Re: Newton's Gravity

Jonathan Thornburg [remove -color to reply] il 03/01/2025 23:18:17 ha
scritto:

Let's analyze a somewhat more general system:  Suppose we have a pair
of masses A and B, and consider the effects of adding a mass C at either
position #1 or position #2.
[Luigi's original question had position #1 = position
of A, position #2 = position of B, mass A = 1000, mass
B = 1, and mass C = 1, but I find it useful to consider
the more generic case.]
>
A+B+C1 and A+B+C2 are *physically different* systems (going from one to
the other involves moving the mass C from position #1 to position #2).
So why should we expect any of the following Newtonian gravitational
effects to be the same between these two *physically different* systems:
* Newtonian gravitational potential U at some test point X
* Newtonian gravitational acceleration "little-g" at some test point X
  (= - gradient of U)
* force between A+C1 and B versus force between A and B+C2
>
In fact, it's easy to see that all three of these "effects" differ...  as
we should expect, because (again) we're comparing *physically different*
systems.

It's true, you convinced me because your reasoning is completely
logical and shareable: we expect anything except that two physically
different systems give the same effects.

But then, why do two extraordinarily different systems like the Earth's
mass (6*10^24kg) generate the force of 90kg-weight on my body (mass
90kg) and my body generates the *same* opposing force of -90kg-weight
on the Earth?

Luigi Fortunati