What is the standard atmospheric pressure?

1 standard atmospheric pressure = 760 mm of mercury = 76 cm of mercury = 1.013 × 10^5 Pascal = 10.336 meters of water column.

The regulations of standard atmospheric pressure values ??have undergone several changes with the development of science and technology. It was originally specified that the atmospheric pressure at sea level at a temperature of 0°C, a latitude of 45°, and a clear day is the standard atmospheric pressure, which is approximately equivalent to a height of 76 centimeters of mercury. Later, it was discovered that the atmospheric pressure value under this condition is not stable and changes due to the influence of wind, temperature and other conditions. Therefore, the height of 76 centimeters of mercury was specified as the standard atmospheric pressure value. But later it was discovered that the pressure value as high as 76 centimeters of mercury was also unstable. The density of mercury changed due to the influence of temperature; the g value also changed with latitude.

In order to ensure that the standard atmospheric pressure is a fixed value, the resolution of the 10th International Conference on Weights and Measures in 1954 stated that the standard atmospheric pressure value is

1 standard atmospheric pressure = 101325 Newtons/㎡

"Teaching Reference Materials" Junior High School Physics Volume 1

Standard atmospheric pressure (QNE): refers to the air pressure at sea level under standard atmospheric conditions. Its value is 1013.2 hectopascals (or 760 millimeters of mercury high or 29.92 inches of mercury high).

The Earth is surrounded by thick air called the atmosphere. Air can flow as freely as water, but it is also affected by gravity. Therefore, there is pressure inside the air in all directions. This pressure is called atmospheric pressure. In 1654, Glick conducted the famous Magdeburg Hemisphere Experiment in Magdeburg, Germany, which gave people a profound understanding of atmospheric pressure, but people still don't know how big the atmospheric pressure is. Eleven years later, Italian scientist Torricelli filled an 80-centimeter-long thin glass tube with mercury and placed it upside down in a water tank filled with mercury. He found that the mercury in the glass tube dropped about 4 centimeters and then stopped falling. No air enters this 4 cm space, it is a vacuum. Torricelli concluded from this that the pressure of the atmosphere is equal to the length of the mercury column. According to the pressure formula, scientists have accurately calculated that the atmospheric pressure under standard conditions is 1.01×10^5Pa.

Changes in atmospheric pressure are related to altitude. Atmospheric pressure is generated by the gravity of the atmosphere. The higher you are from the ground, the thinner the atmosphere, and the lower the atmospheric pressure there should be. However, because air density, related to the gravitational force on the atmosphere, varies unevenly with height, the atmospheric pressure decreases unevenly with height.

Changes in atmospheric pressure are also related to weather. The atmospheric pressure in the same place is not exactly the same at different times. We know that the density of water vapor is smaller than that of air. When the air contains more water vapor, the density of the air becomes smaller and the atmospheric pressure also decreases. Generally speaking, the atmospheric pressure on a rainy day is lower than that on a sunny day. On a sunny day, if the atmospheric pressure suddenly decreases, it is a precursor to rain; if it rains for several consecutive days and the atmospheric pressure increases, it can be expected that the weather will soon turn sunny. In addition, changes in atmospheric pressure are also related to temperature. Because air density becomes smaller when the temperature rises, the atmospheric pressure is smaller when the temperature is high than when the temperature is low

Atmospheric pressure is not fixed. In order to compare the size of atmospheric pressure, at the 10th International Conference on Weights and Measures in 1954, scientists set a "standard" for atmospheric pressure: at sea level at 45° latitude, when the temperature is 0°C, a 760 mm high mercury column produces The pressure is called standard atmospheric pressure. Since it is a "standard", when calculating according to the liquid pressure formula, attention must be paid to the accuracy of the values ??of each physical quantity. From the relevant data, it can be found that the density of mercury at 0°C is 13.595×103 kg/m3, and the g value at sea level at 45° latitude is 9.80672 N/kg. Therefore, the pressure generated by a 760 mm high mercury column is

pmercury = ρmercury gh

=13.595×10^3 kg/cubic meter×9.80672 N/kg×0.76 m

=1.01325×10^5Pa.

This is the value of 1 standard atmosphere, recorded as 1atm.

In recent scientific work, for convenience, 1 standard atmosphere is defined as 100kPa, which is recorded as 1bar. Therefore, when we talk about standard atmospheric pressure, we can also refer to 100kPa.