originally uploaded to french wiki, 12 avril 2006 à 18:42, by Theon, who made these comments:

Espace des phases pour le pendule simple. Chaque courbe est un arc paramétré ${\displaystyle t\to (\theta (t),{\dot {\theta }}(t))}$, où t est le temps, ${\displaystyle \theta (t)}$ est l'angle que fait à l'instant t le pendule avec la verticale descendante et ${\displaystyle {\dot {\theta }}(t)}$ est la vitesse angulaire, dérivée de ${\displaystyle \theta (t)}$ par rapport à t. ${\displaystyle \theta (t)}$ est en abscisse et ${\displaystyle {\dot {\theta }}(t)}$ en ordonnée. Les flèches indiquent le sens de parcours des arcs paramétrés.

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• Source : image créée par l'auteur (Theon)