The earth is surrounded by thick air, which is called the atmosphere. Air can flow freely like water, and it is also influenced by gravity. So there is pressure in all directions in the air, and this pressure is called atmospheric pressure.
Italian scientist Torricelli filled an 80 cm long thin glass tube with mercury, and then put it upside down in a sink filled with mercury. He found that the mercury in the glass tube dropped by about 4 cm, and then stopped falling. Torricelli deduced from this that the pressure of the atmosphere is equal to the length of the mercury column. According to the pressure formula, scientists accurately calculated the atmospheric pressure in the standard state as1.01×105pa.
Extended data:
Air pressure change
The change of atmospheric pressure is related to altitude. Atmospheric pressure is produced by gravity in the atmosphere. The higher the ground, the thinner the atmosphere, and the smaller the atmospheric pressure should be. Change with height: atmospheric pressure decreases with the increase of height.
The change of atmospheric pressure is also related to the weather. At different times, the atmospheric pressure in the same place is not exactly the same. We know that the density of water vapor is less than that of air. When there is more water vapor in the air, the air density will become smaller and the atmospheric pressure will also decrease.
With climate change: Generally speaking, the air pressure is higher on sunny days than on cloudy days, higher in winter than in summer, and higher in morning than at noon.
Baidu encyclopedia-standard atmospheric pressure