la gravitation (2/3)

partie 1:
http://www.dailymotion.com/video/xde88e_la-gravitation-1-3_tech
partie 2:
http://www.dailymotion.com/video/xde8md_la-gravitation-2-3_tech
partie 3:
http://www.dailymotion.com/video/xde94m_la-gravitation-3-3_tech