A big idea is one that has no simple or easy answer, and there are four big ideas in this book: motion, energy, matter, and life. The motion of nonliving objects--rolling balls, falling stones, the moon and stars--seems so ordinary and familiar that most people take it for granted. Matter, on the other hand, comes in so many different forms--solids, liquids, gases, metals, nonmetals, living material--that it is hard to imagine anything that all matter has in common. Energy is an idea that is in the news just about every day, yet most people couldn't tell you what the big idea of energy is. And life--what life is--seems mind-boggling and infinitely complicated. How do we bend our brains around it?

Scientists learn by asking questions. And this book, now in paperback, is designed to make young readers stop and think about each of the questions before reading what scientists have learned that answers each question. They'll be able to do simple things to see for themselves, and they will build their own scientific knowledge in the process. By the time they've finished this book, they'll get the big picture of what science is all about.