Expanding knowledge-vacuum
The meaning of vacuum refers to the state of gas below one atmosphere in a given space, which is a physical phenomenon. In the "void", because there is no medium, sound cannot spread, but the propagation of electromagnetic waves is not affected by vacuum. In vacuum technology, vacuum refers to the atmosphere, and some substances in a specific space are discharged to make its pressure less than a standard atmospheric pressure, so we generally call this space a vacuum or vacuum state.
Historical allusion
From 65438 to 0654, otto von gehrig, the mayor of Fort Madre, showed his hemispheric experiments to the emperor in regensburg. He made two red copper hemispheres with a diameter of 5 1 cm, and there was a layer of leather soaked in oil in the middle of the hemispheres, so that the two hemispheres could be completely sealed. Then he pumped the air out of the ball with a homemade vacuum pump. At this time, the two heavy copper hemispheres are closely combined without any adhesive, which is very surprising.
But the climax of Gehrig's experiment has just begun, in order to prove how close and firm the two hemispheres are. The mayor pulled 16 horse, divided into two teams and pulled hard. There was a loud noise and the two hemispheres were pulled apart. This is the famous "Madeborg Hemisphere Experiment" in the history of physics.
Vacuum classification
Many modern high-precision products, such as semiconductors, hard disks and lenses, must be manufactured by using different degrees of vacuum at some stages of the manufacturing process. The method of making vacuum in laboratories and factories is to pump the air out of the closed space to achieve a certain degree of vacuum. In vacuum technology, we can divide it into coarse vacuum, medium vacuum, high vacuum and ultra-high vacuum according to pressure.
basic concept
From its etymology, it originally refers to emptiness, that is, space with nothing. Vacuum in industry and vacuum science means that when the pressure in the container is lower than atmospheric pressure, the part below atmospheric pressure is called vacuum, and the pressure in the container is called absolute pressure. To put it another way, the space in a container with a pressure below atmospheric pressure is called vacuum.
There are some differences in industrial vacuum: when there is no pressure in the container, that is, the absolute pressure is equal to zero, it is called complete vacuum; The rest is called an incomplete vacuum. Vacuum in Dirac's previous physical theory, such as special relativity, refers to the spatial state without any matter, which corresponds to the complete vacuum in industry.