Computer simulations of physical phenomena have been a staple of physics teaching for decades. However, most physics simulations are of the sort where a user picks initial conditions, hits a "start" button, and then watches to see what occurs. While such simulations can be very instructive, especially if the user experiments with a variety of conditions, it is somewhat of an exaggeration to call such simulations "interactive". Interactivity, specifically "interactive engagement", is seen by most physics education researchers as a critical component to any truly successful physics curriculum. Without engaging the students' minds, forcing them to participate in an active role, conceptual learning is minimal.