One of the reasons many of us make things is to understand them, to understand not only how the parts and pieces fit together and how they accomplish what they accomplish once assembled but also the working principles behind the assembly. PublicResourceOrg offers a terrific library of old films, mostly from the Department of Defense, that explain a wide variety of processes and principles. The list is impressive and includes things like: basic amplifiers, DC motors, AC motors, resistance, and capacitors just within the electrical category. While the example technologies are dated, the visualizations are, to my eye, just as good as anything we could offer today. Perhaps they are better, for the limitations of the era’s media forced the presenters to focus on what matters most and not simply what could be included. (Because we can is a principle familiar to many of us, but I bet many of us would also admit that sometimes that way leads to distraction or, at least, digression.) The link takes you to a kind of master page of all the Youtube playlists Public Resources has assembled.