Comments on the Culture of the Force

Frank Wilczek’s column exposes a delicate point in physics teaching. Good teachers avoid implanting misconceptions to be overwritten later. Yet Newtonian mechanics courses do just that! During 20 years teaching I’ve maintained that Newton’s three laws are neither good laws nor independent. Students enjoy hearing the first law is just as circular as it seems. Textbook apologies that falsely limit physics to inertial frames contradict later teaching that physics can be used in any coordinates. Perhaps the first law was just a political device to start discussion, and to divide Newton’s detractors. The third law is necessary for beginning physics of ropes and pulleys, but is wrong as “principle”: Momentum conservation via translational symmetry has myriad solutions. The second law is okay, but it is indefensible to promote Newton’s emphasis on “force” as primary, only later to revise it with Hamilton’s equations of greater scope. Eventually I evolved a refreshing approach to non-calculus physics with energy and conservation laws as primary, and it works well.

Students happily accept that Newton sometimes guessed wrong. A timid teaching culture and careless textbook writing create the intellectual inertia Wilczek observes. Good physics teachers need to demonstrate critical thinking, distribute their own notes, and have the courage not to brainlessly repeat what is written in the book.