Air Pressure Gages

Air pressure gauges are instruments that measure the atmosphere of the earth. Objects in the atmosphere are subjected to pressure generated by the impact of air molecules; the pressure is known as atmospheric pressure. It can also be argued that atmospheric pressure is the pressure caused by the gravity of the atmosphere itself. Due to the gravity effect, the gravitational pull of the earth is strong at the surface, so the density of air molecules is high, leading to high frequency of impact and greater atmospheric pressure. On the contrary, the gravitational pull of earth is relatively weak at places far from its surface, so the density of air molecules is low; the frequency of impact is lower, resulting in lower atmospheric pressure. Therefore, the atmospheric pressure at different altitudes on earth is different -- higher the position, lower the atmospheric pressure. In addition, the temperature and humidity of the air also have an effect on atmospheric pressure.

In physics, the annual average atmospheric pressure of the sea level on the latitude of 45 degrees (that means the altitude is zero) is defined as 1 standard atmospheric pressure (ATM). The standard atmospheric pressure is a constant value which equals to 760 mm Hg, 1.033 technical atmosphere, 1.0133 × 10⒌Pa and 0.10133MPa. The generation of atmospheric pressure is the result of the gravitational pull of earth, which attracts the atmosphere to earth and causes pressure. The air pressure near the ground is the largest. The atmospheric pressure in meteorological science refers to the weight of the atmosphere column (atmospheric pressure) per unit area, that is, the pressure imposed on the unit area by the column of the atmosphere.