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Re: [Phys-L] feeler-dealer, third law, et cetera

I agree with Timothy. If the force on A in question is the sum of forces exerted by each of several different objects then the agent of the force is the compound object (B) that is the collection of those other objects, and the sum of the individual Newton's third law partner simple forces is the Newton's third law partner force being exerted by A on B. There is no logical need for the introduction of new jargon, "compound force" and "simple force". Still I find it appealing and perhaps there is a pedagogical demand for it. Quite often the relevant compound force is the sum of all the forces acting on an object which I typically refer to as the net force. In reflecting on what I call a simple force, I think I usually refer to it as one of the two forces that is part of one interaction. That's quite a mouthful so "simple force" might be better. I'm not sure. I think it's probably better not to increase the amount of jargon that students have to learn.

-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of Folkerts,
Timothy J
Sent: Thursday, December 12, 2013 10:40 AM
To: 'Phys-L@Phys-L.org'
Subject: Re: [Phys-L] feeler-dealer, third law, et cetera

If we adopt that approach, it means force is not a vector.
I say that because according to the definition of vector, the sum of two
vectors must be *A* vector.

In that sense, can't we say that the "single vector force" of 15 N Left = (20 N
Left + 5 N right), has an "equal and opposite single vector force" consisting of
(20 N right + 5 N left)? After all, we can do the vector addition just as well on
the two "reaction forces" as on the two "action forces".

Or put another way ...
* if we are focusing on the force Mr. A applies on the left side of the Crate
only, then there is a N3 counterpart of the Crate pushing back on Mr. A.
* if we are focusing on the force Ms. B applies on the right side of the Crate
only, then there is a N3 counterpart of the Crate pushing back on Ms. B.
* if we are focusing on the NET force Mr. A & Ms. B apply the Crate only,
then there is a N3 counterpart of the Crate pushing back on Mr. A & Ms. B.

F_AC = - F_CA.
F_BC = - F_CB.
F_(A&B)C = - F_C(A&B).

Or we could have F_(universe)C = - F_C(universe)

It seems the notation still works perfectly fine here.

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