https://kentikuhon.com/registered-architect11/
http://wwwra.meijo-u.ac.jp/labs/ra007/murata/onlinetext/mecha/step5-2.htm
http://kakukikaku.com/zusin.html
https://bonperson-civil.com/question-str004/
https://bonperson-civil.com/statical-moment-of-area/
http://kentiku-kouzou.jp/danmen1zi.html
http://physio-hachioji.com/center-of-mass.html