Java is required to run IWP. By this time, you should have it working on your computer.  The applets that you'll run are a bit different than the Physlets you've worked with.  IWP applets generally allow greater interactivity.  You can change some of the parameters, called inputs, in order to change the motion.  Screen captures with annotations showing various features of the IWP Animator and Graph windows are shown starting here.  These pages are also available on the Weekly Schedule page at the link IWP Help.

Tech Tip.  IWP problems may be accessed through a web link, which goes to the IWP server, or a standalone application. In the event that the IWP server is unavailable or blocked, download the application here. When prompted for a name for the file, enter "iwp.jar" in quotes to ensure that the extension is not altered. Annotated screen captures showing IWP features are available here. In order to use the application, just double click on the downloaded file to open it. No installation is required. Problem files are packaged with the application and may be opened using File -> Open -> Packaged.