Interactive simulations of physical phenomena
"PhET provides interactive, research-based simulations of physical phenomena. They enable students to make connections between real-life phenomena and the underlying science, deepening their understanding and appreciation of the physical world."
"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."