Re: [Phys-l] pseudo-force

["Jeffrey Schnick" <JSchnick@Anselm.Edu>]

John Denker wrote:

> ...
> I'm optimistic that we can sort out this mess.  After all,
> motion is lawful, even motion in accelerated frames.  We
> know the equations of motion; we're just fussing with how
> to interpret and/or explain the various terms in the
> equations.

Mechanical engineers have to deal with this sort of thing.  Suppose you
have a part that you need to have accelerate along a rail (that is not
necessarily straight) that is rigidly attached to a table that is
rotating about an axis with a fixed orientation relative to the lab
frame, an axis that is accelerating relative to the lab frame.  What
tangential (to the rail) force is required to drive the part along the
rail with the desired acceleration when it has a specified velocity?
What normal force must the rail exert on the part?

As far as I can tell from my study of his sophomore level textbook
_Engineering Mechanics Dynamics_, Sixth Edition, 1992; R. C. Hibbeler
never mentions a pseudo force, fictional force, inertial (or
non-inertial) force, or a centrifugal force.  Rather (in Section 20.4
Relative-Motion Analysis Using Translating and Rotating Axes), he
develops kinematical relationships that will allow you, given the
velocity and acceleration of the part (in the example above) relative to
the table, to determine the (velocity and) acceleration relative to the
lab.  Then, to the extent that you can treat the lab frame as an
inertial reference frame, you can apply Newton's 2nd law to determine
the net force needed to cause that acceleration.

Jeff Schnick