Nuclear bombs are easy to make, right? Find some uranium, shove in some explosives and—BOOM!—you're quite literally done. Umm, sorry, nope. The big problem in making a nuclear bomb is that you need enriched uranium, and that's actually a real pain in the ass to make. In this video the engineering guy Bill Hammack explains why that's the case—and why it means that, fortunately, nuclear weapons aren't as widespread as you might expect. [YouTube]