Atmospheric pressure


It is important to know that air has weight and this idea probably seems a bit strange, because air seems very light, even at sea level. However, it must be remembered that the atmosphere extends to high altitudes. The atmospheric pressure is equal to the weight of a column of air over a unit area on the surface of the earth.


What is atmospheric pressure?

It is the pressure exerted by the air at any point within the atmosphere . It is the weight of the column of air that is at any point on the earth and that, consequently, results in the weight per unit of the surface .

  • Atmospheric pressure characteristics
  • History
  • How it is calculated
  • Formula
  • Measurement units
  • For what is this
  • Where there is higher atmospheric pressure
  • Effects edit
  • Importance
  • Examples of atmospheric pressure

Atmospheric pressure characteristics

The main characteristics of atmospheric pressure are the following:

  • It is measured by means of a unit called pascal .
  • A greater height in the atmosphere , the atmospheric pressure will be lower .
  • It is proportional to the density or the number of molecules per unit volume.
  • The atmospheric pressure variations are measured by a barometer .
  • In areas where the air is cold , the atmospheric pressure is much higher.
  • The higher the elevation is at a certain location, the lower the amount of air above it.


The origin of atmospheric pressure is found together with Evangelista Torricelli, an Italian born on October 15, 1609 . In 1627 he went to study science with the Benedictine Benedetto Castelli.

He studied the work ” Dialogue of the New Science , in Spanish”, through which he was inspired to create some of the mechanical principles. In 1632, Castelli contacted Galileo so that he could accept Torricelli’s work and for this reason he moved to Arcetri , where he joined Galileo until his death. After Galileo died, Torricelli yielded to the distinctions of Ferdinand II of Tuscany and was appointed the duke’s philosopher and mathematician and professor of mathematics at the Academy of Florence.

In 1643 he discovered the principle of the barometer , which demonstrated that if atmospheric pressure existed , motivating himself to refute the Aristotelian theory that said that “nature has a horror of vacuum.” The torr pressure unit was named in his memory. In 1644 he published his work on Geometric Opera.

How it is calculated

To achieve the measurement of atmospheric pressure, the barometer is used , of which we can find different types. The mercury barometer was an instrument invented by Torricelli , which simply consists of a U-shaped tube with a closed branch in which the vacuum has been drawn , so that the pressure in the highest part of this branch is zero.


The formula used to calculate atmospheric pressure is as follows:

a = ρgh

  • ρ is the density of mercury ρ = 13550 kg / m3
  • g is the acceleration due to gravity g = 9.81 m / s2
  • h is the height of the mercury column h = 0.76 m at sea level

Measurement units

Atmospheric pressure can be measured through different mechanisms, they are:

  • hPa or hectopascals : it is the most used unit in atmospheric science. The mean atmospheric pressure is 1013.25 hPa.
  • mb or millibar or thousands of bars : a bar is roughly the same as in atmosphere. Millibars and hPa are equivalent so the mean pressure is 1013.25 millibars.
  • atm which is short for atmosphere. The pressure of the earth’s surface depends on weather conditions.
  • psi or pound per square inch : is the average unit used by the United States aeronautical industry . The mean atmospheric pressure is 14.7 psi.
  • Inch of Hg or Inch of Mercury – Most commonly used, the mean pressure is 29.92 inches of Hg.
  • mm Hg or millimeters of Mercury : The mean pressure is 761.84 mm Hg.
  • Torr : It is named after the scientist Torricelli, the mean pressure of this unit is also 761.84 torr.

For what is this

The reason for the atmospheric pressure is the weight that the air has on a certain point of the earth’s surface, therefore, it can be assumed that the higher that point is, the pressure will be lower , since it is also lower the amount of air above it.

Where there is higher atmospheric pressure

The closer we are to sea level, the atmospheric pressure will be higher, as we are at higher altitudes , the pressure will decrease . It also has highs and lows depending on the humidity or the temperature of the surface. It is for this reason that the peoples that live in the mountains will have less pressure and those that are in plains, plains, coasts and deserts , will present greater pressure . The places that are located in the tropics will have a pressure variation according to the climatic seasons that they present in the year.

Effects edit

Some effects that occur due to atmospheric pressure are the following:

  • When there is low atmospheric pressure, the amount of oxygen that enters the blood through the lungs decreases .
  • In very high places, between 3000 and 4000 meters, mountain sickness can occur , characterized by headache, nausea and shortness of breath.
  • The pressure reduction may occur hypoxia , edema Pulmonary r and hemorrhages in the retina .


Atmospheric pressure is very important for man because it regulates the masses of cold and warm air on the earth, it helps to determine when there will be little or abundant rainfall . It influences the feeding of some animals, the scarcity of water and the climatic changes .

They also influence the different agricultural activities as it helps to know the regulation of rainfall, namely, which are the best agricultural activities depending on high or low temperatures.

Examples of atmospheric pressure

Some examples of atmospheric pressures are the following:

  • When we stick a suction cup on a surface that is smooth, avoiding air trapped inside, the atmospheric pressure keeps it firmly attached so that it does not fall under its weight.
  • If we place a heavy object on a table , the weight of this body will exert a certain pressure on the surface of the table.

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