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vacuum

vacuum, theoretically, space without matter in it. A perfect vacuum has never been obtained; the best man-made vacuums contain less than 100,000 gas molecules per cc, compared to about 30 billion billion (30×1018) molecules for air at sea level. The most nearly perfect vacuum exists in intergalactic space, where it is estimated that on the average there is less than one molecule per cubic meter. In ancient times the belief that "nature abhors a vacuum" was held widely and persisted without serious question until the late 16th and early 17th cent., when the experimental observations of Galileo and the Italian physicist Evangelista Torricelli demonstrated its essential fallacy. Torricelli obtained a nearly perfect vacuum (Torricellian vacuum) in his mercury barometer. A common but incorrect belief is that a vacuum causes "suction." Actually the apparent suction caused by a vacuum is the pressure of the atmosphere tending to rush in and fill the unoccupied space. There are various methods for producing a vacuum, and several different kinds of vacuum pumps have been devised for removing the molecules of gas or vapor from a confined space. In the rotary oil-sealed pump a rotor turning in a cylinder allows gas to enter through an inlet valve from a space to be evacuated and then pushes it through an outlet valve into the atmosphere. In the oil or mercury diffusion pump, gas enters the pump through an inlet and is then swept toward an outlet by heavy, fast-moving oil or mercury vapor molecules. The outlet is connected to a rotary pump that expels the gas into the atmosphere. A cryogenic pump removes gas from a container by condensing the gas molecules on an extremely cold surface in the container. An ion pump consists of a chamber containing a source of electrons that are used to bombard gas molecules from a container to be evacuated. Collisions between the electrons and gas molecules ionize the molecules, causing them to be drawn to, and held by, a collector in the pump. The first vacuum pump was invented by the German physicist Otto von Guerricke in 1650. There are many practical applications of vacuums in industry and scientific research, e.g., in vacuum distillation, vacuum processing of food, in devices such as the vacuum tube, vacuum bottle, and barometer, and in research machines.

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"vacuum." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 27 Apr. 2017 <http://www.encyclopedia.com>.

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Vacuum

Vacuum

The term vacuum has two different meanings. In its strictest sense, a vacuum is a region of space completely lacking any form of matter. The term represents absolute emptiness. One problem with this definition is that it describes an ideal condition that cannot exist in the real world. No one has ever discovered a way to make a perfect vacuum of this kind.

For that reason, the term vacuum also is used to describe regions of space from which the greatest possible amount of matter has been removed. In most cases, a vacuum is a container from which all gases have been removed as completely as possible.

Actually, the closest thing to a perfect vacuum is outer space. Astronomers believe that the space between stars consists in some cases of no more than a single atom or molecule per cubic kilometer. No vacuum produced on Earth comes even close to this condition.

The usual procedure for making a vacuum is with a vacuum pump. The pump, which consists of a piston (a sliding valve) in a cylinder, is attached to a closed container. With each stroke of the pump, some of the gas in the container is removed. The longer the pump operates, the better the vacuum produced in the container. To achieve the very best vacuums, however, special types of equipment are necessary.

Vacuums have many applications in scientific research, industry, and everyday life. Perhaps the most common example of the use of a vacuum is the household vacuum cleaner. The fan in a vacuum cleaner continually removes air from a canister, creating a partial vacuum. Atmospheric pressure outside the vacuum cleaner pushes air into the canister, taking along with it dust and dirt stirred up by the brush at the front of the vacuum cleaner.

Another common application of vacuums is a thermos bottle. A thermos bottle consists of two bottles, one nested inside the other. The space between the two bottles consists of a vacuum. In the absence of air, heat does not pass between the two bottles very easily. Hot liquids inside the container retain their heat, and cold liquids stay cold because heat cannot pass into them.

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vacuum

vac·u·um / ˈvakˌyoō(ə)m; -yəm/ • n. (pl. -u·ums or -u·a / -yoōə/ ) 1. a space entirely devoid of matter. ∎  a space or container from which the air has been completely or partly removed. ∎  [usu. in sing.] a gap left by the loss, death, or departure of someone or something formerly playing a significant part in a situation or activity: the political vacuum left by the death of the Emperor. 2. (pl. -u·ums) a vacuum cleaner. • v. [tr.] clean with a vacuum cleaner: the room needs to be vacuumed. PHRASES: in a vacuum (of an activity or a problem to be considered) isolated from the context normal to it and in which it can best be understood or assessed.

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"vacuum." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 27 Apr. 2017 <http://www.encyclopedia.com>.

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vacuum

vacuum Region of extremely low pressure. Interstellar space is a high vacuum, with an average density of less than 1 molecule per cubic centimetre; the highest man-made vacuums contain less than 100,000 molecules per cubic centimetre. The common laboratory device for reducing pressure in a container is a vacuum pump. Italian physicist Evangelista Torricelli is credited with developing (1643) the first man-made vacuum in a mercury barometer.

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"vacuum." World Encyclopedia. . Encyclopedia.com. 27 Apr. 2017 <http://www.encyclopedia.com>.

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vacuum

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"vacuum." Oxford Dictionary of Rhymes. . Encyclopedia.com. 27 Apr. 2017 <http://www.encyclopedia.com>.

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"vacuum." Oxford Dictionary of Rhymes. . Retrieved April 27, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/vacuum