This paper outlines the design of an interactive simulation of Stokes' law, which is used frequently in the study of particle sedimentation and flotation. The software application includes dynamic visualizations and statistical outputs. Descriptions of how the simulation can be used in a teaching context are provided. The application and its source code are made freely available for inspection and modification by educators and students. As a "translucent box", the inner workings of the application are exposed to the interested user. It is suggested that the approach outlined can serve as a sustainable model for the development and preservation of software for science education.