Re: Newton's 3rd law? was Re: inertial forces (definition)

[John Mallinckrodt <ajmallinckro@CSUPOMONA.EDU>]

> ... Students should be taught to use free object diagrams in both
> equilibrium and non-equilibrium conditions. Far from being gratuitous,
> the centripetal force (that is shown in the diagram ONLY when the object
> is experiencing an acceleration perpendicular to its velocity) is
> necessary to justify and explain the non-uniform motion. The student
> should be taught that the force MUST be there because of the motion; the
> task for the student, then, is to discover the source of this force.

To which I, and I think most of us, shout, "Nonsense."  Yes, one *can*
choose to have students do it this way, but it most certainly is *not*
necessary.  In my experience most physics teachers find this type of
instruction to be a most potent source of confusion.

John Mallinckrodt      mailto:ajm@csupomona.edu
Cal Poly Pomona          http://www.csupomona.edu/~ajm