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Re: [Phys-l] bound vectors ... or not



I'm confused about this discussion too...

2) I think we all agree that in many situations when dealing
with a force, we need the idea of direction-and-magnitude of
the force and also the idea of point-of-application .....

Agreed. And to your point about viewing the angular momentum L as (d/dt) of the torque T, I would expect what follows below to apply to both L = r x p and T = r x F.


The question is simply whether we want to express those two
things using one "vector" (i.e. a so-called bound vector)
or using two vectors (i.e. plain old vectors, aka free
vectors).

Eh? Based on the wiki article you cited, a bound vector "possesses a definite initial point and terminal point." By this simple reading, both r and F qualify. Specifically, T is context-sensitive... I can make it zero simply by defining the vector r appropriately wrt F, which definitely qualifies r as a bound vector. Likewise F: changing the direction and location (initial and terminal points) of F will change the torque for a specified r. The torque vector T, on the other hand, would suddenly seem to qualify as the free vector. Once r and F are specified completely, each with their initial and terminal points, the vector T (direction determined by right-hand rule, magnitude by rFsin(theta)), is more like a disembodied entity, aka free vector. Likewise the discussion for L = r x p: {r,p} = bound, L = free.


My reading of the math and physics literature going back 50+
years is that vector means free vector exclusively, so that
a so-called "bound vector" is not really a vector at all, but
rather a pair of vectors, like two persons inside a horse
costume.

Are you saying that you would view r x F as one bound vector consisting of a pair of free vectors r and F? By my reading, it is exactly the opposite. However, back to my original admission of confusion - what purpose is there to begin with to define bound and free? I [either sheepishly or sadly, not sure which] never heard of a bound vector until this discussion. Does it satisfy someone's need to formalize this stuff to the nth degree, or does it serve a useful purpose?


I'm sure Banesh Hoffmann didn't write about bound vectors on
a whim.

I don't have Hoffmann's book so I can't comment. As to the bivector, I obviously have access to your Clifford pages now that your server is back up, but can't say I've read through it enough to answer your bivector hypothesis.


Stefan Jeglinski