Welcome to the back-of-the-envelope column! A column in the same spirit appeared in this journal, as “The Back of the Envelope” by Purcell1 and as the “Search for Simplicity” by Weisskopf.2 I cannot claim the physics insight of my predecessors, a co-developer of NMR (Purcell, Nobel Prize 1952) and a group leader in the Theoretical Division of the Manhattan Project (Weisskopf). But I am interested in improving how we think about and therefore teach physics, especially through back-of-the-envelope reasoning. I hope that this column will help you to amuse, educate, and inspire your students.

I came to this area of thinking by a roundabout route. Please pardon the personal story, which allows me to thank my teachers. As a graduate student, I heard tales of a famous course, “Order-of-Magnitude Physics,” taught by astrophysicists Sterl Phinney and Peter Goldreich (astrophysics is allegedly the field where the plus/minus appears in...

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