PhET - Interactive Simulations, University of Colorado provides fun, interactive, research-based simulations of physical phenomena for free. Research-based approach - incorporating findings from prior research and our own testing - enables students to make connections between real-life phenomena and the underlying science, deepening their understanding and appreciation of the physical world.

To help students visually comprehend concepts, PhET simulations animate what is invisible to the eye through the use of graphics and intuitive controls such as click-and-drag manipulation, sliders and radio buttons. In order to further encourage quantitative exploration, the simulations also offer measurement instruments including rulers, stop-watches, voltmeters and thermometers. As the user manipulates these interactive tools, responses are immediately animated thus effectively illustrating cause-and-effect relationships as well as multiple linked representations (motion of the objects, graphs, number readouts, etc.)

To ensure educational effectiveness and usability, all of the simulations are extensively tested and evaluated. These tests include student interviews in addition to actual utilization of the simulations in a variety of settings, including lectures, group work, homework and lab work. A rating system indicates what level of testing has been completed on each simulation.