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

Pioneer1 wrote:
....
I understand this. But instead of considering Newton's laws as a
general framework, I'm just looking at the specific assumption of
force in the computation of orbital motion. The assumption is not
justified, as far as I understand it, because we assume it but then we
eliminate it, and compute orbits without it. If it's not used why
assume it?
....

That misses the key point of Newtonian physics, and indeed of much of
science. The main objective of the game is to find simple theories that
explain and predict a lot of observations. By that standard, Newtonian
physics is one of the most spectacularly successful theories ever developed.

You might be able to build a reasonably simple forceless theory for
orbital motion, but it would probably be at least as complex as
Newtonian physics and be much less useful for even closely related
questions, such as deciding how heavy components of a satellite need to
be to survive accelerations during launch.

Patricia
.