Vacuum

context: Vacuum is space void of matter. The word stems from the Latin adjective vacuus for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often discuss ideal test results that would occur in a perfect vacuum, which they sometimes simply call "vacuum" or free space, and use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory or in space. In engineering and applied physics on the other hand, vacuum refers to any space in which the pressure is lower than atmospheric pressure. The Latin term in vacuo is used to describe an object as being in what would otherwise be a vacuum.
qas: answers: vacuus
question: The word Vacuum stems from what Latin adjective?

answers: imperfect vacuum
question: What does the term used by Physicists, partial vacuum, refer to?

answers: space void of matter
question: What is a vacuum?

answers: gaseous
question: What type of pressure is less than atmospheric pressure in a vacuum?

answers: in vacuo
question: What Latin term is used to describe an object in a vacuum?

context: The quality of a partial vacuum refers to how closely it approaches a perfect vacuum. Other things equal, lower gas pressure means higher-quality vacuum. For example, a typical vacuum cleaner produces enough suction to reduce air pressure by around 20%. Much higher-quality vacuums are possible. Ultra-high vacuum chambers, common in chemistry, physics, and engineering, operate below one trillionth (10−12) of atmospheric pressure (100 nPa), and can reach around 100 particles/cm3. Outer space is an even higher-quality vacuum, with the equivalent of just a few hydrogen atoms per cubic meter on average. According to modern understanding, even if all matter could be removed from a volume, it would still not be "empty" due to vacuum fluctuations, dark energy, transiting gamma rays, cosmic rays, neutrinos, and other phenomena in quantum physics. In the electromagnetism in the 19th century, vacuum was thought to be filled with a medium called aether. In modern particle physics, the vacuum state is considered the ground state of matter.
qas: answers: the ground state of matter.
question: The Vacuum state is considered what?

answers: reduce air pressure by around 20%
question: A typical vacuum cleaner produces enough suction to do what to air pressure?

answers: how closely it approaches a perfect vacuum
question: The quality of a partial vacuum refers to what?

answers: a few hydrogen atoms per cubic meter
question: Outer space has a high quality vacuum with what equivalent?

answers: it would still not be "empty"
question: If all matter is removed from a vacuum, would it be empty space?

context: Historically, there has been much dispute over whether such a thing as a vacuum can exist. Ancient Greek philosophers debated the existence of a vacuum, or void, in the context of atomism, which posited void and atom as the fundamental explanatory elements of physics. Following Plato, even the abstract concept of a featureless void faced considerable skepticism: it could not be apprehended by the senses, it could not, itself, provide additional explanatory power beyond the physical volume with which it was commensurate and, by definition, it was quite literally nothing at all, which cannot rightly be said to exist. Aristotle believed that no void could occur naturally, because the denser surrounding material continuum would immediately fill any incipient rarity that might give rise to a void.
qas: answers: no void could occur naturally,
question: What did Aristotle believe about a void?

answers: whether such a thing as a vacuum can exist.
question: What was historically disputed about vacuums?

answers: cannot rightly be said to exist
question: What did something that was literally nothing at all,According to Plato, mean?

answers: denser surrounding material continuum
question: Aristotle thought what would fill any rarity that might give rise to a void?

context: In his Physics, book IV, Aristotle offered numerous arguments against the void: for example, that motion through a medium which offered no impediment could continue ad infinitum, there being no reason that something would come to rest anywhere in particular. Although Lucretius argued for the existence of vacuum in the first century BC and Hero of Alexandria tried unsuccessfully to create an artificial vacuum in the first century AD, it was European scholars such as Roger Bacon, Blasius of Parma and Walter Burley in the 13th and 14th century who focused considerable attention on these issues. Eventually following Stoic physics in this instance, scholars from the 14th century onward increasingly departed from the Aristotelian perspective in favor of a supernatural void beyond the confines of the cosmos itself, a conclusion widely acknowledged by the 17th century, which helped to segregate natural and theological concerns.
qas: answers: 14th century
question: In what century did believes start to move away from Aristotle's idea regarding a void?

answers: Stoic physics
question: What thought process was used in the beginning belief of the existence of vacuums?

answers: 13th and 14th
question: Roger Bacon,Walter Burley and Blasius of Parma were from what century?

answers: a supernatural void beyond the confines of the cosmos itself
question: What belief regarding a cosmic void was accepted by most in the 17th century?

context: Rapid decompression can be much more dangerous than vacuum exposure itself. Even if the victim does not hold his or her breath, venting through the windpipe may be too slow to prevent the fatal rupture of the delicate alveoli of the lungs. Eardrums and sinuses may be ruptured by rapid decompression, soft tissues may bruise and seep blood, and the stress of shock will accelerate oxygen consumption leading to hypoxia. Injuries caused by rapid decompression are called barotrauma. A pressure drop of 13 kPa (100 Torr), which produces no symptoms if it is gradual, may be fatal if it occurs suddenly.
qas: answers: rupture of the delicate alveoli
question: What does Rapid decompression do to the lungs?

answers: rapid decompression
question: What causes barotrauma?

answers: 13 kPa (100 Torr),
question: What amount of pressure drop can kill you if it occurs suddenly?

answers: hypoxia
question: What does acceleration of oxygen consumption do?

answers: vacuum exposure
question: rapid decompression is more dangerous than what?

context: Almost two thousand years after Plato, René Descartes also proposed a geometrically based alternative theory of atomism, without the problematic nothing–everything dichotomy of void and atom. Although Descartes agreed with the contemporary position, that a vacuum does not occur in nature, the success of his namesake coordinate system and more implicitly, the spatial–corporeal component of his metaphysics would come to define the philosophically modern notion of empty space as a quantified extension of volume. By the ancient definition however, directional information and magnitude were conceptually distinct. With the acquiescence of Cartesian mechanical philosophy to the "brute fact" of action at a distance, and at length, its successful reification by force fields and ever more sophisticated geometric structure, the anachronism of empty space widened until "a seething ferment" of quantum activity in the 20th century filled the vacuum with a virtual pleroma.
qas: answers: that a vacuum does not occur in nature
question: What did Descartes believe about vacuums in nature?

answers: Descartes
question: Whose work with metaphysics would come to define the notion of empty space?

answers: Cartesian mechanical philosophy
question: What philosophy combined with Descartes to push quantum activity in the 20th century?

context: In 1930, Paul Dirac proposed a model of the vacuum as an infinite sea of particles possessing negative energy, called the Dirac sea. This theory helped refine the predictions of his earlier formulated Dirac equation, and successfully predicted the existence of the positron, confirmed two years later. Werner Heisenberg's uncertainty principle formulated in 1927, predict a fundamental limit within which instantaneous position and momentum, or energy and time can be measured. This has far reaching consequences on the "emptiness" of space between particles. In the late 20th century, so-called virtual particles that arise spontaneously from empty space were confirmed.
qas: answers: Paul Dirac
question: An infinite sea of particles with negative energy  was a model propesed by whom?

answers: 1930
question: What year was the Dirac sea modeled?

answers: late 20th century
question: When werer virtual particles confirmed?

answers: 1927,
question: What year was the uncertainty principle formed?

answers: Werner Heisenberg's uncertainty principle
question: What theorized that time and energy can be measured?

context: In general relativity, a vanishing stress-energy tensor implies, through Einstein field equations, the vanishing of all the components of the Ricci tensor. Vacuum does not mean that the curvature of space-time is necessarily flat: the gravitational field can still produce curvature in a vacuum in the form of tidal forces and gravitational waves (technically, these phenomena are the components of the Weyl tensor). The black hole (with zero electric charge) is an elegant example of a region completely "filled" with vacuum, but still showing a strong curvature.
qas: answers: The black hole
question: what is a perfect example of a filled vacuum showing a curvature?

answers: Einstein
question: Who's equations  helped to imply vanishing of the Ricci tensor?

answers: tidal forces and gravitational waves
question: what produces curvature in a vacuum?

answers: black hole
question: What has no electric charge?

context: But although it meets the definition of outer space, the atmospheric density within the first few hundred kilometers above the Kármán line is still sufficient to produce significant drag on satellites. Most artificial satellites operate in this region called low Earth orbit and must fire their engines every few days to maintain orbit.[citation needed] The drag here is low enough that it could theoretically be overcome by radiation pressure on solar sails, a proposed propulsion system for interplanetary travel.[citation needed] Planets are too massive for their trajectories to be significantly affected by these forces, although their atmospheres are eroded by the solar winds.
qas: answers: low Earth orbit
question: Where do most satellites operate?

answers: solar sails
question: What system could possibly be used for interplanetary travel?

answers: atmospheric density
question: why do satellites need to fire engines every few day to keep orbit?

answers: Kármán line
question: above what line location in outer space to satellites orbit?

context: In the medieval Middle Eastern world, the physicist and Islamic scholar, Al-Farabi (Alpharabius, 872–950), conducted a small experiment concerning the existence of vacuum, in which he investigated handheld plungers in water.[unreliable source?] He concluded that air's volume can expand to fill available space, and he suggested that the concept of perfect vacuum was incoherent. However, according to Nader El-Bizri, the physicist Ibn al-Haytham (Alhazen, 965–1039) and the Mu'tazili theologians disagreed with Aristotle and Al-Farabi, and they supported the existence of a void. Using geometry, Ibn al-Haytham mathematically demonstrated that place (al-makan) is the imagined three-dimensional void between the inner surfaces of a containing body. According to Ahmad Dallal, Abū Rayhān al-Bīrūnī also states that "there is no observable evidence that rules out the possibility of vacuum". The suction pump later appeared in Europe from the 15th century.
qas: answers: handheld plungers in water.
question: Al-Farabi concluded a perfect vacuum was incoherent using what?

answers: place (al-makan) is the imagined three-dimensional void between the inner surfaces of a containing body
question: Ibn al-Haytham used geometry to demonstrate  what?

answers: Abū Rayhān al-Bīrūnī
question: who stated that there was no evidence to rule out a vacuum?

answers: air's volume
question: what did Al-Farabi say expanded to fill available space

answers: suction pump
question: What type of pump appeared in the 15th century?

context: Medieval thought experiments into the idea of a vacuum considered whether a vacuum was present, if only for an instant, between two flat plates when they were rapidly separated. There was much discussion of whether the air moved in quickly enough as the plates were separated, or, as Walter Burley postulated, whether a 'celestial agent' prevented the vacuum arising. The commonly held view that nature abhorred a vacuum was called horror vacui. Speculation that even God could not create a vacuum if he wanted to was shut down[clarification needed] by the 1277 Paris condemnations of Bishop Etienne Tempier, which required there to be no restrictions on the powers of God, which led to the conclusion that God could create a vacuum if he so wished. Jean Buridan reported in the 14th century that teams of ten horses could not pull open bellows when the port was sealed.
qas: answers: Bishop Etienne Tempier
question: Who required no restrictions regarding God's power?

answers: 14th century
question: When did Buridan state that teams of ten horses could not open a bellow with a sealed port?

answers: God could create a vacuum if he so wished.
question: the 1277 Paris Condemnations led to what conclusion?

answers: nature abhorred a vacuum
question: What was a common belief about vacuums and nature?

answers: horror vacui
question: what was the belief that nature abhorred a vaccuum called?

context: In 1654, Otto von Guericke invented the first vacuum pump and conducted his famous Magdeburg hemispheres experiment, showing that teams of horses could not separate two hemispheres from which the air had been partially evacuated. Robert Boyle improved Guericke's design and with the help of Robert Hooke further developed vacuum pump technology. Thereafter, research into the partial vacuum lapsed until 1850 when August Toepler invented the Toepler Pump and Heinrich Geissler invented the mercury displacement pump in 1855, achieving a partial vacuum of about 10 Pa (0.1 Torr). A number of electrical properties become observable at this vacuum level, which renewed interest in further research.
qas: answers: partial vacuum of about 10 Pa (0.1 Torr).
question: What was the vacuum created by the mercury displacement pump?

answers: 1850
question: What year was the Toepler Pump invented?

answers: vacuum pump
question: What was first invented by Otto von Guericke ?

answers: Otto von Guericke
question: Who conducted the Magdeburg experiment?

answers: A number of electrical properties
question: What was made visible at a partial vacuum of 10 Pa?

context: While outer space provides the most rarefied example of a naturally occurring partial vacuum, the heavens were originally thought to be seamlessly filled by a rigid indestructible material called aether. Borrowing somewhat from the pneuma of Stoic physics, aether came to be regarded as the rarefied air from which it took its name, (see Aether (mythology)). Early theories of light posited a ubiquitous terrestrial and celestial medium through which light propagated. Additionally, the concept informed Isaac Newton's explanations of both refraction and of radiant heat. 19th century experiments into this luminiferous aether attempted to detect a minute drag on the Earth's orbit. While the Earth does, in fact, move through a relatively dense medium in comparison to that of interstellar space, the drag is so minuscule that it could not be detected. In 1912, astronomer Henry Pickering commented: "While the interstellar absorbing medium may be simply the ether, [it] is characteristic of a gas, and free gaseous molecules are certainly there".
qas: answers: aether
question: What was originally believed the heavens were filled with?

answers: "While the interstellar absorbing medium may be simply the ether, [it] is characteris
question: Why were experiments done on luminiferous aether in the 19 Century?

answers: Henry Pickering
question: Who stated that the character of a gas and free molecule were in ether?

answers: outer space
question: Where are the highest amounts of naturally occurring partial vacuums?

answers: rigid indestructible material
question: What was ether originally thought to be made of?

context: The quality of a vacuum is indicated by the amount of matter remaining in the system, so that a high quality vacuum is one with very little matter left in it. Vacuum is primarily measured by its absolute pressure, but a complete characterization requires further parameters, such as temperature and chemical composition. One of the most important parameters is the mean free path (MFP) of residual gases, which indicates the average distance that molecules will travel between collisions with each other. As the gas density decreases, the MFP increases, and when the MFP is longer than the chamber, pump, spacecraft, or other objects present, the continuum assumptions of fluid mechanics do not apply. This vacuum state is called high vacuum, and the study of fluid flows in this regime is called particle gas dynamics. The MFP of air at atmospheric pressure is very short, 70 nm, but at 100 mPa (~6997100000000000000♠1×10−3 Torr) the MFP of room temperature air is roughly 100 mm, which is on the order of everyday objects such as vacuum tubes. The Crookes radiometer turns when the MFP is larger than the size of the vanes.
qas: answers: amount of matter remaining in the system
question: What indicated the quality of a vacuum?

answers: its absolute pressure
question: How is vacuum generally measured?

answers: average distance that molecules will travel between collisions with each other.
question: What does the MFP of residual gases show?

answers: study of fluid flows
question: What is particle gas dynamics?

context: The SI unit of pressure is the pascal (symbol Pa), but vacuum is often measured in torrs, named for Torricelli, an early Italian physicist (1608–1647). A torr is equal to the displacement of a millimeter of mercury (mmHg) in a manometer with 1 torr equaling 133.3223684 pascals above absolute zero pressure. Vacuum is often also measured on the barometric scale or as a percentage of atmospheric pressure in bars or atmospheres. Low vacuum is often measured in millimeters of mercury (mmHg) or pascals (Pa) below standard atmospheric pressure. "Below atmospheric" means that the absolute pressure is equal to the current atmospheric pressure.
qas: answers: "Below atmospheric"
question: Absolute pressure  being equal to current atmospheric pressure means what?

answers: displacement of a millimeter of mercury
question: What is a torr equal to?

answers: barometric scale
question: What is another often used options to measure vacuum?

context: Hydrostatic gauges (such as the mercury column manometer) consist of a vertical column of liquid in a tube whose ends are exposed to different pressures. The column will rise or fall until its weight is in equilibrium with the pressure differential between the two ends of the tube. The simplest design is a closed-end U-shaped tube, one side of which is connected to the region of interest. Any fluid can be used, but mercury is preferred for its high density and low vapour pressure. Simple hydrostatic gauges can measure pressures ranging from 1 torr (100 Pa) to above atmospheric. An important variation is the McLeod gauge which isolates a known volume of vacuum and compresses it to multiply the height variation of the liquid column. The McLeod gauge can measure vacuums as high as 10−6 torr (0.1 mPa), which is the lowest direct measurement of pressure that is possible with current technology. Other vacuum gauges can measure lower pressures, but only indirectly by measurement of other pressure-controlled properties. These indirect measurements must be calibrated via a direct measurement, most commonly a McLeod gauge.
qas: answers: its high density and low vapour pressure
question: Why is mercury the better option for liquid used in a Hydrostatic gauge?

answers: Hydrostatic gauges
question: What is a vertical column of liquid in a tube which has different pressures at each end called?

answers: measure pressures ranging from 1 torr (100 Pa) to above atmospheric
question: What is a hydrostatic gauge used for?

answers: can measure vacuums as high as 10−6 torr
question: Why is the McLeod gauge special?

answers: McLeod gauge
question: An indirect measurement of pressure is most often calibrated by what?

context: Thermal conductivity gauges rely on the fact that the ability of a gas to conduct heat decreases with pressure. In this type of gauge, a wire filament is heated by running current through it. A thermocouple or Resistance Temperature Detector (RTD) can then be used to measure the temperature of the filament. This temperature is dependent on the rate at which the filament loses heat to the surrounding gas, and therefore on the thermal conductivity. A common variant is the Pirani gauge which uses a single platinum filament as both the heated element and RTD. These gauges are accurate from 10 torr to 10−3 torr, but they are sensitive to the chemical composition of the gases being measured.
qas: answers: Thermal conductivity gauges
question: The fact that gases ability to conduct heat decreases with pressure is used by what form of measurement?

answers: by running current through it
question: How is the wire filament in a Thermal conductivity gauge heated?

answers: chemical composition of the gases being measured
question: What is a Pirani gauge sensitive to?

answers: to measure the temperature of the filament
question: What is a RTD used for on a Thermal Conductivity gauge?

answers: 10 torr to 10−3 torr
question: A Pirani gauge is accurate within what ranges?

context: Ion gauges are used in ultrahigh vacuum. They come in two types: hot cathode and cold cathode. In the hot cathode version an electrically heated filament produces an electron beam. The electrons travel through the gauge and ionize gas molecules around them. The resulting ions are collected at a negative electrode. The current depends on the number of ions, which depends on the pressure in the gauge. Hot cathode gauges are accurate from 10−3 torr to 10−10 torr. The principle behind cold cathode version is the same, except that electrons are produced in a discharge created by a high voltage electrical discharge. Cold cathode gauges are accurate from 10−2 torr to 10−9 torr. Ionization gauge calibration is very sensitive to construction geometry, chemical composition of gases being measured, corrosion and surface deposits. Their calibration can be invalidated by activation at atmospheric pressure or low vacuum. The composition of gases at high vacuums will usually be unpredictable, so a mass spectrometer must be used in conjunction with the ionization gauge for accurate measurement.
qas: answers: the pressure in the gauge
question: What affects the number of ions in a gauge?

answers: mass spectrometer must be used in conjunction with the ionization gauge
question: What must be used for accurate measurement on the composition of gases at a high vacuums?

answers: Cold cathode gauges
question: What gauge is accurate from 10-2 torr to 10-9 torr?

answers: composition of gases at high vacuums will usually be unpredictable
question: Why does a mass spectrometer need to be used with gauge to be accurate at high vacuum gas measurement?

answers: hot cathode and cold cathode.
question: What are the two types of Ion gauges?

context: Cold or oxygen-rich atmospheres can sustain life at pressures much lower than atmospheric, as long as the density of oxygen is similar to that of standard sea-level atmosphere. The colder air temperatures found at altitudes of up to 3 km generally compensate for the lower pressures there. Above this altitude, oxygen enrichment is necessary to prevent altitude sickness in humans that did not undergo prior acclimatization, and spacesuits are necessary to prevent ebullism above 19 km. Most spacesuits use only 20 kPa (150 Torr) of pure oxygen. This pressure is high enough to prevent ebullism, but decompression sickness and gas embolisms can still occur if decompression rates are not managed.
qas: answers: sustain life at pressures much lower than atmospheric,
question: density of oxygen like that of sea-level atmosphere is needed to do what?

answers: of up to 3 km
question: What is the lowest altitude where acclimatization or a suit is not needed to prevent sickness in humans?

context: Humans and animals exposed to vacuum will lose consciousness after a few seconds and die of hypoxia within minutes, but the symptoms are not nearly as graphic as commonly depicted in media and popular culture. The reduction in pressure lowers the temperature at which blood and other body fluids boil, but the elastic pressure of blood vessels ensures that this boiling point remains above the internal body temperature of 37 °C. Although the blood will not boil, the formation of gas bubbles in bodily fluids at reduced pressures, known as ebullism, is still a concern. The gas may bloat the body to twice its normal size and slow circulation, but tissues are elastic and porous enough to prevent rupture. Swelling and ebullism can be restrained by containment in a flight suit. Shuttle astronauts wore a fitted elastic garment called the Crew Altitude Protection Suit (CAPS) which prevents ebullism at pressures as low as 2 kPa (15 Torr). Rapid boiling will cool the skin and create frost, particularly in the mouth, but this is not a significant hazard.
qas: answers: after a few seconds
question: When will a person or animal lose consciousness  when exposed to a vacuum?

answers: the Crew Altitude Protection Suit (CAPS)
question: A shuttle astronauts prevents ebullism at 2 kPa with what item?

answers: ebullism
question: What is the forming of gas bubbles in body fluids at a lowered pressure called?

answers: tissues are elastic and porous
question: What prevents body rupture at low altitude when human body is bloated by gas bubbles?

context: In ultra high vacuum systems, some very "odd" leakage paths and outgassing sources must be considered. The water absorption of aluminium and palladium becomes an unacceptable source of outgassing, and even the adsorptivity of hard metals such as stainless steel or titanium must be considered. Some oils and greases will boil off in extreme vacuums. The permeability of the metallic chamber walls may have to be considered, and the grain direction of the metallic flanges should be parallel to the flange face.
qas: answers: Some oils and greases
question: What can boil away in extreme vaccum exposure?

answers: parallel
question: How should the grain direct of metallic flanges run to flange faces?

answers: stainless steel or titanium
question: What are 2 metals that can be absorbed in an ultra high vacuum system?

answers: water absorption
question: What becomes a concern in an ultra high vacuum system regarding aluminum or palladium?

context: In quantum mechanics and quantum field theory, the vacuum is defined as the state (that is, the solution to the equations of the theory) with the lowest possible energy (the ground state of the Hilbert space). In quantum electrodynamics this vacuum is referred to as 'QED vacuum' to distinguish it from the vacuum of quantum chromodynamics, denoted as QCD vacuum. QED vacuum is a state with no matter particles (hence the name), and also no photons. As described above, this state is impossible to achieve experimentally. (Even if every matter particle could somehow be removed from a volume, it would be impossible to eliminate all the blackbody photons.) Nonetheless, it provides a good model for realizable vacuum, and agrees with a number of experimental observations as described next.
qas: answers: vacuum
question: The state with the lowest possible energy in quantum mechanics defines what ?

answers: QED
question: A vacuum state with no matter particles or photons is called what?

answers: impossible to eliminate all the blackbody photons
question: why is a QED vacuum impossible to achieve ?

answers: vacuum of quantum chromodynamics,
question: What is a QCD?

context: QED vacuum has interesting and complex properties. In QED vacuum, the electric and magnetic fields have zero average values, but their variances are not zero. As a result, QED vacuum contains vacuum fluctuations (virtual particles that hop into and out of existence), and a finite energy called vacuum energy. Vacuum fluctuations are an essential and ubiquitous part of quantum field theory. Some experimentally verified effects of vacuum fluctuations include spontaneous emission and the Lamb shift. Coulomb's law and the electric potential in vacuum near an electric charge are modified.
qas: answers: In QED vacuum
question: When are electric and magnetic fields with zero average values, but their variances are not at zero?

answers: spontaneous emission
question: What is a verified effect of vacuum fluctuation?

answers: virtual particles that hop into and out of existence
question: what is  vacuum fluctuation?

answers: vacuum energy
question: Finite energy in a QED is called what?

answers: vacuum near an electric charge
question: What modifies can Coulomb's Law in a vacuum?

context: Stars, planets, and moons keep their atmospheres by gravitational attraction, and as such, atmospheres have no clearly delineated boundary: the density of atmospheric gas simply decreases with distance from the object. The Earth's atmospheric pressure drops to about 6998320000000000000♠3.2×10−2 Pa at 100 kilometres (62 mi) of altitude, the Kármán line, which is a common definition of the boundary with outer space. Beyond this line, isotropic gas pressure rapidly becomes insignificant when compared to radiation pressure from the Sun and the dynamic pressure of the solar winds, so the definition of pressure becomes difficult to interpret. The thermosphere in this range has large gradients of pressure, temperature and composition, and varies greatly due to space weather. Astrophysicists prefer to use number density to describe these environments, in units of particles per cubic centimetre.
qas: answers: due to space weather
question: `Why does thermosphere past the Karman line vary so greatly?

answers: the Kármán line
question: What is commonly known as the boundary of outer space?

answers: number density
question: What do Astrophysicists use to describe outer space beyond the karman line?

answers: radiation pressure from the Sun and the dynamic pressure of the solar winds
question: What is more significant than isotropic gas pressure past the Karman line?

context: Vacuum is useful in a variety of processes and devices. Its first widespread use was in the incandescent light bulb to protect the filament from chemical degradation. The chemical inertness produced by a vacuum is also useful for electron beam welding, cold welding, vacuum packing and vacuum frying. Ultra-high vacuum is used in the study of atomically clean substrates, as only a very good vacuum preserves atomic-scale clean surfaces for a reasonably long time (on the order of minutes to days). High to ultra-high vacuum removes the obstruction of air, allowing particle beams to deposit or remove materials without contamination. This is the principle behind chemical vapor deposition, physical vapor deposition, and dry etching which are essential to the fabrication of semiconductors and optical coatings, and to surface science. The reduction of convection provides the thermal insulation of thermos bottles. Deep vacuum lowers the boiling point of liquids and promotes low temperature outgassing which is used in freeze drying, adhesive preparation, distillation, metallurgy, and process purging. The electrical properties of vacuum make electron microscopes and vacuum tubes possible, including cathode ray tubes. The elimination of air friction is useful for flywheel energy storage and ultracentrifuges.
qas: answers: incandescent light bulb
question: What was the object to use first in widespread manner process of vacuum?

answers: chemical inertness
question: What is produced by a vacuum and used in electron beam welding and vacuum frying?

answers: obstruction of air,
question: Hight to ultra-high vacuums removes what obstruction?

answers: Deep vacuum lowers the boiling point of liquids and promotes low temperature outgassing
question: How does freeze drying, distillation and metallurgy benefit from a deep vacuum?

answers: electron microscopes and vacuum tubes
question: What are two things made possible by the electrical properties of vacuum?

context: Manifold vacuum can be used to drive accessories on automobiles. The best-known application is the vacuum servo, used to provide power assistance for the brakes. Obsolete applications include vacuum-driven windscreen wipers and Autovac fuel pumps. Some aircraft instruments (Attitude Indicator (AI) and the Heading Indicator (HI)) are typically vacuum-powered, as protection against loss of all (electrically powered) instruments, since early aircraft often did not have electrical systems, and since there are two readily available sources of vacuum on a moving aircraft—the engine and an external venturi. Vacuum induction melting uses electromagnetic induction within a vacuum.
qas: answers: vacuum servo
question: What provides power assistance for auto brakes?

answers: engine and an external venturi
question: What are two available sources of vacuum on a moving airplane?

answers: protection against loss of all (electrically powered) instruments,
question: Why are the Attitude indicator and heading indicator vacuum-powered?

answers: drive accessories
question: What does a manifold vacuum do on a car?

answers: vacuum-driven windscreen wipers and Autovac fuel pumps
question: What no longer used accessories were powered by vacuum?

context: Evaporation and sublimation into a vacuum is called outgassing. All materials, solid or liquid, have a small vapour pressure, and their outgassing becomes important when the vacuum pressure falls below this vapour pressure. In man-made systems, outgassing has the same effect as a leak and can limit the achievable vacuum. Outgassing products may condense on nearby colder surfaces, which can be troublesome if they obscure optical instruments or react with other materials. This is of great concern to space missions, where an obscured telescope or solar cell can ruin an expensive mission.
qas: answers: outgassing
question: what is evaporation and sublimation in a vacuum?

answers: obscure optical instruments
question: Why can outgassing products ruin a space mission?

answers: vacuum pressure falls below this vapour pressure
question: When does outgassing become important in all solid or liquid materials?

context: To continue evacuating a chamber indefinitely without requiring infinite growth, a compartment of the vacuum can be repeatedly closed off, exhausted, and expanded again. This is the principle behind positive displacement pumps, like the manual water pump for example. Inside the pump, a mechanism expands a small sealed cavity to create a vacuum. Because of the pressure differential, some fluid from the chamber (or the well, in our example) is pushed into the pump's small cavity. The pump's cavity is then sealed from the chamber, opened to the atmosphere, and squeezed back to a minute size.
qas: answers: continue evacuating a chamber indefinitely without requiring infinite growth
question: Repeatedly closing off a compartment of a vacuum allows what?

answers: a mechanism expands a small sealed cavity
question: How is a vacuum created inside of a manual water pump?

answers: Because of the pressure differential
question: Why is fluid in a manual pump pushed into the pumps cavity when a small sealed cavity is expanded?

answers: displacement pumps
question: What are pumps based off principle of sealed compartment pulling,pushing and expanding called?

context: The above explanation is merely a simple introduction to vacuum pumping, and is not representative of the entire range of pumps in use. Many variations of the positive displacement pump have been developed, and many other pump designs rely on fundamentally different principles. Momentum transfer pumps, which bear some similarities to dynamic pumps used at higher pressures, can achieve much higher quality vacuums than positive displacement pumps. Entrapment pumps can capture gases in a solid or absorbed state, often with no moving parts, no seals and no vibration. None of these pumps are universal; each type has important performance limitations. They all share a difficulty in pumping low molecular weight gases, especially hydrogen, helium, and neon.
qas: answers: Entrapment pumps
question: What pump can capture gases in a solid or absorbed state?

answers: no vibration.
question: Entrapment pumps often work without seals, moving parts and what else?

answers: Momentum transfer pumps
question: What pump has a higher quality vacuum than a positive displacement pump?

context: The lowest pressure that can be attained in a system is also dependent on many things other than the nature of the pumps. Multiple pumps may be connected in series, called stages, to achieve higher vacuums. The choice of seals, chamber geometry, materials, and pump-down procedures will all have an impact. Collectively, these are called vacuum technique. And sometimes, the final pressure is not the only relevant characteristic. Pumping systems differ in oil contamination, vibration, preferential pumping of certain gases, pump-down speeds, intermittent duty cycle, reliability, or tolerance to high leakage rates.
qas: answers: stages
question: When multiple pumps are connected in series to produce higher vacuum it is called what?

answers: vacuum technique
question: The choice of seals, or chamber geometry ,for example impact a pump. Together these are options are called what?

answers: oil contamination, vibration
question: What are two other relevant characteristics of a pumping system along with final pressure?