Back-of-the-Envelope Physics

Rating:
Summary: An entertaining book on real world physics
Review: This book is a breath of fresh air. Contrary to some books where abstract theories are discussed at length but whose connection with reality remains elusive, this book contains calculations on phenomena in the real and currently observable world. Approximations, i.e., back-of-the-envelope calculations, are performed for a great variety of physics topics that makes for truly fascinating reading. The math is mostly high school level with a small dash of calculus in a few cases. The text is clear and engaging and complements the calculations very well. The reason that I am giving it four stars instead of five is that there are several typos in the calculations and the units are not always carried through, i.e., numbers are often presented dimensionless when they are not. Otherwise, a fascinating read that I heartily recommend.

Rating:
Summary: Physics problems solved to a first approximation
Review: To my knowledge, the most celebrated instance of a back-of-the-envelope computation occurred when the United States detonated the first nuclear weapon. Physicist Enrico Fermi tossed some papers into the air and measured how far the blast wind took them. From this, he performed a rough computation on the power of the bomb that was very close to the measurements taken by the more sensitive instruments at ground zero. In fact, this may have been the origin of the term, although I have no evidence either way.
The examples in this book are all simple strategies that can be used to perform complex computations in physics. In all cases, the goal is to get a ballpark figure rather than an extremely accurate one, so there are many simplifying assumptions. All areas of physics are covered, starting with force and pressure and going all the way through particles and quanta. While all of the computations are applied algebra and so can be understood by people with those skills, understanding the formulas requires knowledge of the physical principles. Therefore, one of the most sensible uses for this book would be as a source for physics problems whose solutions require very little equipment.
For example, how do you weigh a car? The solution is to make sure the air pressure is the same in all tires and then measure the surface area where those tires are in contact with the road. If the rigidity of the rubber is ignored, the multiplication of pressure times surface area will be the approximate weight. I enjoyed these problems and am sure that students would find them interesting and fun.