?, http://hk.knowledge.yahoo.com/question/?qid=7007061203035http://www.hk-phy.org/contextual/mechanics/for/force02_c.htmlhttp://mail.yejh.tc.edu.tw/~yang/303work/10%AA%BA3.htmhttp://sciedu.cc.nctu.edu.tw/gradstu/ping/web_final/teaching_source/teaching_f.asp :

http://hk.knowledge.yahoo.com/question/question?qid=7008040102280http://zh.wikipedia.org/wiki/%E7%89%9B%E9%A1%BF%E7%AC%AC%E4%B8%89%E5%AE%9A%E5%BE%8B :http://tw.knowledge.yahoo.com/question/question?qid=1008020204578 : 10 : 10 http://hk.knowledge.yahoo.com/question/?qid=7007050501653

http://hk.knowledge.yahoo.com/question/?qid=7007110603044http://hk.knowledge.yahoo.com/question/?qid=7007042202379 :http://www.lcsd.gov.hk/CE/Museum/Space/FAQ/explorer/c_faq_explorer_18.htm http://hk.knowledge.yahoo.com/question/?qid=7008012903293

http://macao838.com/viewthread.php?tid=137008 :http://hk.knowledge.yahoo.com/question/?qid=7008030701011 :http://hk.knowledge.yahoo.com/question/?qid=7006050102335 http://www.owls.tw/post/1/527http://www.pladaily.com.cn/pladaily/20000927/big5/20000927001241_society.html