Download
1 / 25
260 likes | 479 Views
Agnese Caruso Liceo Classico C.Colombo. Vacuum. The Vacuum is a volume of space that is essentially empty of matter. The word comes from the Latin and it means “empty”.
E N D
Agnese Caruso • Liceo Classico C.Colombo Vacuum
The Vacuum is a volumeof spacethat is essentially empty of matter. The word comes from the Latin and it means “empty”. The so called “perfect vacuum” is a vacuum in wich can't be found any sort of particles, but it's impossible to create a perfect vacuum in practice.
Vacuum has been a frequent topic of philosophical debate since ancient Greek times, but was not studied empirically until the 17th century: the first who create a laboratory vacuum was Evangelista Torricelli in 1643. From his studyes about atmospheric pressure were developed other techniques. A torricellian vacuum is created by filling a tall glass container closed at one end with mercury and then inverting the container into a bowl to contain the mercury.
Its first 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 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 make the thermal insulation of thermos bottles possible. Deep vacuum makes the boiling point of liquids lower 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 airfriction is useful for flywheel energy storage and ultracentrifuges.
The vacuum is also commonly used to produce suction, that has a wide variety of applications.The Newcomen steam engine used vacuum instead of pressure to drive a piston. In the 19th century, vacuum was used for traction on Isambard Kingdom Brunel's experimental atmospheric railway (ferrovia pneumatica). Vacuum brakes were once widely used on trains in the UK but, except on heritage railways (ferrovia turistica), they have been replaced by air brakes.
Outer space is the closest physical approximation of a perfect vacuum because it has a very low density and pressure. It has no friction, so stars, planets and moons are allowed to move freely in the space. But no vacuum is truly perfect, not even in interstellar space, where there are still a few hydrogen atoms per cubic centimetre.
In the past studiers had already spoke about the existation of empty: Greek philosopher didn't admit the vacuum because they couldn't imagine that it was possible having something that isn't something real. Plato found the idea of a vacuum inconceivable. He believed that all physical things were copies of “ideas” that are out of our world and he could not conceive of an "ideal" form of a vacuum.
Also Aristotle doesn't know how to create a vacuum because “nothing” can't be something. Later Greek philosophers thought that a vacuum could exist outside the cosmos, but not within it.
Hero of Alexandria was the first that tryed to create a vacuum in the first century AD, but he failed.
In Pompeii, Roman city, a dual-action suction pump was found, wich proves that the ancient Romans had access to this kind of technology. Used for raising water, this pump had two cylinders, alternately operated by a walking-beam pump. In the suction phase, a lower valve opened, permitting the entry of water into the cylinder, while an upper valve remained closed. When the piston went down, the lower valve closed and the upper one opened.
Also in the Islamic regions some physicists like Al-Farabi conducted a small experiment concerning the existence of vacuum, in which he investigated handheld plungers in water.He concluded that air's volume can expand to fill available space, and he suggested that the concept of perfect vacuum was incoherent.Using geometry, Ibn al-Haytham, another physicist, who disagreed with Aristotle and Al-Farabi, demonstrated matematically that place (al-makan) is the imagined three-dimensional void between the inner surfaces of a containing body.
The first sunction pump was described in 1206 by Al Jazari, Muslim engineer and inventor. The suction pump later appeared in Europe from the 15th century. Taqui al-Din invented in 1551 a six-cylinder “Monobloc”, wich could create a partial vacue.
The Catholic Church regarded the idea of a vacuum as against nature or even heretical; the absence of anything implied the absence of God. In this period there was a common view called “horror vacui” for wich nature abhorred the empty space and they thought also that even God couldn't create a vacuum.
Renè Descartes also was against the existence of a vacuum, arguing along the following lines: "Space is identical with extension, but extension is connected with bodies; thus there is no space without bodies and hence no empty space (vacuum)." After Renè Descartes most of the scientists during the Scientific Revolution were against the existance of vacuum.
The belief in horror vacui was overthrown in the 17th century. Water pump designs produced measurable vacuums, but this was not immediately understood. What was known was that suction pumps could not pull water beyond a certain height: 18 Florentine yards according to a measurement taken around 1635 (The conversion to metres is uncertain, but it would be about 9 or 10 metres). This limit was a concern to irrigation projects, mine drainage, and decorative water fountains planned by the Duke of Tuscany, who commissioned Galileo to investigate the problem.
Galileo spoke about his investigations with other scientists, including Gasparo Berti who builds the first water barometer in Rome in 1639. Berti's barometer produced a vacuum above the water column, but he could not explain it.
The breakthrough was made by Evangelista Torricelli in 1643. With Galileo's notes, he built the first mercury baromether and wrote a convincing argument for wich the space at the top was a vacuum.
Some people believe that although Torricelli's experiment was crucial, it was Blaise Pascal's experiments that proved the top space really contained vacuum.
In 1654, Otto Von Guericke invented the first vacuum pump and conducted his famous Magdeburg Hemisphere 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 conducted experiments on the properties of vacuum.
The study of vacuum then lapsed until 1850 when August Toepler invented the Toepler pump . Then in 1855 Heinrich Gassler invented the mercury displacement pump and achieved a record vacuum of about 10 Pa (0.1 Torr ). A number of electrical properties become observable at this vacuum level, and this renewed interest in vacuum. This, in turn, led to the development of the vacuum tube. Shortly after this Hermann Sprengel invented the Sprengel pump in 1865.
Sources: Wikipedia
