According to the definition in physics, the concept of "vacuum" implies the absence of any substance and elements of matter in a certain space, in this case we speak of an absolute vacuum. A partial vacuum is observed when the density of the substance in a given place in space is low. Let's consider this question in more detail in the article.
Vacuum and pressure
The definition of the concept of "absolute vacuum" refers to the density of matter. From physics, it is known that if gaseous matter is considered, then the density of the substance is directly proportional to the pressure. In turn, when they talk about partial vacuum, they mean that the density of matter particles in a given space is less than that for air at normal atmospheric pressure. That is why the question of vacuum is a question of pressure in the system under consideration.
In physics, absolute pressure is a value equal to the ratio of force (measured in Newtons (N)), which is perpendicularly applied to a surface, to the surface area (measured in square meters), i.e. P = F / S, where P is the pressure , F is the force, S is the surface area. The unit of pressure is Pascal (Pa), it turns out that 1 [Pa] = 1 [N] / 1 [m 2 ].
Partial vacuum
It was experimentally established that at a temperature of 20 ° C on the surface of the Earth at sea level, atmospheric pressure is 101 325 Pa. This pressure is called the 1st atmosphere (atm.). Approximately we can say that the pressure is 1 atm. equals 0.1 MPa. Answering the question about how many atmospheres there are in 1 pascal, we compose the corresponding proportion and we get that 1 Pa = 10 -5 atm. A partial vacuum corresponds to any pressure in the space under consideration that is less than 1 atm.
If you translate these numbers from the language of pressure to the language of the number of particles, then it should be said that at 1 atm. 1 m 3 of air contains approximately 10 25 molecules. Any decrease in the indicated concentration of molecules leads to the formation of a partial vacuum.
Vacuum measurement
The most common instrument for measuring low vacuum is a conventional barometer, which can only be used when the gas pressure is several tens of percent of atmospheric pressure.
An electrical circuit with a Wheatstone bridge is used to measure higher vacuum values. The idea of use is to measure the resistance of a sensitive element, which depends on the surrounding concentration of molecules in the gas. The higher this concentration, the more molecules hit the sensitive element, and the more heat it transfers to them, this leads to a decrease in the temperature of the element, which affects its electrical resistance. This device manages to measure vacuum with pressures of 0.001 atm.
Historical reference
It is interesting to note that the concept of "absolute vacuum" was completely rejected by well-known ancient Greek philosophers, for example Aristotle. In addition, the existence of atmospheric pressure was not known until the beginning of the 17th century. Only with the advent of the New Time began experiments with tubes filled with water and mercury, which showed that the earth's atmosphere exerts pressure on all surrounding bodies. In particular, in 1648, Blaise Pascal was able to measure pressure at an altitude of 1000 meters above sea level using a mercury barometer. The measured value was much smaller than at sea level, thereby the scientist proved the existence of atmospheric pressure.
The first experiment, which clearly demonstrated the strength of atmospheric pressure, and also emphasized the concept of vacuum, was carried out in Germany in 1654, now it is known as the "experiment with the Magdeburg spheres." In 1654, the German physicist Otto von Guericke was able to tightly connect two metal hemispheres with a diameter of only 30 cm, and then pumped air out of the resulting structure, thereby creating a partial vacuum. History tells us that two teams of 8 horses each, which pulled in opposite directions, could not separate these spheres.
Absolute vacuum: does it exist?
In other words, is there a place in space that does not contain any matter. Modern technologies allow you to create a vacuum of 10 -10 Pa and even less, but this absolute pressure does not mean that there are no particles of matter in the system under consideration.
Let us turn now to the most empty space in the Universe - to open space. What is the pressure in the vacuum of space? The pressure in outer space around the Earth is 10 -8 Pa, at this pressure there are about 2 million molecules in a volume of 1 cm 3 . If we talk about intergalactic space, then, according to scientists, even in it there is at least 1 atom in a volume of 1 cm 3 . Moreover, our Universe is penetrated by electromagnetic radiation, the carriers of which are photons. Electromagnetic radiation is energy that can be converted into the corresponding mass according to the famous Einstein formula (E = m * c 2 ), that is, energy, along with matter, is a state of matter. It follows the conclusion that there is no absolute vacuum in the known Universe.