| 词条 | Magdeburg hemispheres |
| 释义 |
The Magdeburg hemispheres are a pair of large copper hemispheres, with mating rims. They were used to demonstrate the power of atmospheric pressure. When the rims were sealed with grease and the air was pumped out, the sphere contained a vacuum and could not be pulled apart by teams of horses. The Magdeburg hemispheres were designed by a German scientist and mayor of Magdeburg,[1] Otto von Guericke, to demonstrate the air pump that he had invented, and the concept of atmospheric pressure. The first artificial vacuum had been produced a few years earlier by Evangelista Torricelli, and had inspired Guericke to design the world's first vacuum pump, which consisted of a piston and cylinder with one-way flap valves. The hemispheres became popular in physics lectures as an illustration of the strength of air pressure, and are still used in education. A pair of the original hemispheres are preserved in the Deutsches Museum in Munich. OverviewThe Magdeburg hemispheres, around 50 cm (20 inches) in diameter,[2][3][4][5] were designed to demonstrate the vacuum pump that Guericke had invented. One of them had a tube connection to attach the pump, with a valve to close it off. When the air was sucked out from inside the hemispheres, and the valve was closed, the hose from the pump could be detached, and they were held firmly together by the air pressure of the surrounding atmosphere. The force holding the hemispheres together was equal to the area bounded by the joint between the hemispheres, a circle with a diameter of 50 cm, multiplied by the difference in air pressure between the inside and the outside. It is unclear how strong a vacuum Guericke's pump was able to achieve, but if it was able to evacuate all of the air from the inside, the hemispheres would have been held together with a force of around 20 000 N (4400 lbf, or 2.2 short tons),[6][7] equivalent to lifting a car or small elephant; a dramatic demonstration of the pressure of the atmosphere. DemonstrationsGuericke's demonstration was performed on 8 May 1654[8][9] in front of the Imperial Diet, and the Emperor Ferdinand III in Regensburg.[10] Thirty horses, in two teams of fifteen, could not separate the hemispheres until the valve was opened to equalize the air pressure. In 1656 he repeated the demonstration with sixteen horses (two teams of eight) in his hometown of Magdeburg, where he was mayor. He also took the two spheres, hung the two hemispheres with a support, and removed the air from within. He then strapped weights to the spheres, but the spheres would not budge. Gaspar Schott was the first to describe the experiment in print in his Mechanica Hydraulico-Pneumatica (1657). In 1663 (or, according to some sources, in 1661) the same demonstration was given in Berlin before Frederick William, Elector of Brandenburg with twenty-four horses. The experiment became a popular way to illustrate the principles of air pressure, and many smaller copies of the hemispheres were made, and are used to this day in science classes. Reenactments of von Guericke's experiment of 1654 are performed in locations around the world by the Otto von Guericke Society. On 18 March 2000, a demonstration using sixteen horses was conducted in Great Torrington by Barometer World. The experiment has been commemorated on at least two German stamps. After learning about Guericke's pump through Schott's book, Robert Boyle worked with Robert Hooke to design and build an improved air pump. From this, through various experiments, they formulated what is called Boyle's law, which states that the volume of a body of an ideal gas is inversely proportional to its pressure. Much later the ideal gas law was formulated in 1834. See also
References1. ^{{cite encyclopedia|title=Guericke, Otto von|encyclopedia=Encyclopædia Britannica, 11th Ed.|volume=12|pages=670|publisher=Cambridge Univ. Press|year=1910|url=https://books.google.com/books?id=GFAEAAAAYAAJ&pg=PA670}} 2. ^{{cite web|last=Hablanian|first=M. H.|author2=Hemeon, C. H.|title=Comments about Magdeburg hemispheres reenactment|work=50 years of the AVS|publisher=American Vacuum Society|year=2003|url=http://www2.avs.org/historybook/links/magden.htm|doi=|deadurl=yes|archiveurl=https://web.archive.org/web/20080803104623/http://www2.avs.org/historybook/links/magden.htm|archivedate=2008-08-03|df=}} 3. ^{{cite web|last=Nave|first=C.R.|title=Original Magdeburg Hemispheres|work=Hyperphysics|publisher=Dept. of Physics and Astronomy, Georgia State Univ.|year=2000|url=http://hyperphysics.phy-astr.gsu.edu/Hbase/Kinetic/pmdg.html}} 4. ^{{cite web|title=Magdeburg hemispheres|work=Multimedia Catalogue|publisher=Institute and Museum of the History of Science, Florence, Italy|year=2006|url=http://brunelleschi.imss.fi.it/museum/esim.asp?c=500014}} 5. ^{{cite book|last=Hall|first=Edwin H.|author2=Bergen, Joseph Y.|title=A Textbook of Physics, 3rd Ed.|publisher = Henry Holt & Co.|year=1903|location=New York|page=52|url=https://books.google.com/books?id=szoAAAAAYAAJ&pg=PA52&dq=Magdeburg+hemispheres}} 6. ^{{cite web | last = Nave | first = Carl R. | authorlink = | title = Magdeburg Hemispheres | work = Hyperphysics | publisher = Dept. of Physics and Astronomy, Georgia State Univ. | date = 2012 | url = http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/pmdg.html | doi = | accessdate = November 12, 2012}} 7. ^Calculated using a diameter of 0.5 m with atmospheric pressure; force is given by{{math| P₀ * π * r²}}, where P₀=air pressure and r=cross-sectional radius of the hemisphere. Due to the inefficiencies of the vacuum pump, the artificial vacuum was likely much weaker. 8. ^{{cite book |title=The Horizon: A History of Our Infinite Longing |first1=Didier |last1=Maleuvre |publisher=University of California Press |year=2011 |isbn=978-0-520-94711-5 |page=181 |url=https://books.google.com/books?id=pUldN1FCGmwC}} [https://books.google.com/books?id=pUldN1FCGmwC&pg=PA181 Extract of page 181] 9. ^{{cite book |title=Twenty-Two Turbulent Years 1639 - 1661 |first1=David C. |last1=Wallace |publisher=Fast-Print Publishing |year=2013 |isbn=978-1-78035-660-0 |page=156 |url=https://books.google.com/books?id=Mkpl2cBZn3gC}} [https://books.google.com/books?id=Mkpl2cBZn3gC&pg=PA156 Extract of page 156] 10. ^{{cite encyclopedia|title=Guericke, Otto von|encyclopedia=Encyclopædia Britannica, 11th Edition|volume=9|page=670|publisher=The Encyclopædia Britannica Co.|year=1910|url=https://books.google.com/books?id=GFAEAAAAYAAJ&pg=PA670&}}
External links{{Commons|Magdeburg hemispheres}}
3 : Physics experiments|Historical scientific instruments|Magdeburg |
| 随便看 |
|
开放百科全书收录14589846条英语、德语、日语等多语种百科知识，基本涵盖了大多数领域的百科知识，是一部内容自由、开放的电子版国际百科全书。