Absolute pressure in nature and technology

Pressure is a quantity from physics that shows the numerical value of the ratio of the force acting on the received unit of a certain surface. It is assumed that the direction of this force is strictly perpendicular to the surface area. If in the SI system, which is adopted in the territory of the CIS countries, the force is Newton or kilogram-force, and the area is square centimeters (millimeters, meters), then we get:

P = F / S = H / cm2 = Pa

Pascal is one of the varieties of quantities (used in engineering and physics). As a rule, the values are indicated in MPa - MegaPascal. This is convenient for reducing the number of zeros. The term "atmosphere" is often used in engineering and everyday life. Absolute pressure, as well as relative pressure, can be measured in "atmospheres", Pa, and other units.

In practice, the term "atmosphere" also has several concepts: standard and technical. The standard, physical or normal atmosphere is designated "atm" (ata) and the standard value is 101325 Pa, which means the mercury column pressure at sea level and at 0 degrees Celsius. You can also find the expression 760 mm.rt.s. (Mm Hg). The technical atmosphere has nothing to do with the term absolute pressure, since it has a different definition and units of measurement "at" (ati). The definition reads: "Force perpendicularly acting on the mass (1 kg) with the acceleration of gravity (1g) uniformly per unit surface area (1 cm2)".

There are also definitions:

Absolute pressure - measured pressure relative to absolute zero - vacuum (ata).

Relative pressure is the measured pressure relative to the standard atmosphere (ati).

Excessive pressure - can both be equal to the relative, and be its difference (ati).

Very often the concepts of absolute and excess pressure are singled out as two single types. In fact, there is no significant difference in the excess and relative pressure. This is more speech speed, which is more customary to use specialists of this or that branch.

Let's return to the concept of absolute pressure. As already mentioned, it has an absolute value, i.е. Measured from physical zero. It's like a scale on a ruler - you measure from 0 and how much you need. In nature, this concept is rarely resorted to in calculations, because "overboard" is always already some kind of pressure. Therefore, it is more convenient to measure from it. For example, the pressure in the tires of your auto master at the SRT tells you in the atmosphere (for cars about 2.2 atm). Cylinders also have a unit of measurement - the atmosphere, but already technical. This is due to the fact that the use of the difference is important.

Separately, it should be noted that the air pressure with altitude, of course, varies. The absolute and relative pressure changes with each kilometer. To determine it, all external factors should be taken into account: temperature, density and acceleration of gravity. These data are standard for each height. They are summarized in the table of pressure distribution by altitude or can be represented in the form of graphs. This information is useful mainly to aircraft designers (aircraft). Since the aircraft has a range of working heights from 0 to 12 km (passenger). And, therefore, all systems, units and operation of aircraft engines must be designed taking into account different external conditions.

In the world, different values are used, which measure both excess and absolute pressure. It all depends on the geographical region and area of application. Below is a chain of basic units of pressure measurement:

1 Pa = 9.87 * 10-6 atm. = 1.02 at. = 1,02 kg / cm2 = 10-5 Bar = 1,45 * 10-4 PSI =

= 7.5 * 10-3 mm Hg. = 0.120 mm.water.st

As can be seen, the range of pressure units is quite large. From this list in the CIS countries the most frequent are Pa, atm., At., Kg / cm2, mm Hg.

Among other things, in nature and processes there is static and total pressure. Static pressure is the pressure that is measured from the flow of the working fluid (ie its natural pressure). The total pressure (inhibited pressure) is the pressure measured directly in the flow (ie, when the flow is braking the sensor).

Pressure affects a person more than temperature, because the temperature of the human body has some reserve, and the pressure - very small. That is why the elderly and sick people react very sensitively to the change in pressure. For technical needs, pressure gauges are used - manometers, for hydrometeorological services - barometers.