That is "atmospheric pressure", in any surface, entirely by air pressure generated by the weight of
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No. 2
Of Physics. Aerodynamic pressure that object. The size and height, temperature and other conditions related to the higher from the ground, the smaller the pressure, such as the air pressure at high altitude or on the mountain than the pressure on the small flat.
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No. 3
The "atmospheric pressure" (379).
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No. 4
Pressure (atmospheric pressure) In any unit area on the surface of the air pressure generated by molecular motion. Usually measured by a high degree of cross-sectional area of the units at or above the weight of said vertical atmospheric column. The size and pressure altitude, air temperature, atmospheric density, generally increasing with height exponential decrease. There are diurnal and annual air pressure changes. One year, the high pressure in winter than in summer. Day, pressure has a maximum value, a minimum value, respectively, in the 9 to 10 and 15 to 16, and a second high-value and a second low-value, respectively, in 21 to 22 am and 3 to 4 pm . A lesser extent on changes in air pressure, usually 0.1 to 0.4 kPa, and decreases with increasing latitude. Changes in air pressure and wind, the weather is good or bad and so close, so it is important meteorological factors. Commonly used pressure units Pa (pa), mm mercury column height (mm · hg), millibar (mb). Conversion between them as follows: 100 Pa = 1 mbar ≈ 3 / 4 mm Hg higher. Commonly used in meteorological observation instruments are measuring pressure mercury barometer, aneroid barometer, barometer. 101.325 kPa pressure (760 mm tribute column), called the standard atmospheric pressure, which is equivalent to the acceleration of gravity is 9.80665 m / sec 2, when the temperature is 0 ℃ vertical column of mercury 760 mm high pressure. Related words: Barometer: barometric pressure measurement instruments, the most common are the mercury barometer and the aneroid barometer two. In the three centuries ago, the German city of Magdeburg had publicly made an experiment, two 37 cm diameter hollow copper hemispheres together, so close does not leak, and then use the air pump inside the copper ball deprived of air. In each hemisphere of each ring to fasten the four strong horses pulling in the opposite direction at the same time, the two hemispheres can not be separated. Finally, the 20 in Malaysia, with a bang copper ball was split in two. This is the famous Magdeburg hemispheres experiment. The experiment shows that the air is not only stressful, but the pressure is still very great. An average adult body surface area of 2 square meters, his body suffered atmospheric pressure of 20 kN. Pressure is atmospheric pressure. Is the weight of air, atmospheric pressure is applied to the force per unit area. A place called the pressure, refers to the unit area of land extending vertically upward to the top of the atmosphere of the total weight of the air column. HPa pressure commonly used as a meteorological unit of measure. Specifically so provides: the temperature is 0 ℃, the latitude of 45 degrees when the sea level pressure as a standard, known as an atmospheric pressure, the high value of 760 mm Hg, or the equivalent of 1013.25 hPa.
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Definition
Definition of gas pressure 1, in any unit area on the surface of the air pressure generated by molecular motion. p = F / S 2, air pressure per unit area is the role of atmospheric pressure, that is equal to the unit area extends up to the upper atmosphere, the weight of the vertical air column. Air pressure in hPa (hPa) as a unit, take a decimal. International system of units: Pascal, referred to as Pa, symbol Pa. Common units: the standard atmospheric pressure. Said pressure unit, customarily used mercury column height. For example, a standard atmospheric pressure is equal to 760 millimeters of mercury higher weight, it is equivalent to one square centimeter area of 1.0336 kg weight to withstand the atmospheric pressure. As used by countries in different units of weight and length, and thus pressure unit is not uniform, this does not facilitate a comparative analysis of the global pressure. Therefore, international harmonization of regulations with the "hPa" as the pressure unit. After conversion: A standard atmospheric pressure = 1013 hPa (mbar) 1 millimeters of mercury (tribute column) column height = 4 / 3 hPa (mbar) 1 hPa (mbar) = 76mm of mercury (tribute column) the column height.
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Causes
From the molecular kinetic theory shows that the gas pressure is frequently a large number of molecular collisions arising from the container wall. Single molecule of the container wall collision time is very short, the role is not continuous, but a large number of molecular collisions frequently the wall, the force of the wall is a continuous, uniform, the pressure and the wall area ratio is the size of the pressure .
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Calculation
Usually there is a balance condition method and Newton's laws of motion method (Sometimes the formula is only a rough calculation and measured values are not allowed, all should be based on the actual date). 1, measured in the Torricelli out of the air, people by the formula p = F / S, calculated on a per unit area in the number of air quality. Then apply the density of the air, find the volume, then divided by the quality of the ground to know the distance to the top of the atmosphere. 2, is known: the gas volume, amount of substance, the absolute temperature, can find the formula PV = nRT gas pressure (where R is a constant, R = 8.314 Pamidronate 3 / mole K or R = 0.0814 atm L / Moore K). This formula also deformation formula pV = mRT / M, p = ρRT / M.
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Found that the great significance of air pressure
The atmosphere has weight, and to put pressure on us, this is a very simple and seem obvious phenomenon. However, people are feeling less than. Pressure has become a part of your life, so you are not aware of it. Scientists, too early, they never take into account the air and the atmosphere has weight. Torricelli's discovery is the formal study of weather and atmospheric start, let us begin to understand the atmosphere, the gravity of Newton and other scientists laid the foundation. This new discovery while Torricelli vacuum created the concept of the invention of the basic meteorological research instruments - barometer.
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The discovery process pressure
One day in October 1640, cloudless, far away from Florence, a well next to the Market Square, the famous Italian scientist Galileo pumps during the experiment. He put one end of the hose into the well water, then hose hanging on the wall three meters away from the wooden beams on the other end is connected to the manual pumps on. Pumps by Galileo's two assistants took, is the wealthy son of a - 32-year-old aspiring scientist Torricelli, Italian physicist Barry another Anne (Giovanni Baliani). Torricelli and Anne Barry shake the wooden handle pumps, hose of the air out slowly, slowly rising water in the hose. Pumps to suck the hose flat like drinking straws, it is no matter how hard they shake hands, the height of the surface water from the wells will not be over 9.7 meters. Each experiment like this. Galileo made: the weight of the water column in some way so that the water back to that height. 1643, Torricelli began to study the wonders of pumps. According to Galileo's theory, the heavy liquid can achieve the same critical weight, height is much lower. The density of mercury is 13.5 times of water, therefore, will not exceed the height of mercury column height of 1/13.5, that is about 30 inches. Torricelli of 6-foot-long glass tube fitted with mercury, with a cork plug opening segment. He reversed the glass tube, one end into the cork fitted with mercury in the basin. As he expected, pulled the cork, the mercury flows from the tube into the pot, but not all the mercury to flow out. Torricelli tube measured the height of mercury column, and he expect the same, the height of the mercury column is 30 inches. However, he still suspected the reason of this mystery and the vacuum above the mercury column. The next day, the wind and rain, rain pounding the windows, in order to study the vacuum above the mercury, Torricelli experiment over and over again. However, the day the mercury rose only to 29 inches in height. Torricelli puzzled, he hopes to rise yesterday, the mercury column height of the experiment. What is the difference of the two experiments at it? Rain kept pounding the glass, he plunged into meditation. A revolutionary new idea in the minds of Torricelli flash. Two experiments were conducted under different weather conditions, the air is also a weight. Pumps is not the truth of the mysteries of the liquid above it weight and a vacuum, but rather the weight of the surrounding atmosphere. Torricelli realized: the weight of the atmosphere in the air basin of mercury pressure, this pressure forces the mercury into the glass tube. The weight of glass and mercury in the atmosphere of mercury applied to the weight of the pot should be totally equal. The weight of the atmosphere changes, put it in the pot the pressure will increase or decrease, this will result in the glass tube mercury to rise or fall. The weight of the atmosphere would inevitably lead to changes in the weather changes. Torricelli discovered atmospheric pressure to find atmospheric pressure measurement and research methods.
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Encyclopedia
qiya Barometric pressure atmospheric pressure See weather elements.
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English Expression
: air-pressure, pressure, air pressure pneumatic pressure
n.: baro, atmospheric pressure, air pressure, barometric pressure