Re: [Phys-l] Equations (causal relationship)

[John Denker <jsd@av8n.com>]

Brian McInnes wrote:

> (1) Forces are external to a particle.
> I'd rather think of a force as an interaction between a particle and  
> its environment but, in the context, of this discussion, we all seem  
> to be looking at the particle (or the body).
> There is a physical basis to this assertion,

Proof by Bold Assertion.  You say there is a physical basis, but you
do not say what the physical basis is.

I know of no experimental or theoretical basis for saying a force is
more "external" than an acceleration.  I know of no equation for
quantifying the "externalness" of a vector.

> (2) There can be many (or no) forces acting on the particle.
> There is a physical basis to this assertion.

PbBA.

I see no reason to disinguish force from acceleration on this basis.

> (3)  Acceleration is an attribute of a particle.
> Again, here is a physical basis to this assertion.

PbBA.

I know of no equation that quantifies the "attributeness" of a vector.

> (4)  In a given reference frame the acceleration of a particle has a  
> single value.
> And yet again, there is a physical basis to this assertion.

PbBA.

I concede that given three contributions to the acceleration, only
the total acceleration (a1+a2+a3) is significant;  to be precise, it
is a _sufficient statistic_ for calculating the motion ... but in the
same breath I point out that only the total force (F1+F2+F3) [aka net
force] is significant.

The laws of physics do not distinguish between force and acceleration
on this basis.

This is not a technicality.  If you permit me to pick apart the force
I can also pick apart the acceleration;  if you require me to lump
the accelerations together I will insist on lumping the forces together.
I must insist on consistency.

> So, let me know which one or more of these 4 assertions you would  
> like me to spell out.

Four pieces of non-evidence do not add up to one piece of evidence.