Meteorological pressure

1, the pressure generated by the movement of air molecules on any surface unit area. p=F/S

2. Air pressure is the atmospheric pressure acting on the unit area, which is equal to the weight of the vertical air column extending upward to the upper limit of the atmosphere on the unit area. Air pressure is expressed in hectopascals, with one decimal place reserved.

SI unit: Pascal, abbreviated as Pa, with the symbol of PA.

Common unit: standard atmospheric pressure.

A unit of air pressure, usually the height of a mercury column. For example, a standard atmospheric pressure is equal to the weight of a 760mm high mercury column, which is equivalent to bearing an atmospheric pressure of 1.0336kg in an area of one square centimeter. Because the weight and length units used in different countries are different, and the pressure units are not uniform, it is not convenient to compare and analyze the global pressure. Therefore, "hectopascals" are used as the air pressure unit in the world. After conversion:

A standard atmospheric pressure = 10 13 hectopascals (millibars)

1 mm Hg height = 4/3 hectopascals (millibars)

1 hectopascal (millibar) = = 75 mm Hg height.

[Edit this paragraph] Reason

According to the theory of molecular dynamics, the pressure of gas is caused by the frequent collision of a large number of molecules with the container wall. The collision time of a single molecule on the container wall is very short, and the effect is discontinuous. When a large number of molecules collide with the container wall frequently, the force acting on the container wall is continuous and uniform, and the ratio of this pressure to the container wall area is the pressure.

[Edit this paragraph] Calculation method

There are usually equilibrium condition method and Newton's law of motion method.

The formula is only a rough calculation, and sometimes the measured value is inaccurate, so everything should be based on reality.

1. After Torricelli measured the air pressure, people used the formula P = f/s to calculate the mass of air per unit area, then applied the density of air to calculate the volume, and then divided by the mass, we knew the distance from the ground to the top of the atmosphere.

2. It is known that when the volume of gas, the amount of substance and the absolute temperature (where R is a constant, R = 8.314 Pa m 3/mol k or R = 0.0814 ATM l/mol k), the gas pressure can be obtained by the formula PV=nRT. This formula also has deformation formulas pV=mRT/M and p = ρ rt/m.

[Edit this paragraph] Factors affecting stress

Atmospheric pressure is related to altitude, atmospheric temperature and atmospheric density, and generally decreases exponentially with altitude. The air pressure changes every day and every year. In a year, the air pressure in winter is higher than that in summer. In a day, the air pressure has a maximum value and a minimum value, which appear at 9 ~ 10 and 15 ~ 16 respectively, and the second high value and the second low value appear at 2 1 ~ 22 and 3 ~ 4 respectively. The daily variation of air pressure is small, generally 0. 1 ~ 0.4 kPa, and decreases with the increase of latitude. The change of air pressure is closely related to wind and weather, so it is an important meteorological factor. The commonly used units of air pressure are Pa, mmHg and millibar. The conversion relationship between them is:100pa =1mbar ≈ 3/4 mm mercury column height. Commonly used instruments for measuring atmospheric pressure in meteorological observation include mercury barometer, empty box barometer and barometer. When the temperature is 0℃ and the pressure is 760mm, the standard atmospheric pressure is first measured by Italian scientist Torricelli.

Related words:

Barometer: An instrument for measuring air pressure. The most common ones are mercury barometer and empty box barometer. It is also a relatively accurate instrument. ...

Three centuries ago, an experiment was carried out in the German city of Madeborg. Otto Gehrick, the mayor who invented the air extractor, combined two hollow copper hemispheres with a diameter of 37 cm to seal them, and then used the air extractor to extract the air from the copper balls. Tie four strong horses to the rings in each hemisphere and pull them in opposite directions at the same time. These two hemispheres cannot be separated. Finally, 20 big horses were used, and the copper ball split in half with a loud noise.

This is a famous hemispheric experiment in Fort Madre. Experiments show that air not only has pressure, but also has great pressure. The average body surface area of an adult is 2 square meters, and the atmospheric pressure of his whole body is 200,000 Newton.

Air pressure is atmospheric pressure. Air has weight, and air pressure refers to the force exerted by the atmosphere per unit area. The so-called air pressure in a place refers to the total weight of the air column extending vertically upward to the top of the atmosphere per unit area of the place.

In meteorology, hectopascals are often used as the unit of pressure measurement. Specifically, the sea level pressure at 0℃ and latitude of 45 degrees is called 1 atmospheric pressure, and its value is 760 mm Hg, or equivalent to 10 13.25 hectopascals.