Why do some people feel uncomfortable when the weather changes? Please explain this phenomenon with the knowledge of atmospheric pressure.

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Q: What factors are related to the change of atmospheric pressure? How did it change?

A: 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. However, because the air density related to the gravity received by the atmosphere varies unevenly with height, the atmospheric pressure decreases unevenly with 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. Generally speaking, the air pressure in rainy days is smaller than that in sunny days, and it is found that the sudden drop of air pressure in sunny days is a precursor to rain; However, after several days of continuous rain, it is found that the air pressure has become larger, and it can be expected that it will clear up soon. In addition, the change of atmospheric pressure is also related to temperature. Because the air density becomes smaller at high temperature, the atmospheric pressure is smaller at high temperature than at low temperature.

Q: What is the standard atmospheric pressure? How is its value obtained?

A: Atmospheric pressure is not fixed. In order to compare atmospheric pressure, at the 10th International Metrology Conference in 1954, scientists stipulated a "standard" for atmospheric pressure: at the sea level of latitude 45 and the temperature of 0℃, the pressure generated by a mercury column with a height of 760mm is called the standard atmospheric pressure. Since it is a "standard", we should pay attention to the accuracy of each physical quantity according to the formula of liquid pressure. According to relevant data, the density of mercury at 0℃ is 13.595× 103 kg/m3, and the g value at sea level at latitude 45 is 9.80672 N/kg. Therefore, it can be concluded that the pressure generated by a 760mm high mercury column is

P mercury = ρ mercury gh

= 13.595× 103kg/m3×9.80672N/kg×0.76m

= 1.0 1325× 105 Pa。

This is the value of 1 standard atmospheric pressure.