This applet was created many years ago with JDK1.0.2. You need to see the source code to find out the model.
Actually, it is a standard model in any physics text book. We can discuss it if you want.
For those applets created with EJS, you can click [b]load ejs as signed applet [/b]to see the model.
(You will be asked to grant the permission to load EJS into your computer, then the program will be run in a browser and you will see all the variables and equations used in the simulation in a GUI)
Please check out applets from another category: Easy Java Simulations (2001- )