In a recent note, Tovar-Hernández and Vaquero1 reviewed an old instrument that illustrates the equatorial deformation of our planet due to its rotation on the north–south axis. Interesting as it is, I only want to stress a pedagogical point. In the referred note, use is made of the concept of “centrifugal force.” Other publications use this terminology as well (see, e.g., Shakerin2).

As is well known, the centrifugal force appears in the context of the use of accelerated frames of reference (see, e.g., Serway and Jewett3), and is part of a class of forces called “fictitious.” As its name indicates, its forced introduction aims to allow Newton’s laws to hold in an accelerated reference frame. True force, instead, appears in an inertial frame, in which Newton’s laws properly hold.

I think that the treatment of these fictitious forces distracts students from the main purpose of...

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