《神奇的指南针》.ppt

神奇的指南针1指南针是利用磁铁指示方向的仪器神奇的指南针2指南针的原理指南针是我国古代发明的利用磁石指极性制成的指南仪器。因此,必须从磁石说起。3早在2000多年前汉代,中国人就发现山上的一种石头具有吸铁的神奇特性,并发现一种长条的石头能指南北,他们管这种石头叫做磁石。4古代的能工巧匠把磁石打磨凿雕成一个勺形,放在光滑如镜的底盘上,再铸上方向性的刻纹。这个磁勺在底盘上可以自由转动,停止转动时,勺柄指的方向就是正南,勺口指的方向就是正北,这就是我国祖先发明的世界上最早的指示方向的仪器,叫做司南。是世界上最早的“指南针”了。其中,“司”就是“指”的意思。56汉代司南7司南的使用方法使用时先把地盘放平,再把司南放在地盘中间,用手拨动勺柄,使它转动,等到司南停下来,勺柄所指方向就是南方。这种勺形司南直到八世纪时仍在使用。p://p://j/m/k/t/x/s/s/soiz/s/vbz3/s/mytu/s/5ri8/http://shop./51132188http://shop./51126246http://shop./49830982http://shop./50855587http://shop./51126374http://shop./51132012http://shop./50855990http://shop./51023652http://shop./51233435http://shop./50669897http://shop./50866272http://shop./51126857http://shop./50659133http://shop./51233066http://shop./51004630http://shop./51028921http://shop./50798552http://shop./51127898http://shop./51233029http://shop./51235754http://shop./50802582http://shop./50673234http://shop./50673283http://shop./50672593http://shop./50847408http://shop./50674016http://shop./50857820http://shop./50823805http://shop./50802033http://shop./50671718http://shop./51130583http://shop./51237631http://shop./49610836http://shop./51131153http://shop./51132080http://shop./50668455http://shop./50831388http://shop./51239193http://shop./50673281http://shop./50673437http://shop./50673209http://shop./51396617http://shop./48030644http://shop./51399270http://shop./51396689http://shop./51398726http://shop./51233072http://shop./51396819http://shop./51405322http://shop./41244405http://shop./51407226http://shop./51407253http://shop./48766441http://shop./51023949http://shop./51408617http://shop./51405313http://shop./51407269http://shop./51400366http://shop./51410378http://shop./51410288http://shop./16847049http://shop./51238418http://shop./51407265http://shop./48001267http://shop./51412426http://shop./50637206http://shop./51409188http://shop./51410820http://shop./51412641http://shop./50672234http://shop./49072519http://shop./49312439http://shop./51413018http://shop./51413260http://shop./48900764http://shop./513