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Re: [Phys-l] Another tire question

Agreed - I'm afraid I became interested in the importance of the
discussion late in the game and simply forgot the details of your
posting. We obviously share the same mental picture of how the wheel is
suspended - your argument being more detailed and convincing than mine.

Bob at PC

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
bounces@carnot.physics.buffalo.edu] On Behalf Of Jeffrey Schnick
Sent: Friday, November 09, 2007 1:14 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] Another tire question

Bob,

Because you say essentially the same thing I said before, except that
what I call the (wheel+bead) you call the wheel, your comments
indicate
that you did not get my first post on this topic. Did you get that
post? If not, I am definitely "talking" past you. The message read:

Here's my take on the situation. I think it's good to first order.

Before you put the tire on the wheel, the radius of each bead is
smaller
that the radius of the part of the rim on which it is designed to
reside. When you put the tire on the wheel, assuming the bead is in
its
ultimate resting place on the wheel, the bead will be stretched.
Assuming no bunching, there will be uniform tension in the bead. That
tension will remain uniform at one and the same value throughout the
rest of this discussion because the length of the bead will not change
and the tension in any segment of the bead is determined by its length
and its spring constant.

Considering forces only in the plane of the circle formed by the bead,
the wheel will be exerting a radially outward force-per-length loading
on the bead. That loading times the length of any infinitesimal
segment
of the bead is the "in the plane of the circle formed by the bead"
component of the normal force on that segment of the bead. The
Newton's
3rd law partner to this loading is a radially inward directed loading
exerted on the wheel by the bead. It pushes inward on the surface of
the wheel. The bead can only push on the wheel. The bead is not
trapped.