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Re: [Phys-L] ? FCI --> momentum flow



John Denker:

I like the "carried by" wording. It is what I meant by "is shepherded by" but it is a better choice of wording. Your response to my last post <http://www.phys-l.org/archives/2013/10_2013/msg00084.html> indicates to me that you did not read the last paragraph of that post. I am aware that there are other possibilities such as lack of time or interest, but just in case you simply didn't see it, here it is again, prefaced with the line from you to which I was responding:

If that isn't the desired answer, please re-ask and/or clarify the question.
Hopefully I have done that, rather than having muddied it further. Please note that I don't think the issue I am raising in my question in any way shoots down the model. I think the non-local conservation option mentioned above is none other than the action-at-a-distance model. As regards models that preserve local conservation of momentum, I think that downward momentum can and is indeed shepherded upward right through the bottom book to the middle book in both a field model and a particle exchange model. I think we can also get around the issue by saying that there is no upward flow of downward momentum to the book but rather that the downward flow of downward momentum, say from the top book to the middle book, corresponds to an unbalanced ever-increasing amount of upward momentum in the top book which we don't see because we are in an accelerated reference frame. Fix an accelerometer to that top book and you will see that it is registering an upward acceleration of 9.8m/s^2. I think that the momentum flow model is powerful and useful but I am still trying to get a handle on it. Thanks for bringing this topic up and thanks for your thoughtful responses to the questions. I really, really like the idea of giving people two ways of looking at interactions (pushing on something makes it so that that something is accelerating, and pouring momentum into something makes it so that that something's momentum is changing). I think you are setting up a straw man when you say that some people say that it is too simple. And I think you are shooting that straw man down in an incorrect manner when you sat that yes, it is simple, but that's because the underlying physics is simple. I think it is complicated.


-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of John Denker
Sent: Monday, October 21, 2013 8:59 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] ? FCI --> momentum flow
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In the immortal words of Richard Nixon: We could do that, but it would be
wrong.
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