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THE COMPASSREPRESENTEDBY:WEIDAI(wzd5010)XIAOYALI(xul115)YIQIAOZHU(yzz5070)COMPASS is a simple device for orientation identification.It is one of the four great inventions of ancient China that has exerted profound influence on the development of human civilization.WHAT IS A COMPASS?A compass consists of a rotational magnetic needle loaded on a shaft and a directional plate.WITH the meaning of“pointing to the south”,Si Nan was recorded in the great literature-Han Feizi during the Warring States Period(206BC-23AD)for identifying directions.It is the original basis for the invention of compass,and the OLDEST south-pointing device in human history.It is chiseled out of magnetic lodestone in the shape of a ladle or spoon.-si nanthe original compassIts handle will point south when put on the smooth Earth Plate used for divination,which contains 24 directions based on the magnetic meridian direction.H HISTORY ISTORY OOF F C COMPASSOMPASSTHE Chinese(121 A.D.)found that a suspended iron rod that had been exposed to a natural magnet(lodestone or magnetite)would align itself in the north-south direction.THE compass in real sense was created by a Chinese geomantic omen master in late Tang Dynasty,who originally used it for divination.The major material of the compass is magnetized steel needle,making up for the flaw that magnetism is easily lost in lodestones,of which Si Nan was made.The earliest compass was very complicated.In the Southern Song Dynasty,there were compasses with three or four layers of directions and later appeared compasses with seven or eight layers of directions.The accumulation of directions was due to the change of the Earths magnetic filed in ancient times or the different accounts of the ten Heavenly Stems and the Twelve Earthly Branches.It also had something to do with the mysterious nature of Fengshui masters trade.Later,the simple and clear mariners compass was created to meet the direction-finding need of marine navigation.The Compass Chariot(by Ma Jun,the Three Kingdoms period)The Compass Tortoise(by Chen Yuanliang,the Southern Song Dynasty)The Compass Fish(the Northern Song Dynasty)THE HISTORICAL FORMATSThere are also some other directional devices invented during the Chinese history.THEPHYSICALPRICIPLESHow are the lines similar to How are the lines similar to electric field lines?electric field lines?How can you tell that the How can you tell that the magnetic field is strongest magnetic field is strongest near the poles?near the poles?How can you tell that the Earths magnetic north is really like the south pole of a bar magnet?they pass out of N and into Smore concentrated therethe N-pole of the compass needle points towards itLike poles repel N+N or S+S and unlike poles N+S attract.THE PHYSICAL PRICIPLEShttp:/www.scifun.ed.ac.uk Earths magnetic field(and the surface magnetic field)is approximately a magnetic dipole,with one pole near the north pole(see Magnetic North Pole)and the other near the geographic south pole(see Magnetic South Pole).An imaginary line joining the magnetic poles would be inclined by approximately 11.3 from the planets axis of rotation.The cause of the field can be explained by dynamo theory.Magnetic fields extend infinitely,though they are weaker further from their source.The Earths magnetic field,which effectively extends several tens of thousands of kilometers into space,is called the magnetosphere.http:/en.wikipedia.org/wiki/Geomagnetichttp:/230nsc1.phy-astr.gsu.edu/hbase/magnetic/imgmag/mearthbar.gifhttp:/230nsc1.phy-astr.gsu.edu/hbase/magnetic/imgmag/magcon.gifMagnetic field concepts In ancient China,these compasses were used for two main reasons,and surprisingly,neither of these was for navigational purposes.The first was for town planning,to ensure that all houses were facing in a direction that was deemed harmonic with nature.The second was for geomancy,which is divination by geographic figures or pictures and lines,to determine the best location and time for such things as burials What Is Compass Use For?The Great Impact In Human HistoryThe first person to use the compass to travel in a ship was Zheng He(1371-1435)who made 7 voyages from 1405 to 1433.As metal ships developed in the 13 and 1400s,the metal interfered with the magnetic compass so the gyrocompass was developed because the metal did not interfere with its readings and it was incredibly accurate,even more so than the magnetized needles.navigation!1.Kjernsmo,K.(1997).How to use a compass.Retrieved February 9,2009,from http:/www.learn-orienteering.org/old/nocompass1.html2.Summer Research Program for Science Teachers.(2004,August).How do compasses work?Retrieved February 9,2009,from http:/www.scienceteacherprogram.org/physics/Omoloju04.html3.The Development of the Compass(2007).Retrieved February 9,2009,from http:/kaleidoscope.cultural- REFERENCES:
