Really that entire site is wonderful, and quite varied. But note that it's largely not solid reference material (aside from perhaps portions of the electricity

Really that entire site is wonderful, and quite varied. But note that it's largely not solid reference material (aside from perhaps portions of the electricity stuff), it's more fun and interesting things to play with / think about, that often require some knowledge of science to understand or make work or show why they can't work. And a little bit of crackpottery, some of which is even explicitly labeled as such.