求压力 压强的公式
http://cnc.lobit.cn/educa/unvisity/zxxzt/e9/xfzd/8.htm
http://sx.chinavnet.com/hg_school/C2/WL/HG/WL_12_02_005/index.html
http://cnc.lobit.cn/educa/unvisity/zxxzt/e9/xfzd/8.htm
http://sx.chinavnet.com/hg_school/C2/WL/HG/WL_12_02_005/index.html