non-inertial: part II

["Rauber, Joel Phys" <RAUBERJ@mg.sdstate.edu>]

This is a collection of minor points and responses to various item mentioned 
in previous posts.

P. Camp wrote and A Marlow amened the following:

> > ...
> > Forces are interactions between objects and necessarily come in
> > pairs. If you can't identify the other object (and you can't with a
> > centrifugal "force") then it ain't there. It is an effect, not a
> > force.
> > ...
>
> A deep, resounding reverberating YES  --  and we even have a name for
> those mysterious "effects" that appear in noninertial frames;  they
> are called (surprise,surprise) "accelerations."

I have some comments about this definition of force and how it relates to 
the discussion.

1) both folks above agree, as everybody has so far that there is an effect. 
 That is the reason for my not liking the word "fictitious" because there is 
a "real" effect.   In this vain I'm more comfortable with "apparent force"; 
I also like the suggestionof "inertial force", although I understand the 
objection that was raised against that. I still prefer so far the term 
"kinematical force", since the effect is a kinematic effect.

2) I think Marlow must have a contradiction with above definition. On the 
one hand the gravitational force involves an interaction between objects and 
would be called a "real" force.  But on the other hand Marlow's postings 
have told us that the gravitational force is a fictional force and not a 
"real" force. Which is it? It can't be both?

Some speculation on my part:
(Actually this may be only a contradiction, because we have no 
self-consistant theory of quantum-gravity).  An interaction picture of 
forces, I think necessarily brings in an exchange particle viewpoint 
expressing the interaction, and is therefore inherently quantum mechanical.) 
 comments on this anyone?
________________________
Elsewhere (a couple of times) Marlow wrote in two different posts:

> What are these outward
> directed centrifugal "kinematical" forces doing?   The answer is: nothing!
> They don't exist, which is why they cause no effects, which is why they are
> called fictitious.

> just don't confuse everything by renaming
> the accelerations "forces," and then expecting everyone to keep doing
> the mental gymnastics necessary to keep reminding themselves that these
> "forces" don't have the properties that normally define forces.

These fictitious forces to have all the effects and properties I normally 
associate with forces.  (I'm not using the pressure sensor definition of 
force, see (non-inertial: part I)).  Namely, I measure an acceleration 
associated with them, by plotting the position of my object in the frame of 
reference (non-inertial of course, that's where I'm doing the measurements). 
The work-energy theorem seems to work, namely when that force is the only 
force present, the work done by it seems to equal the change in the kinetic 
energy of the object. And from all of this, all of mechanics seems to 
follow. (I hope this last isn't too rash of a statement, but I'm sure it 
will be corrected if need be.)

Its for this reason that the idea of treating these terms as real forces is 
useful.  It in fact allows me to avoid a lot of mental gymnastics to be able 
to simply say that these are forces measured in this particular frame of 
reference, along with all other measurements made in that frame.

Marlow has reminded us that we need a precise definition of Force, I agree 
and would like to know if Marlow has one other than the pressure sensor 
definition that he has given. (I might add that I haven't given a precise 
definition, yet)

> And as long as it is recognized that they will not do any of the things
>  expected of forces in ANY reference frame.  Might as well declare
>  counterfeit money to be real in certain circumstances, and expect not to
>  confuse anybody.

I can't resist responding to this analogy.  Counterfeit money quite often 
spends just as well as real money and therefore is the same as money when it 
spends.

I might add, the price I pay with my viewpoint, is that I have to 
distinguish between two kinds of forces when I transform between inertial 
and non-inertial frames, kinematical forces and physical forces (the ones 
that have a physically identifiable agent responsible for them). But Marlow 
has to distinguish between two kinds of accelerations when he transforms 
between two different frames of reference, those caused by forces and those 
caused by kinematical motion of the non-inertial frame relative to the 
inertial frame.

I think the mental gymnastics is the same for both viewpoints 
(mathematically it amounts to, do I divide by the mass or not on both sides 
of the equation, which is why we agree on the numerical answers to mechanics 
problems, at least when we do the mathematics correctly).  However, 
operationally the viewpoints differ, From measuring the motion of an object 
in a frame of reference (I don't know a priori if its inertial or 
non-inertial) I can't seperate out the acceleration into its two components, 
as Marlow says I must if I'm to understand the motion in terms of forces. My 
viewpoint says I don't need to perform this seperation for my two kinds of 
force in order to understand the relationship between the forces and the 
acceleration of my object, I don't need to because they both contribute to 
the acceleration of the object in the normal manner and therefore the two 
forces get treated on the same footing.  This allows me to not have to 
decide whether or not the measurements were performed in an inertial or in a 
non-inertial frame of reference (I may not know and furthermore may not be 
able to know!!!)

I'll expand on this idea in my third postion "non-inertial: part III"

Thanks for your patience and I hope everyone bothering to read all this is 
enjoying it and that it is helping to sharpen one's thoughts on these 
matters.  It is for me.

Joel Rauber
rauberj@mg.sdstate.edu