[img:64e6a333d0]http://www.phy.ntnu.edu.tw/demolab/phpBB/2/33_c4-62.gif[/img:64e6a333d0] What will happened if the spring is released. Click link for [url=http://www.phy.ntnu.edu.tw/demolab/phpBB/2/33_c4-62.mpg]Answer[/url] This center spring in this applet simulate the above situation.

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Fu-Kwun Hwang, Dept. Of Physics, National Taiwan Normal University.