nice one Andres Fernando Pedraza, and Malory Johana Sanchez From Bogotá. Colombia!

just like to say the facebook fan page connected more people using Ejs to come here
http://www.facebook.com/pages/Easy-Java-Simulation-Official/132622246810575


this duffing oscillator is cool
i read on
and found another cool applets to understand the Ejs version one by  afpedraza
http://www.math.udel.edu/~hsiao/m302/JavaTools/osduffng.html
http://www.peter-junglas.de/fh/physbeans/applets/duffingoscillator.html
http://www.scholarpedia.org/article/Duffing_oscillator they look like this [img]http://www.scholarpedia.org/wiki/images/thumb/e/e5/Duffing-MagnetelasticBeam.gif/212px-Duffing-MagnetelasticBeam.gif[/img]
Duffing oscillator is an example of a periodically forced oscillator with a nonlinear elasticity, written as
[img]http://www.scholarpedia.org/wiki/images/math/d/e/c/dec8d87618e1acdcb45b70ea44786b31.png[/img](1),
where the damping constant obeys , and it is also known as a simple model which yields chaos, as well as van der Pol oscillator.

from http://dynlab.mpe.nus.edu.sg/mpelsb/me4213/Duffing.html
Duffing oscillator, a 2 degree of freedom oscillator with cubic stiffness.
x’’ + ax’ + x3 – x = b cos(t)
The oscillator can exhibit chaotic (i.e. irregular) oscillations


Question:
how come the applet is 2 mass oscillating so what is the difference between the red and blue mass?
i open the evolution page and study
dv/dt = -k1*x/m*s*(b*x*x-1)-R/m*v+A*Math.cos(w*t)
dv1/dt = -k1*x1/m*s*(b*x1*x1-1)-R/m*v1+A*Math.cos(w*t)

is it to show despite the same equation and same initial conditions, the red and blue mass ends up differently to show chaos?