Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: operational F, m, and a

reply interleaved below.

-----Original Message-----
From: Carl E. Mungan [mailto:mungan@USNA.EDU]
Sent: Wednesday, October 17, 2001 1:27 PM
To: PHYS-L@lists.nau.edu
Subject: Re: operational F, m, and a


Joel wrote:

I still think there is an implicit acceleration measurement occuring,
however. Remember we are dealing with Newton's second law,
which I will
paraphrase as:

In an inertial frame of reference, the sum of the forces
acting on an object
is equal to the objects mass times its acceleration.

That means, in order to use the fish scale to determine
force in the context
of Newton's second law I have to make sure that the tick
mark scale on the
apparatus is a good inertial frame of reference, which means I must
implicitly make another kinematic measurement, namely that
the tick mark
scale has zero acceleration relative to some fiducial
inertial frame of
reference.

If you buy this, it means that equilibrium measurement
determinations of
force involve measurement of acceleration.

Can't we use Newton's first law (N1) to decide if a reference frame
is inertial?

***********
I think Yes!
**********

Specifically, find an object which is isolated (ie, in deep space -
this is a Gedanken experiment). Now look to see whether the object is
accelerating relative to your reference frame.
***********************************
And doing that it precisely what I meant by measuring the tick mark scales
acceleration relative to some fiducial inertial reference frame.
***************************************************

Thus, I take N1 to be a definition (namely of an inertial frame).
With this definition, I now take N2 as an experimental law, in accord
with John D's prescription.
*******************
And I'm arguing that John D's prescription requires that one does exactly
what you suggest in your use of N1. I think you are suggesting the same
thing?
********************
--
Carl E. Mungan, Asst. Prof. of Physics 410-293-6680 (O) -3729 (F)
U.S. Naval Academy, Stop 9C, Annapolis, MD 21402-5026
mungan@usna.edu http://physics.usna.edu/physics/faculty/mungan/