DescriptionView full lesson: http://ed.ted.com/lessons/why-don-t-p...Perpetual motion machines — devices that can do work indefinitely without any external energy source — have captured many inventors’ imaginations because they could totally transform our relationship with energy. There’s just one problem: they don’t work. Why not? Netta Schramm describes the pitfalls of perpetual motion machines. Lesson by Netta Schramm, animation by TED-Ed.