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Re: [Phys-l] interaction



On Aug 3, 2007, at 10:30 AM, LaMontagne, Bob wrote:

May I pose a question that a student might ask if presented with this interaction approach? Consider the sun and one of the planets. In the usual approach to fields at the introductory level, we consider the planet to interact not directly with the sun, but rather with the local gravitational field it is imbedded in. In the sense of interactions obeying NTN 3rd, why is the force on the sun toward the planet considered the other interaction force? The planets are interacting with the fields, not interacting with each other directly (action at a distance.) I think this interaction approach gets a little fuzzy here.

Two people pulling a broomstick in opposite directions do interact with each other, indirectly. But the sun-earth interaction involves two fields. Sun creates one field and earth creates another field. A field created by an object acts on other objects only; not on its own source. The field created by sun at earth location is much larger than the field created by earth at sun location. But forces are identical due to differences between masses. I tend to agree with Bob's observation about fuzziness.
_______________________________________________________
Ludwik Kowalski, a retired physicist
5 Horizon Road, apt. 2702, Fort Lee, NJ, 07024, USA
Also an amateur journalist at http://csam.montclair.edu/~kowalski/cf/