A double pendulum is a pendulum with another pendulum attached to its end, and is a simple physical system[?] that exhibits rich dynamic behavior[?]. The double pendulum is governed by very complicated formulas that can be found here (http://scienceworld.wolfram.com/physics/DoublePendulum). The double pendulum relates to:
... and opens in the vulva between the clitoris and the vaginal opening.
In the human male, the urethra is about 8 inches (200 mm) long and opens at the end of the penis. ...