Two MIT grad students want to install devices in public buildings that generate electricity from footsteps. They want to install a type of floor that will power train stations and other commuter-heavy areas. The problem is that this energy has to come from somewhere - you. This type of floor will depress slightly when you step on it. If the floor moves, then it will require slightly more effort to walk. It's a very mild form of the effect you get when you walk on sand. [MIT]