RE: The Rauber Marlow Chronicles

["Richard W. Tarara" <rtarara@saintmarys.edu>]

OK.  Now my problem is, WHAT IS AN INERTIAL FRAME?  If my
example--stationary earth IS NOT an inertial frame (since the claim is
that Gravity doesn't produce a force of several hundred Newtons downward
on me--as I've come to believe), then what is?  Somehow I don't suspect
you'll see a lot of us rushing off to abandon weight as a perfectly good
Newtonian force, but I would like to be clear in my own mind what IS more
correct.  Your students must be a lot smarter than me because I'm having a
very hard time with seeing gravity as a result of a non-inertial frame of
reference.  Do we have to postulate a frame without ANY gravitational
effects to have an inertial frame--that is, must we be very far away from
any massive body?  Somehow I just don't see abandoning weight as a force
in introductory courses.  None of the dynamics we normally work on will
work without it (at least without mental gymnastics way beyond my
students).

Rick 

----------
> From: A. R. Marlow
> > ... but I have trouble with the inertial or near
> inertial > frame analysis where gravity produces an acceleration but no
> force! > > For the sake of argument, lets make it simple and assume the
> earth IS an > inertial frame of reference (stop all rotations).  As I
sit
> here I still > feel the chair pushing me up (could put a scale under me
> and measure the > force--but I won't tell what it reads ;).  However,
I'm
> not > accelerating.  Therefore, as a good Newtonian, I must assume the
net
> > force on me is zero.  
>
> This is not the only conclusion a good Newtonian can come to.  You have
TWO
> options  --  1) the conclusion you chose above; or 2) since you
obviously
> feel a force pressing on you, and yet you are not accelerating, you
could
> come to the good Newtonian conclusion that the frame you are using to
measure
> accelerations is NONINERTIAL, and therefore Newton's laws need not apply

> relative to that frame.  The existence of these two logical options (as 
> Spock would say) should then impel all good Newtonians and other truth 
> seekers to start carefully checking all forces in the vicinity besides
the
> one so obviously being felt, so that they can decide which option is 
> correct.  Use all available means, checking infrared and other spectral
> regions for signs of any posible dissipation from hidden dynamical 
> processes, Etc.  If in the end you decide, really in all honesty there's

> just the one force acting, then you will be impelled in the direction
> Einstein took.  If you were in a local inertial frame, you would not
need
> such a force to keep you from accelerating, and so you must not be using
a
> local inertial frame.