How Do Seesaws Go Up and Down?: A Book about Simple Machines

"Have you ever wondered how seesaws go up and down or how screws stay secure in walls? In the How Do series, readers are welcome to guess along with the rest of us--and then explore the science behind the right answers. Beginning concepts of mechanical engineering including levers, wedges, inclined planes, and more are learned through diagrams, photos, and informative and engaging text"--Publisher's description.