Re: centrifugal force

[LUDWIK KOWALSKI <KOWALSKIL@alpha.montclair.edu>]

                        Referring to this:

> > The law of inertia states that "if the net force acting on a body is
> > zero then the velocity remains constant". I do not see why this should 
> > not be applicable in the rotating frame of reference. If the bead on 
> > [or inside of] the rotaing straw does not accelerate then the net 
> > force acting on it is zero.

         Bob Sciamanda <trebor@velocity.net> wrote (yesterday):

> ... The bead won't stay put on the rotating straw unless you provide 
> an unbalanced force (glue). ...

Yes. The "glue" can be due to an electric battery (the bead is charged),
to a magnet (the bead is made from iron), to wind blowing toward the 
center (in this part of the spinning habitate), to the contact with the
floor (at the end of the straw), to spring (or muscles of a living 
creature), etc. etc. No different from what is needed to eliminate 
gravitational acceleration.

> > A frame of reference is inertial if it does not accelerate with 
> > respect to a frame which is already known to be inertial [distant 
> > stars as used by Newton]. What is wrong with this operational 
> > definition?

> Nothing!  This is a frame in which F=ma seems to work; but this is 
> not self evident a priori.  

Yes, nothing is obvious a priori. Answering the same question Leigh 
Palmer <palmer@sfu.ca> wrote (also last night):

> It requires that an experiment be done which refers to the world
> outside the frame. You ought to be able to determine whether a
> frame is inertial or not without referring to the outside world.
> Do you think the fixed stars affect the experiment you do in
> your laboratoty? To the extent that they do not, the decision
> about whether a frame is inertial or not should be within the
> capability of the experimenter to determine wholly within the
> laboratory.

And distant stars are part of that laboratory. Who knows how physics
would developed without them?

This interesting topic is not a "bag of warms". It is worth discussing,
it is worth presenting to students. How else can we make physics 
interesting at all levels of teaching? The concept of the centrifugal 
force is not always useful. But it is NOT a heretical concept. Some 
problems, such as prolate deformation of a rotating sphere, are easier 
to explain with centrifugal forces than without them. And the bead in 
a spinning habitate. "Real to you but 'fictitious' to me" is part of 
our physics.
                                           Ludwik Kowalski