Re: [Phys-l] zeroth order and first order

[John Denker <jsd@av8n.com>]

On 11/08/2007 09:50 AM, Edmiston, Mike wrote:

> ... although this zeroth order versus first order post points out
> that we should carefully determine the major factors,

;-)

> I don't see it as
> applying to anything people have said about tire beads, other than you.

Not said, but IMHO should have been said.  This is a clarification
of my answer to the question Rick Tarara asked 11/06/2007 02:09 PM 
about "two competing models".


> If a flexible rope/wire/string/cable is involved, I view tension as
> directed along the length of this.  

Two responses:
  1) That's true.
  2) If the string is under tension *and* curved, there is a
   also force in the direction of the curvature.  The tension
   (along the string) is the same everywhere in the string,
   while the sideways force per unit length is proportional 
   to the tension *and* proportional to the sharpness of the
   curvature.

> ... the bead is rigidly glued to the rim ...

I bicycle tires there's no glue, and in car tires the "glue"
is not strong enough to do this job.  It's that super-strong
wire in the bead that does the job, due to its tension *and*
curvature.