The nerve-rattling plunges and loop-the-loops that come with most modern roller coasters are the best (and hopefully safest) places to become part of an extreme physics experiment. While modern roller coasters have become high-tech thrillers, the basic principle of starting at the top of a steep hill and rolling around a track till you run out of energy is still the basis of most of the rides. In this way roller coasters embody one of the most important ideas in all of physics: the Conservation of Energy. Roller coasters turn gravitational potential energy into kinetic energy of the car’s (and your) motion. This interactive lets you build your own roller coaster and watch the interplay between these two flavors of energy.