a teacher recently shown me an exe file that can simulate SHM with a motor as driver.
it is should not be surprising (imperfect information flow) but i am always "surprise" (i thought google will surface this applet well and everyone searches the internet for applets) despite this applet being on the internet freely assessable, it is not widely known.
Information or innovative simulations like those made in Ejs is indeed difficult to diffuse and make it to teachers classroom use :)

anyway i improve this version of the SHM and concentrate on what are my interests/excites me.
09 February 2011
7 added more hints
8 added motor plunger as the right wall now moves with the externalForce(t) = amplitude * Math.sin(frequency*time); for greater association to possible real life setup
9 move top check-boxes hints to bottom as well for standard menu control

made some animated gif uploaded here as well as http://weelookang.blogspot.com/2010/06/ejs-open-source-simple-harmonic-motion.html for google to crawl