Re: BEFORE "Negotiating" a curve.

[Bob Sciamanda <trebor@VELOCITY.NET>]

John Denker wrote to Ludwik:
> . . .There is a notion of "ideal wheel" which suffices to
> answer your questions about negotiating a turn.  I say again an ideal
wheel
> offers unlimited resistance to any motion other than pure rolling.  If
this
> model isn't good enough, please explain why not.  . . .

Ludwik,
Forgive me for presuming, but I think you may be missing the point that
the force of "unlimited resistance to any motion other than pure
rolling" is transmitted (through the bearing) to the frame.  This gives
rise to a large transverse force of static friction.

In sum, the frictional road force on the turned wheel is resolved into
tangential and transverse components by the bearing.  The tangential
component affects rolling motion; the transverse component
(perpendicular to the plane of the turned wheel) is transmitted, through
the bearing, to the frame and provides a "sideways", turning force.

I think you are also misled in the assertion that the frictional force
is in the -v direction.  That may be true of kinetic friction, but
static friction is in the direction opposite to any ATTEMPTED motion.
Here we have a combination of both, along with rolling friction.  It is
the attempted, directly forward motion that gives rise to a large static
frictional force transverse to the plane of the turned wheel.  In a FBD,
all of these external forces are shown acting at the CM, to illustrate
the LHS of F_ex=mA_cm .
Hope this helps.

Bob

Bob Sciamanda
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor