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

[Paul Lulai <plulai@stanthony.k12.mn.us>]

a few seconds to clarify the end of my interactions comment.

We discuss that /Forces are interactions/.  N3L pairs are the two halves to an interaction. My feet and the floor interact.  One half is my feet pushing on the floor.  The other half is the floor pushing on my feet.

If one includes a summation of forces, then there are violations of n3l all over the place and it should be abandoned.  
I think abandoning it is a bit silly.  I think it works when looking at the 2 halves of an interaction.  

The riddle was nice.  

 

-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of jbellina
Sent: Thursday, December 12, 2013 8:07 AM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] feeler-dealer, third law, et cetera

Seems to me there is logical error in your analysis.  The claim in Newton's third is not about "net force" but about individual interactions between objects.  Net force is a mathematical construct and thus does not necessarily have physical sense in the way that individual ones do.  It seems to me to be a false generalization to say that because individual forces follow Newton's third, that all constructed forces must also.

joe

Joseph J. Bellina, Jr. Ph.D.
Emeritus Professor of Physics
Co-Director
Northern Indiana Science, Mathematics, and Engineering Collaborative
574-276-8294
inquirybellina@comcast.net


On Dec 12, 2013, at 7:12 AM, John Denker wrote:

> > Net force isnt *A* force it is a sum of forces.
> > An account balance is neither a debt nor a deposit.
>
> 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.  This is called /closure/.  This 
> requirement is so fundamental that it sometimes goes without saying 
> when people are listing the vector-space axioms:
>  http://en.wikipedia.org/wiki/Vector_space#Definition

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