There is no reset button allowing you to start the animation over. Currently you have to deduce the need to toggle the radio buttons to perform a reset or use the ?refresh? capability of your browser.
General Comments on Usability: Parameters can be changed on the fly, which is a nice touch. For large classroom display purposes a user may desire to re-script the applet for larger display. Information on how to script Physlets is described in the book Physlets: Teaching Physics with Interactive Curricular Material by Christian and Belloni.