I purchased this book when my pre-teen granddaughter asked me too many questions I could not easily answer! It is written (and wonderfully illustrated) as a juvenile non-fiction that leaves the adults smiling and interested in how something was built!
We discovered this book (and companion DVD set) a couple of years ago. My now 9-year old, who is a mechanical whiz, absolutely never tires of leafing through it and learning how things work. It often inspires him to create his own thing-a-ma-jigs with Legos.
I highly recommend it to anyone who is interested in machines.