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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

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

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

vacuumabloom, assume, backroom, bloom, Blum, boom, broom, brume, combe, consume, doom, entomb, exhume, flume, foredoom, fume, gloom, groom, Hume, illume, inhume, Khartoum, khoum, loom, neume, perfume, plume, presume, resume, rheum, room, spume, subsume, tomb, vroom, whom, womb, zoom •catacomb • heirloom • broadloom •taproom • guardroom • staffroom •darkroom • classroom • bathroom •bedroom, headroom •legroom • restroom •dayroom, playroom •saleroom • stateroom • salesroom •tearoom • green room • sickroom •anteroom • bridegroom • stockroom •strongroom • box room • washroom •storeroom • boardroom • ballroom •courtroom • houseroom • showroom •cloakroom • elbow room •poolroom, schoolroom •newsroom •gunroom, sunroom •mushroom • common room •workroom • hecatomb • vacuum •legume • volume • costume •Leverhulme

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Vacuum

Vacuum

Defined strictly in scientific terms, a vacuum is any space that has all of its matter removed. It is impossible to create a perfect vacuum in a laboratory on Earth because not every single atom can be removed. Even the so-called vacuum of outer space is not a true (perfect) vacuum because even it contains tiny amounts of gas spread over vast volumes of space. However, in everyday terminology, a vacuum is described as any volume of space where pressure is less than standard sea-level pressurethat is, atmospheric pressure of 29.92 in [760 millimeters]) of mercury (or, one atmosphere [1 atm]).

Thus, vacuum is a term that describes conditions where the pressure is lower than that of the atmosphere. A sealed container is said to be under vacuum in this case; whereas it is pressurized when the pressure is higher than atmosphere. In a vacuum, it becomes necessary to define pressure microscopically. This means that the pressure, or force per unit area, is determined by the number of collisions between the atoms or molecules present and the walls of the container.

The first experiments involving vacuum date back to 1644 when Italian physicist Evangelista Torricelli (16081647) worked with columns of mercury, leading to the first barometer (a device for measuring pressure). The famous experiment of German scientist and inventor Otto von Guericke (16021686) in 1654 demonstrated the astounding force of vacuum when he evacuated the volume formed by a pair of joined hemispheres and attached each end to a team of horses that were unable to pull the hemispheres apart.

In order to create a vacuum, some kind of pump is needed. Simple mechanical pumps create a pressure difference, or suction force, which can be sufficient to pump water, for example. The most common use of pressure difference, the vacuum cleaner, is simply a chamber and hose, which are continuously evacuated by a fan (but the pressure difference created is far from a vacuum). Sophisticated vacuum pumps must be sealed to prevent air from leaking back into the pumping volume too quickly. These pumps increase in complexity, as better vacuums are needed. Pumps can generally be grouped into two categories: dynamic pumps, using mechanical or turbo-molecular action, and static pumps, using electrical ionization or low temperature (cryogenic) condensation.

Vacuum is important for research and industry, especially for manufacturing. Many industrial processes require vacuum either to be efficient or to be possible at all. Vacuum can be used for the prevention of chemical reactions, such as clotting in blood plasma or the removal of water in the process of freeze drying. Vacuum is also necessary for the prevention of particle collisions with background gas, in a television picture tube for example. For the fabrication of integrated electronics, it is very important to avoid impurities on a microscopic scale. It is only with excellent vacuum that such conditions can be obtained.

See also Atmospheric pressure; Vacuum tube.

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Vacuum

Vacuum

Vacuum is a term that describes conditions where the pressure is lower than that of the atmosphere. A sealed container is said to be "under vacuum" in this case whereas it is "pressurized" when the pressure is higher than atmosphere. In a vacuum, it becomes necessary to define pressure microscopically. This means that the pressure, or force per unit area, is determined by the number of collisions between the atoms or molecules present and the walls of the container.

The first experiments involving vacuum date back to 1644 when Evangelista Torricelli worked with columns of mercury, leading to the first barometer (a device for measuring pressure). The famous experiment of Otto von Guericke in 1654 demonstrated the astounding force of vacuum when he evacuated the volume formed by a pair of joined hemispheres and attached each end to a team of horses that were unable to pull the hemispheres apart.

In order to create a vacuum, some kind of pump is needed. Simple mechanical pumps create a pressure difference, or suction force, which can be sufficient to pump water , for example. The most common use of vacuum, the vacuum cleaner, is simply a chamber and hose which are continuously evacuated by a fan. More sophisticated vacuum pumps must be sealed to prevent air from leaking back into the pumping volume too quickly. These pumps increase in complexity as better vacuum is needed. Pumps can generally be grouped into two categories: dynamic pumps, using mechanical or turbo-molecular action, and static pumps, using electrical ionization or low temperature (cryogenic) condensation.

Vacuum is important for research and industry, especially for manufacturing. Many industrial processes require vacuum either to be efficient or to be possible at all. Vacuum can be used for the prevention of chemical reactions , such as clotting in blood plasma or the removal of water in the process of freeze drying. Vacuum is also necessary for the prevention of particle collisions with background gas, in a television picture tube for example. For the fabrication of integrated electronics , it is very important to avoid impurities on a microscopic scale. It is only with excellent vacuum that such conditions can be obtained.

See also Atmospheric pressure; Vacuum tube.

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