Caused by the weight of air. 1 m³ of air weighs 1.033 kg. For every meter of the earth's surface there is an air pressure of 10033 kg. This refers to a column of air from sea level to the upper atmosphere. If we compare it with a column of water, the diameter of the latter would have a height of only 10 meters. That is, atmospheric pressure is created by its own air mass. The amount of atmospheric pressure per unit area corresponds to the mass of the air column located above it. As a result of an increase in air in this column, pressure increases, and as air decreases, a decrease occurs. Normal atmospheric pressure is considered to be air pressure at t 0°C at sea level at a latitude of 45°. In this case, the atmosphere presses with a force of 1.033 kg for every 1 cm² of earth's area. The mass of this air is balanced by a column of mercury 760 mm high. Atmospheric pressure is measured using this relationship. It is measured in millimeters of mercury or millibars (mb), as well as in hectopascals. 1mb = 0.75 mm Hg, 1 hPa = 1 mm.
Measuring atmospheric pressure.
measured using barometers. They come in two types.
1. A mercury barometer is a glass tube, which is sealed at the top, and the open end is immersed in a metal bowl with mercury. A scale indicating the change in pressure is attached next to the tube. The mercury is acted upon by air pressure, which balances the column of mercury in the glass tube with its weight. The height of the mercury column changes with pressure changes.
2. A metal barometer or aneroid is a corrugated metal box that is hermetically sealed. Inside this box there is rarefied air. The change in pressure causes the walls of the box to vibrate, pushing in or out. These vibrations by a system of levers cause the arrow to move along a graduated scale.
Recording barometers or barographs are designed to record changes atmospheric pressure. The pen picks up the vibration of the walls of the aneroid box and draws a line on the tape of the drum, which rotates around its axis.
What is atmospheric pressure?
Atmospheric pressure on the globe varies widely. Its minimum value - 641.3 mm Hg or 854 mb was recorded over the Pacific Ocean in Hurricane Nancy, and the maximum - 815.85 mm Hg. or 1087 MB in Turukhansk in winter.
Air pressure on the earth's surface changes with altitude. Average atmospheric pressure value above sea level - 1013 mb or 760 mm Hg. The higher the altitude, the lower the atmospheric pressure, as the air becomes more and more rarefied. In the lower layer of the troposphere to a height of 10 m it decreases by 1 mmHg. for every 10 m or 1 mb for every 8 meters. At an altitude of 5 km it is 2 times less, at 15 km - 8 times, 20 km - 18 times.
Due to air movement, temperature changes, seasonal changes Atmosphere pressure constantly changing. Twice a day, in the morning and in the evening, it increases and decreases the same number of times, after midnight and after noon. During the year, due to the cold and compacted air, atmospheric pressure is at its maximum in winter and at its minimum in summer.
Constantly changing and distributed across the earth's surface zonally. This occurs due to uneven heating of the earth's surface by the Sun. The change in pressure is affected by the movement of air. Where there is more air, the pressure is high, and where the air leaves - low. The air, having warmed up from the surface, rises and the pressure on the surface decreases. At altitude, the air begins to cool, becomes denser and sinks to nearby cold areas. Atmospheric pressure increases there. Consequently, the change in pressure is caused by the movement of air as a result of its heating and cooling from the earth's surface.
Atmospheric pressure in the equatorial zone constantly reduced, and in tropical latitudes - increased. This occurs due to constantly high air temperatures at the equator. The heated air rises and moves towards the tropics. In the Arctic and Antarctic, the surface of the earth is always cold and the atmospheric pressure is high. It is caused by air that comes from temperate latitudes. In turn, in temperate latitudes, due to the outflow of air, a zone of low pressure is formed. Thus, there are two belts on Earth atmospheric pressure- low and high. Decreased at the equator and in two temperate latitudes. Raised on two tropical and two polar. They may shift slightly depending on the time of year following the Sun towards the summer hemisphere.
Polar high pressure belts exist all year round, however, in summer they contract and in winter, on the contrary, they expand. All year round, areas of low pressure persist near the Equator and in the southern hemisphere in temperate latitudes. In the northern hemisphere, things happen differently. In the temperate latitudes of the northern hemisphere, the pressure over the continents increases greatly and the low pressure field seems to be “broken”: it persists only over the oceans in the form of closed areas low atmospheric pressure- Icelandic and Aleutian minimums. Over the continents, where the pressure has noticeably increased, winter maximums form: Asian (Siberian) and North American (Canadian). In summer, the low pressure field in the temperate latitudes of the northern hemisphere is restored. At the same time, a vast area of low pressure is formed over Asia. This is the Asian low.
In the belt increased atmospheric pressure- in the tropics - the continents heat up more than the oceans and the pressure above them is lower. Because of this, subtropical highs are distinguished over the oceans:
- North Atlantic (Azores);
- South Atlantic;
- South Pacific;
- Indian.
Despite large-scale seasonal changes in its performance, belts of low and high atmospheric pressure of the Earth- formations are quite stable.
Physics explains pressure as a force that acts on a unit surface area. When two identical forces act on different surfaces, the larger force will be the one acting on the smaller area. The blade of a sharp knife, when pressed on a vegetable, will cut it, but under the influence of a blunt object, the vegetable will remain intact.
In contact with
Determination of atmospheric pressure
This definition refers to the effect of air on a certain place, namely: a column of air on the surface. Its changes have an impact on weather conditions and air temperature, as well as on the health of people and animals. Too low of a level leads to physical and mental discomfort, and if the body is weakened, to serious illnesses and death.
Atmospheric pressure decreases with increasing altitude. Therefore, in airplane cabins, a level is specially maintained above that which is overboard. People and animals living in mountainous areas adapt to such conditions, but travelers should take every precaution to avoid developing altitude sickness.
Non-system unit of measure
The atmosphere is considered a non-systemic unit of measurement. One atmosphere corresponds to the pressure at sea level. There are two types of this unit of measurement:
- physical (normal or standard) atmosphere, short for which is atm;
- technical - at.
This value is used to measure the uniform perpendicular effect of force on a flat surface. One standard atmosphere is the pressure of a column of mercury, the height of which is 760 millimeters, at zero temperature and a density of mercury equal to 13,595.04 kilograms per cubic meter.
The prefixes “ata” and “ati” were previously used to denote absolute and excess indicators. In the case when the atmospheric pressure is less than absolute, the difference was calculated, which is the excess. Rarefaction, or vacuum, is the difference that is calculated when the level of atmospheric pressure is higher than the absolute value.
General information about pascals
A quantity such as pascal is used to measure atmospheric force, the action of which extends strictly perpendicularly to a unit surface. A force of one newton over an area of one square meter is equal to one pascal. These numbers indicate a fairly low atmospheric pressure, so the resulting measurements are reported in megapascals (MPa) or kilopascals (kPa).
different areas of activity are measured in different quantities. For example, when measuring it in cars, the following values may be indicated:- atmosphere;
- bars;
- pounds per square inch;
- megapascals;
- kilogram of force per square centimeter - technical atmosphere.
Pascal belongs to the International System of Units (SI) and is also used to measure elastic moduli, yield strength, mechanical stress, fugacity, proportionality limit, osmotic and sound pressure, tensile and shear strength, Young's modulus.
The dimensions of the units of measurement of this quantity and energy are the same, but they describe different physical properties of objects, and therefore cannot be considered equivalent. Therefore, pascals are not used as a unit of energy density, and pressure is not measured in joules.
General rules of the International System of Units It has been established that the name of the pascal unit is written with a lowercase letter, and its designation with a capital letter. This rule holds true when writing other units of measurement formed using pascal. This quantity first became known in France in 1961 thanks to the mathematician and physicist Blaise Pascal, after whom it was named.
Megapascals
Megapascal is a unit of measurement of the atmospheric column that is a multiple of pascal. In order to convert megapascals into atmospheres, special calculators are most often used, many of which work online.
One megapascal is one thousand kilopascals, which in turn is one million pascals. How many atmospheres are then contained in a megapascal? If we accurately translate these values, then one megapascal is 10.197 atm and 9.8692 atm - technical and physical atmospheres, respectively.
When solving physical problems, accurate calculations are rarely carried out, therefore the standard 1 atmosphere in megapascals is taken as 0.1 MPa, and the physical one as 0.987 MPa (when calculated back, 1 MPa is 10 technical atmospheres and 9.87 physical). At the same time, one millimeter of water column is equal to about 10 Pa, and one mercury column is 133 Pa. The normal value - 760 millimeters of mercury - is equal to 101,325 pascals or 101 kilopascals.
Concepts such as bar and atmosphere are familiar to every real owner, because it is in these quantities that any pressure is measured: water in a tap/system, air in car wheels, etc. However, not everyone can accurately answer how many atmospheres 1 bar contains, since quite often these values are simply equated, attributing the difference between them to an error. But is this right? Let's figure it out.
What is the bar and atmosphere like?
Bar is a word of Greek origin that literally translates as “heaviness.” In science, this word refers to 2 units at once:
- the first is the generally accepted unit of measurement of pressure in the physical system of units GHS (CentimeterGramSecond);
- the second is the extra-system meteorological one, also called the standard atmosphere.
In the first case, 1 bar = 1 dyne/cm2, where 1 dyne is a unit of force.
In the second, 1 bar (standard atmosphere) = 1*ֹ10 6 dynes/cm 2 (bar from GHS).
The atmosphere is also a unit of measurement of pressure with a double meaning:
- in the first case (it is called standard, normal and physical and denoted “atm”) it is equal to the atmospheric pressure present at sea level at zero temperature and normal acceleration of gravity, we will not overload you with unnecessary numbers, let’s just say that it is equal to 101325 Pa;
- in the second case (when the atmosphere is called technical and designated “at”) it is equal to the pressure produced by a force of 1 kgf on a perpendicular surface with an area of 1 cm 2. In Pascals (Pa) it is 98066.5. As you can see, the difference between them is noticeable, although not too significant - a little more than 3%.
For reference.
- 1 kgf (kilogram-force) is a generally accepted (along with second and meter) unit of force, equal to the force imparted to a kilogram at rest by the acceleration of gravity.
- 1 Pa is a unit of measurement of pressure equal to the force that is uniformly imparted to a surface of 1 m2 area by a force equal to 1 N.
- 1 dyne/cm2 = 0.1 Pa.
- 1 N = 1 kg m/s 2 = 10 5 dyn.
Because of such a variety of definitions, all the confusion occurs, so as not to understand which people came up with to round 1 bar = 1 atmosphere. But in fact, everything is extremely simple.
So, 1 bar is how many atmospheres?
In meteorology, 1 bar = 0.98692 atm, in all other areas 1 bar = 1.0197 atm.
Therefore, to convert bars to atmospheres, simply divide the given number of bars by 0.98692 (or 1.0197, if we are talking about meteorology)
For example, you have a pressure of 5 bar, in atmospheres this is 5/0.98692 = 5.066 at.
For normal atmospheric pressure, it is customary to take the air pressure at sea level at a latitude of 45 degrees at a temperature of 0°C. Under these ideal conditions, the column of air presses on each area with the same force as a column of mercury 760 mm high. This figure is an indicator of normal atmospheric pressure.
Atmospheric pressure depends on the altitude of the area above sea level. At higher elevations, the indicators may differ from ideal, but they will also be considered the norm.
Atmospheric pressure standards in different regions
As altitude increases, atmospheric pressure decreases. So, at an altitude of five kilometers, pressure indicators will be approximately two times less than below.Due to the location of Moscow on a hill, the normal pressure level here is considered to be 747-748 mm column. In St. Petersburg, normal pressure is 753-755 mm Hg. This difference is explained by the fact that the city on the Neva is located lower than Moscow. In some areas of St. Petersburg you can find a pressure norm of an ideal 760 mm Hg. For Vladivostok, normal pressure is 761 mmHg. And in the mountains of Tibet – 413 mmHg.
Impact of atmospheric pressure on people
A person gets used to everything. Even if normal pressure readings are low compared to the ideal 760 mmHg, but are the norm for the area, people will.A person’s well-being is affected by sharp fluctuations in atmospheric pressure, i.e. decrease or increase in pressure by at least 1 mmHg within three hours
When pressure decreases, a lack of oxygen occurs in a person’s blood, hypoxia of body cells develops, and the heartbeat increases. Headaches appear. There are difficulties with the respiratory system. Due to poor blood supply, a person may experience pain in the joints and numbness in the fingers.
Increased pressure leads to an excess of oxygen in the blood and tissues of the body. The tone of blood vessels increases, which leads to their spasms. As a result, the body's blood circulation is disrupted. Visual disturbances may occur in the form of spots before the eyes, dizziness, and nausea. A sharp increase in pressure to large values can lead to rupture of the eardrum.
In order to find out how many atmospheres there are in a pascal, you need to use a simple online calculator. Enter in the left field the number of pascals you want to convert. In the field on the right you will see the result of the calculation. If you need to convert pascals or atmospheres to other units of measurement, simply click on the appropriate link.
The SI unit of measurement is the pascal (Pa, Pa), equal to the pressure when a force of 1 newton is uniformly applied to a flat surface with an area of 1 square meter.
m. Mechanical stress, elastic moduli, Young's modulus, yield strength, proportionality limit, tensile and shear strength, sound and osmotic pressure, volatility are also measured in pascals. The unit was named after the French physicist and mathematician Blaise Pascal in 1961.
What is "atmosphere"
An off-system unit of pressure that approximates atmospheric pressure at ocean level.
There are equally two units - the technical atmosphere (at, at) and the normal, standard or physical atmosphere (atm, atm). One technical atmosphere is a uniform perpendicular pressure of a force of 1 kgf on a flat surface with an area of 1 cm².
1 at = 98,066.5 Pa.
How to convert pressure to Pascals
The standard atmosphere is a pressure of a mercury column with a height of 760 mm at a mercury density of 13,595.04 kg/m³ and zero temperature. 1 atm = 101,325 Pa = 1.033233 at. In the Russian Federation, only the technical atmosphere is used.
In the past, the terms "ata" and "ati" were used for absolute and gauge pressure.
Excess pressure is the difference between absolute and atmospheric pressure, when absolute pressure is greater than atmospheric pressure. The difference between atmospheric and absolute pressure, when absolute pressure is lower than atmospheric pressure, is called rarefaction (vacuum).
Atmosphere pressure
Pascal(Russian designation: Pa, international: Pa) is a unit of pressure (mechanical stress) in the International System of Units (SI).
Pascal is equal to the pressure caused by a force equal to one newton, uniformly distributed over a surface normal to it with an area of one square meter: 1 Pa = 1 N m−2.
Atmospheric pressure: conversion of megapascals (MPa) to atmospheres
Pascal is related to SI base units as follows: 1 Pa = 1 kg m−1 s−2.
In SI, the pascal is also a unit of measurement for mechanical stress, elastic modulus, Young's modulus, bulk modulus, yield strength, proportional limit, tensile strength, shear strength, sound pressure, osmotic pressure, volatility (fugacity).
In accordance with the general SI rules regarding derived units named after scientists, the name of the unit pascal is written with a lowercase letter, and its designation is written with a capital letter.
This spelling of the notation is also preserved in the notation of other derived units formed using pascal. For example, the unit of dynamic viscosity is written as Pa s.
The unit is named after the French physicist and mathematician Blaise Pascal. The name was first introduced in France by the decree on units in 1961.
Decimal multiples and submultiples are formed using standard SI prefixes.
In practice, approximate values are used: 1 atm = 0.1 MPa and 1 MPa = 10 atm. 1 mm of water column is approximately equal to 10 Pa, 1 mm of mercury is approximately equal to 133 Pa.
Normal atmospheric pressure is considered to be 760 mmHg, or 101,325 Pa (101 kPa).
The dimension of the pressure unit (N/m²) coincides with the dimension of the energy density unit (J/m³), but from the point of view of physics, these units are not equivalent, since they describe different physical properties.
In this regard, it is incorrect to use Pascals to measure energy density, and write pressure as J/m³.
How much atmosphere is in 1 bar?
The name of the unit of pressure, bar, comes from the Greek word for weight. A derivative of this unit, the millibar, is widely used in meteorology.
The bar belongs to the category of units defined by the forces of force and area. There are two units with the same name, called a line. One of them is the unit of measurement of pressure adopted in the physical system of units CGS (centimeter, gram, other). This unit is defined as 1 dyne/cm2, where 1 dyne is the unit of force used in the system.
In addition, below 1 bar is the non-systemic system, a meteorological unit, also called the standard atmosphere. The ratio between the two bands is 1 bar or 1 standard atmosphere is 106 dyne/cm2.
In addition to the standard atmosphere, the technical (metric) atmosphere and the physical (normal) atmosphere are used in practice. Technical or metric atmosphere is used in the technical system of the MKGSS units. It is also denoted as kgf/cm2. The technical atmosphere is defined as the pressure created by a force of 1 kgf, directed perpendicularly and uniformly distributed over a flat surface of 1 cm2.
The ratio of the rod to the technical atmosphere is 1 bar = 10197 kgf/cm2.
The normal atmosphere is an additional system unit, the same pressure on the surface of the Earth. It is defined as a pressure controlled by 760 mm of mercury at 0 degrees Celsius, normal density of mercury and normal weight acceleration. The connection between the strip and the normal or physical atmosphere is 1 bar = 0.98692 atm.
Often, quick and convenient calculations do not require high accuracy. Therefore, the above values may be rounded depending on how much error you are willing to accept in the measurements.
Atmospheric normal and standard pressure
If the error is 0.5%, you can take 1 bar, which is equal to 0.98 atm. or 1.02 kgf/cm2. If we ignore the difference between the technical atmosphere and the bar (standard atmosphere), then the error is 2%.
And by allowing an error of 3%, we can take into account the physical and standard atmosphere, which are equivalent to each other.
Based on materials from the site http://otvet.mail.ru
