http://en.wikipedia.org/wiki/Jean_le_Rond_d'Alembert
http://scienceworld.wolfram.com/biography/dAlembert.html
_ Teorema D'Alembert
http://www.youtube.com/watch?v=n_Ai-DdGaCQ
_ Lesson 2: D' Alembert's Principa
http://www.youtube.com/watch?v=AkaEr9m7ly4