directions. For the first time the unit of pressure "pascal" was introduced into circulation in France in 1961, according to the decree on units, three centuries after the death of the scientist.
One pascal equals the pressure caused by a force of one newton, evenly distributed and directed perpendicular to a surface of one square meter.
In pascals, not only the mechanical pressure (mechanical stress) is measured, but also the elastic modulus, Young's modulus, bulk modulus, yield point, proportional limit, tensile strength, shear resistance, sound pressure and osmotic pressure. Traditionally, it is in Pascals that the most important mechanical characteristics of materials in a resist material are expressed.
Technical atmosphere (at), physical (atm), kilogram-force per square centimeter (kgf / cm2)
In addition to the pascal, other (non-systemic) units are also used to measure pressure. One of these units is "atmosphere" (at). The pressure in one atmosphere is approximately equal to the atmospheric pressure on the Earth's surface at the level of the World Ocean. Today, "atmosphere" is understood as a technical atmosphere (at).
The technical atmosphere (at) is the pressure produced by one kilogram-force (kgf), evenly distributed over an area of \u200b\u200bone square centimeter. And one kilogram-force, in turn, is equal to the force of gravity acting on a body with a mass of one kilogram under acceleration conditions free fallequal to 9.80665 m / s2. One kilogram-force is thus equal to 9.80665 newtons, and 1 atmosphere is exactly equal to 98066.5 Pa. 1 at \u003d 98066.5 Pa.
In atmospheres, for example, the pressure in car tires is measured, for example, the recommended pressure in the tires of the passenger bus GAZ-2217 is 3 atmospheres.
There is also a "physical atmosphere" (atm), defined as the pressure of a mercury column with a height of 760 mm at its base, while the density of mercury is 13,595.04 kg / m3, at a temperature of 0 ° C and under conditions of gravitational acceleration equal to 9, 80665 m / s2. So it turns out that 1 atm \u003d 1.033233 at \u003d 101 325 Pa.
As for the kilogram-force per square centimeter (kgf / cm2), this non-systemic unit of pressure equals with good accuracy the normal atmospheric pressure, which is sometimes convenient for assessing various effects.
Bar (bar), barium
The off-system unit "bar" is equal to approximately one atmosphere, but is more accurate - exactly 100,000 Pa. In the SGS system, 1 bar is equal to 1,000,000 dyne / cm2. Previously, the name "bar" was carried by the unit now called "barium" and equal to 0.1 Pa or in the CGS system 1 barium \u003d 1 dyn / cm2. The words "bar", "barium" and "barometer" come from the same Greek word for "heaviness."
The mbar (millibar) unit of 0.001 bar is often used to measure atmospheric pressure in meteorology. And to measure pressure on planets where the atmosphere is very rarefied - μbar (microbar), equal to 0.000001 bar. On technical manometers, the scale is most often graduated in bars.
Millimeter of mercury (mmHg), millimeter of water (mmHg)
The off-system unit of measurement "millimeter of mercury" is equal to 101325/760 \u003d 133.3223684 Pa. It is designated "mm Hg", but sometimes it is designated "torr" - in honor of the Italian physicist, student of Galileo, Evangelista Torricelli, the author of the concept of atmospheric pressure.
The unit was formed in connection with a convenient way of measuring atmospheric pressure with a barometer, in which the mercury column is in equilibrium under the influence of atmospheric pressure. Mercury has a high density of about 13,600 kg / m3 and has a low pressure saturated steam at room temperature, therefore mercury was chosen for barometers at one time.
At sea level, the atmospheric pressure is approximately 760 mm Hg, and it is this value that is now considered to be the normal atmospheric pressure equal to 101325 Pa or one physical atmosphere, 1 atm. That is, 1 millimeter of mercury is equal to 101325/760 pascal.
Pressure is measured in millimeters of mercury in medicine, meteorology, and aviation navigation. In medicine, blood pressure is measured in mmHg, in vacuum technology, pressure gauges are graduated in mmHg, along with bars. Sometimes they even just write 25 microns, implying microns of mercury, when it comes to evacuation, and pressure measurements are carried out with vacuum gauges.
In some cases, millimeters of water are used, and then 13.59 mm Hg \u003d 1 mm Hg. Sometimes it is more expedient and convenient. A millimeter of a water column, like a millimeter of a mercury column, is an off-system unit, equal in turn to the hydrostatic pressure of 1 mm of a water column, which this column exerts on a flat base at a water column temperature of 4 ° C.
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The problem of arterial hypertension has become one of the most urgent in modern medicine. A large number of people suffer from high blood pressure (BP). Heart attack, stroke, blindness, kidney failure - all these are formidable complications of hypertension, the result of improper treatment or its absence at all. There is only one way to avoid dangerous complications - maintaining a constant normal blood pressure level with the help of modern high-quality drugs.
The selection of drugs is a doctor's business. The patient is required to understand the need for treatment, adherence to the doctor's recommendations and, most importantly, constant self-control.
Every patient suffering from hypertension should regularly measure and record their blood pressure, keep a diary of well-being. This will help the doctor assess the effectiveness of treatment, adequately select the dose of the drug, assess the risk of possible complications and effectively prevent them.
At the same time, it is important to measure blood pressure and know its average daily level at home, because pressure figures obtained at a doctor's appointment are often overestimated: the patient is worried, tired, sitting in a queue, forgot to take the medicine, and for many other reasons. And, on the contrary, at home situations may arise that cause a sharp increase in pressure: stress, physical activity, and more.
Therefore, every hypertensive person should be able to measure blood pressure at home in a calm, familiar environment in order to have an idea of \u200b\u200bthe true level of pressure.
HOW TO MEASURE PRESSURE CORRECTLY?
When measuring blood pressure, you must adhere to some rules:
Measure blood pressure in a calm atmosphere at a comfortable temperature, not earlier than 1 - 2 hours after eating, not earlier than 1 hour after smoking, drinking coffee. Sit comfortably against the back of a chair without crossing your legs. The arm should be bare, and the rest of the clothing should not be tight, tight. Do not talk, this may affect the correctness of the blood pressure measurement.
The cuff should be of the correct length and width for the arm. If the shoulder circumference exceeds 32 cm or the shoulder has a tapered shape, which makes it difficult to correctly apply the cuff, a special cuff is required. the use of a narrow or short cuff leads to a significant overestimation of the BP figures.
Apply the cuff so that its bottom edge is 2.5 cm above the edge of the cubital fossa. Do not squeeze it too tight - a finger should pass freely between the shoulder and the cuff. Place the stethoscope where you can best listen for the pulsation of the brachial artery just above the cubital fossa. The membrane of the stethoscope should fit snugly against the skin. But do not press too hard to avoid additional compression of the brachial artery. The stethoscope should not touch the tonometer tubes so that the sounds from contact with them do not interfere with the measurement.
Place the stethoscope at the level of the patient's heart or at the level of his 4th rib. Pump air vigorously into the cuff, slow inflation will increase pain and impair the quality of sound perception. Release air from the cuff slowly - 2 mmHg. Art. per second; the slower the air release, the better the measurement quality.
Re-measurement of blood pressure is possible in 1 - 2 minutes after the complete release of air from the cuff. BP can fluctuate from minute to minute, so the average of two or more measurements more accurately reflects the true intra-arterial pressure. SYSTOLIC AND DIASTOLIC PRESSURE
To determine the pressure parameters, it is necessary to correctly assess the sounds that are heard “in the stethoscope”.
Systolic pressure is determined by the closest division of the scale, at which the first successive tones are heard. With pronounced rhythm disturbances, for accuracy, it is necessary to make several measurements in a row.
Diastolic pressure is determined either by a sharp decrease in the volume of tones, or by their complete cessation. Zero pressure effect, i.e. continuous to 0 tones, can be observed in some pathological conditions (thyrotoxicosis, heart defects), pregnancy, in children. With a diastolic pressure above 90 mm Hg. Art. it is necessary to continue measuring blood pressure for another 40 mm Hg. Art. after the disappearance of the last tone, in order to avoid falsely high values \u200b\u200bof diastolic pressure due to the phenomena of "auscultatory failure" - a temporary cessation of tones.
Often, to obtain a more accurate result, it is necessary to measure the pressure several times in a row, and sometimes calculate the average value, which more accurately corresponds to the true intra-arterial pressure.
HOW TO MEASURE PRESSURE?
To measure blood pressure, doctors and patients use different types of blood pressure monitors. Tonometers are distinguished on several grounds:
By the location of the cuff: tonometers “on the shoulder” are in the lead - the cuff is applied to the shoulder. This cuff position provides the most accurate measurement result. Numerous studies have shown that all other positions (“wrist cuff”, “finger cuff”) can give significant discrepancies with true pressure. The measurement result with a wrist device is highly dependent on the position of the cuff relative to the heart at the time of measurement and, most importantly, on the measurement algorithm used in a particular device. When using digital blood pressure monitors, the result may even depend on the temperature of the finger and other parameters. Such blood pressure monitors cannot be recommended for use.
Pointer or digital - depending on the type of determination of measurement results. The digital tonometer has a small screen on which the pulse, pressure and some other parameters are displayed. A dial tonometer has a dial and an arrow, and the researcher fixes the measurement result.
The tonometer can be mechanical, semi-automatic or fully automatic, depending on the type of air injection device and the measurement method. WHICH TONOMETER TO CHOOSE?
Each tonometer has its own characteristics, advantages and disadvantages. Therefore, if you decide to buy a tonometer, pay attention to the features of each of them.
Cuff: Should be the same size as your arm. The standard cuff is designed for arms with a circumference of 22 - 32 cm. If you have a large arm, you need to purchase a larger cuff. To measure pressure in children, there are small baby cuffs. In special cases (birth defects), cuffs are required to measure pressure at the thigh.
It is better if the cuff is made of nylon, equipped with a metal ring, which greatly facilitates the process of attaching the cuff to the shoulder when measuring pressure yourself. The inner chamber should be seamless or specially shaped to provide strength to the cuff and make measurement more comfortable.
Phonendoscope: Usually a phonendoscope comes with a tonometer. Pay attention to its quality. For home blood pressure measurement, it is convenient when the tonometer is equipped with a built-in phonendoscope. This is a great convenience, since in this case the phonendoscope does not need to be held in hand. In addition, there is no need to worry about the correctness of its location, which can be a serious problem in case of independent measurement and lack of sufficient experience.
Manometer: a manometer for a mechanical tonometer should have bright clear divisions, sometimes they are even luminous, which is convenient when measuring in a dark room or at night. It is better if the gauge is equipped with a metal case, this gauge is more durable.
It is very convenient when the pressure gauge is combined with a pear - an air injection element. This facilitates the process of measuring pressure, allows the manometer to be correctly positioned relative to the patient, and increases the accuracy of the result.
Pear: as mentioned above, it is good if the pear is combined with a pressure gauge. A quality pear is equipped with a metal screw. In addition, if you are left-handed, note that there are pears adapted to work with the right or left hand.
Display: When choosing a tonometer, the size of the display matters. There are small displays where only one parameter is displayed - for example, the last blood pressure measurement. On the large display you can see the result of blood pressure and pulse measurements, a color pressure scale, the average pressure value from the last several measurements, an arrhythmia indicator, and a battery charge indicator.
Additional functions: the automatic blood pressure monitor can be equipped with such convenient functions as:
arrhythmia indicator - if the heart rhythm is disturbed, you will see a mark on the display or hear a beep. The presence of arrhythmia distorts the correctness of blood pressure determination, especially with a single measurement. In this case, it is recommended to measure the pressure several times and determine the average value. Special algorithms of some devices allow accurate measurements, despite rhythm disturbances;
memory for the last few measurements. Depending on the type of tonometer, it may have the function of storing several last measurements from 1 to 90. You can view your data, find out the last pressure figures, draw up a pressure graph, calculate the average value;
automatic calculation of average pressure; sound notification;
function of accelerated pressure measurement without loss of measurement accuracy; there are family models, in which separate function buttons provide the ability to independently use the tonometer by two people, with a separate memory for the last measurements;
convenient models that provide the ability to work both from batteries and from a common electrical network. At home, this not only increases the convenience of measurement, but also reduces the cost of using the device;
there are models of tonometers equipped with a printer for printing the latest blood pressure readings from memory, as well as devices that are compatible with a computer.
Thus, a mechanical tonometer provides a higher quality measurement in experienced hands, in a researcher with good hearing and vision, able to correctly and accurately follow all the rules for measuring blood pressure. In addition, a mechanical tonometer is significantly cheaper.
An electronic (automatic or semi-automatic) tonometer is good for home blood pressure measurement and can be recommended for people who do not have the skills to measure blood pressure by auscultation method, as well as for patients with reduced hearing, vision, and reaction. does not require the measuring person to participate directly in the measurement. One cannot but appreciate the usefulness of such functions as automatic air pumping, accelerated measurement, memory of measurement results, calculation of average blood pressure, arrhythmia indicator and special cuffs that exclude painful sensations during measurement.
However, the accuracy of electronic blood pressure monitors is not always the same. The preference should be given to clinically approved devices, that is, those that have been tested according to world-famous protocols (BHS, AAMI, International Protocol).
Sources The magazine “CONSUMER. Expertise and Tests ", 38'2004, Maria Sasonko apteka.potrebitel.ru/data/7/67/54.shtml
