Re: Newton's first law

[Bob Sciamanda <trebor@VELOCITY.NET>]

The first law cannot be used in isolation to find inertial frames.  The
left hand side of the second law must be filled in before one can identify
a force free situation.  When Isaac gave us F=ma he was proposing that we
could (at least in principle) find an inertial frame AND a set of force
laws which would allow us to make sense out of observed accelerations
through the paradigm F=ma.  He (successfully) applied this to the (then
known) solar system by invoking the universal gravitational force among
all masses.

Isaac's farthest reaching contribution was the invention (definition) of a
useful concept of FORCE.  This concept is defined by the sum of ALL THREE
of "Newton's Laws".  The first "law" is saying that this force concept is
only operationally valid for a non-accelerating observer.

Remember that Isaac thought in terms of absolute space, time and motion.
In fact, he probably began by assuming that his physics would only be
valid for an observer at absolute rest.  The existence of a whole class
(infinite in number) of valid inertial frames was a surprise conclusion,
not an assumption.  (It was also a disappointment because it shattered the
hope of measuring the earth's absolute velocity by mechanical
experiments - the Michelson Morley experiment was an ingenious attempt to
circumvent this limitation by using optical (E&M) effects.)

Bob

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor

----- Original Message -----
From: "Carl E. Mungan" <mungan@USNA.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Wednesday, September 13, 2000 10:48 AM
Subject: Newton's first law


> I'm interested in how folks introduce Newton's first law (N1) to
> their classes. . . .
> --
> Dr. Carl E. Mungan, Asst. Prof. of Physics   410-293-6680 (O) -3729 (F)
> U.S. Naval Academy, Annapolis, MD 21402-5026     mailto:mungan@usna.edu
>              http://physics.usna.edu/physics/faculty/mungan/