Re: How can I tell if F is a string or if it is a number?

In article <0995457c-fbad-4159-ba55-bcd21eed0de7@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Pioneer1 <1pioneer1@xxxxxxxxx> wrote:
But it is not true that orbital predictions are made by using
equations that contain force. The force terms are eliminated during
the derivation process:

You're contradicting yourself. Something cannot be "eliminated" unless it is
there in the first place. The calculation *does* use equations that contain
force, and then eliminates them.

In a sense, you are right that if all you care about are orbits, then you get
by with Kepler's laws. But as Patricia Shanahan pointed out, physicists seek
to find laws that govern *all* physical phenomena. It's true that you can
view the world as a disjointed set of isolated, unrelated problems. Today
I'm interested in orbits. Tomorrow I may be interested in airplane design.
The next day I may be interested in semiconductors. I could treat each of
these problems separately, seeking to find the minimum number of assumptions
required to explain each situation, and ignoring the fact that each time I am
inventing a new set of assumptions that has nothing to do with the assumptions
I used yesterday for a different problem.

Alternatively, I could seek a few very general principles that apply in *all*
situations. Most scientists find this approach much more satisfying than the
piecemeal, ad hoc approach above.

Newton's law of gravitation is called the *universal* law of gravitation for
this reason. In a particular problem, say the calculation of a planetary
orbit, you might be able to get away without assuming forces. But to
conclude from that one example that forces are *in general* an unnecessary
theoretical device is to take a very narrow view of science. Before you
discard the notion of force, ask yourself if you could calculate the dynamics
of two colliding galaxies without assuming a theory of gravitation. Kepler's
laws won't be good enough any more. If a simple theory of gravitation
explains both galaxy collision and orbital motion, then it makes sense to
claim that gravity is at work in orbits, even if for some particularly simple
problems you don't need the general theory.
--
Tim Chow tchow-at-alum-dot-mit-dot-edu
The range of our projectiles---even ... the artillery---however great, will
never exceed four of those miles of which as many thousand separate us from
the center of the earth. ---Galileo, Dialogues Concerning Two New Sciences
.

Relevant Pages

  • What is the first law of Universe ?
    ... Now it is consider that Newton / Einstein,s laws ... of gravitation are the first laws of Universe. ... Newton was a clever man therefore when he discovered his ...
    (sci.physics.relativity)
  • Re: [Humour]: People actually said these things
    ... laws, but only barely. ... Despite using circular orbits, Ptolemy's model ... put the Sun at the center of the solar system and not the Earth, ...
    (sci.astro.amateur)
  • Re: LET is on shaky ground - continued
    ... "Martin Hogbin" wrote in message ... Kepler's Laws tell us what happens, ... > Physics does not and cannot answer the question 'why'. ... gravitation alone explains nothing at all about what gravitation actually ...
    (sci.physics.relativity)
  • Re: Why does the earth do a circular motion with the sun.
    ... no perfectly circular orbits in the universe. ... planets from debris in the solar nebula... ... And of course conservation ... By using his universal law of gravitation and his three laws of motion, ...
    (sci.physics)
  • Re: How to test evolution is real?
    ... How do we directly test the laws of gravitation at a distance ... We -assume- the laws of physics ... distances and across a tremendous time span. ...
    (talk.origins)