Learning how science and the world work is rarely is as much fun as in this book from Randall Munroe, the creator of the XKCD comic. It's good for kids and adults.

For anyone who grew up imagining that the floor was lava or wondering what would happen if gravity reversed, good news: Randall Munroe's new book -- "What If?: Serious Scientific Answers to Absurd Hypothetical Questions" -- started arriving [today].