Book excerpt: From an award-winning teacher, “a delightful and instructive accessory to an introductory physics course” (Physics World). Physicists use “back-of-the-envelope” estimates to check whether or not an idea could possibly be right. In many cases, the approximate solution is all that is needed. This compilation of 101 examples of back-of-the-envelope calculations celebrates a quantitative approach to solving physics problems. Drawing on a lifetime of physics research and nearly three decades as the editor of The Physics Teacher, Clifford Swartz—a winner of two awards from the American Association of Physics Teachers—provides simple, approximate solutions to physics problems that span a broad range of topics. What note do you get when you blow across the top of a Coke bottle? Could you lose weight on a diet of ice cubes? How can a fakir lie on a bed of nails without getting hurt? Does draining water in the northern hemisphere really swirl in a different direction than its counterpart below the equator? In each case, only a few lines of arithmetic and a few natural constants solve a problem to within a few percent. Covering such subjects as astronomy, magnetism, optics, sound, heat, mechanics, waves, and electricity, this book provides a rich source of material for teachers and anyone interested in the physics of everyday life. “This is a book that will help make the study of physics fun and relevant.” —Mark P. Silverman, author of Waves and Grains: Reflections on Light and Learning