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What is a vacuum? What is vacuum?

Many modern industries use vacuum chambers in the processing of their products, but what exactly is a vacuum and what is vacuum? Vacuum is the thinness of the gas in a vacuum. To really understand what vacuum is, we need to know the existence of atmospheric pressure and the pressure of atmospheric pressure, because both vacuum and vacuum are defined relative to the difference between atmospheric pressure and atmospheric pressure.
Speaking of atmospheric pressure we would do well to start with the famous Marburg hemisphere experiment, a scientific experiment carried out on 8 May 1654 by Otto von Glick, then mayor of Marburg in Germany, in order to prove the existence of atmospheric pressure in what is today the outskirts of Regensburg, Germany. Glick created two hollow copper hemispheres, approximately 50 cm in diameter, with a layer of leather impregnated with oil in the middle to allow the two hemispheres to fit perfectly together. One of the hemispheres had a connection tube to a vacuum pump, with a valve to close it. When the air is extracted from between the two hemispheres, the two hemispheres are pressed together by the surrounding atmosphere. Glick then divides 16 horses into two groups and pulls the two hemispheres in opposite directions. When the 16 horses finally pulled the two hemispheres apart with all their might, they made a loud noise, like a cannon being fired. This is the "power of air"! If the valve on the brass hemispheres is unscrewed, air flows into the ball through the valve and the ball opens when pulled by hand. This experiment demonstrates visually that by pulling air out of a confined space and leaving it in a near-airless state (i.e. a vacuum), there is a large pressure outside the ball. What exactly is this atmospheric pressure? Can we measure this experimentally? This brings us to another famous experiment - the Torricelli experiment.
On 20 June 1643, the Italian scientist Torricelli first measured the size of a standard atmospheric pressure of about 760 mm Hg using mercury, a long glass tube of more than 1 metre and a sink, hence the name Torricelli's experiment.
Diagram of Torricelli's experiment
Atmospheric pressure is not fixed, so in order to compare the magnitude of atmospheric pressure, at the 10th International Congress of Weights and Measures in 1954, scientists set a 'standard' for atmospheric pressure: at sea level at 45° latitude, when the temperature is 0°C, the pressure produced by a 760 mm high column of mercury is called the standard atmospheric pressure. is 13.595 x 103 kg/m³ and the value of g at sea level at 45° latitude is 9.80672 N/kg. The pressure generated by a 760 mm high column of mercury is then given as
p mercury = ρ mercury gh = 13.595 x 103 kg/m³ x 9.80672 N/kg x 0.76 m = 1.01325 x 105 Pa.
This is the value of 1 standard atmosphere, and vacuum = atmospheric pressure - absolute pressure (the actual pressure measured by the gauge). Is it now clear to you what vacuum is?

In the previous:What is the typical power of an industrial oven? The next article:The difference between the two types of vacuum drying ovens
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