Re: centrifugal force (cont)

["John S. Denker" <jsd@MONMOUTH.COM>]

> > I'd like to hear a fictitious dialogue between a professor and
> > a thoughtful student where the professor is explaining the
> > difference in viewpoints we are discussing here.

Ludwik Kowalski wrote:

> IS THIS GOOD ENOUGH?
>
> Professor:
> Centrifugal something is not a force because forces arise
> from *interactions*.  A force is defined as a measure of
> strength of interaction between two objects.

1) This is not necessarily a wise definition of
force.  It reduces the third law to a tautology.
IMHO it would be better to define force on
an object-by-object basis, and then assert
a non-tautological third law that requires
the force on this object to be balanced by
the force on some other object.

There are many cases where it is convenient
to observe a force on a single object without
obsessing on what other object(s) are involved
in the momentum-conservation.> Student:

2) Nitpicking the definition of force is irrelevant
anyway, because the centrifugal field is not a
force field, it is an acceleration field, just
like gravity.

> But according to an old book I any measurable push or pull
> is a force. Centrifugal something, for example, on a bead
> mounted on a horizontally rotating rod, can be measured
> and it should be called a force. What is wrong with this?
>
> Professor:
> Is what you are measuring a push or a pull?
>
> Student:
> Hmm, it is neither push nor pull.

Whaaat?  If you attach to "this" side of the bead
it's a pull.  If you attach to the other side of the
bead it's a push.  You can't make centrifugity unreal
by playing word games with the definition of "push" and
"pull".

Centrifugity is equally as real as gravity.

> The N3 law tells us that forces always appear in pairs.
> You seem to be saying that Newton was wrong; the
> centrifugal force on a rotating platform is acting on an
> object but that object does not act on anything else with
> an equal and opposite force.

Nobody is saying that.  Conservation of momentum
works just fine in rotating frames.  Just because
some folks don't know how to do physics in a
rotating frame doesn't mean it can't be done.