# Vacuum

views updated Jun 08 2018

# 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.

# Vacuum

views updated Jun 11 2018

# 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.

# Vacuum

views updated May 29 2018

# 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.

# vacuum

views updated May 23 2018

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.

# vacuum

views updated May 11 2018

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.