Re: BEFORE "Negotiating" a curve.

[John Denker <jsd@MONMOUTH.COM>]

At 08:15 PM 11/9/99 -0500, Ludwik Kowalski wrote:
> Yes, I am more comfortable about the curve negoatiation problem
> now than when it presented.

Good.

> the static frictional force has to do with the direction of attempted
> motion rather than with v.

Right.

An ideal wheel has static friction, which is independent of v.  Think about
gears meshing.  There is a force from one gear to the other, but there is
no relative velocity, i.e. no slippage.

> But that phrase a "wheel which offers unlimited resistance to any
> motion other than pure rolling" is not really very different from the
> phrase Brian used, "it rolls because it must".

I don't understand what is your objection here.  I assume you accept the
idea of a force of constraint;  after all, a book is _constrained_ to sit
on top of the table;  the book/table force adjusts itself to match the
weight;  the table offers unlimited resistance to further downward motion
of the book.

Is it that you reject the idea of a constraint between wheel and road?  Is
it because the wheel is moving?  If so, try imagining the wheel as several
dozen little "feet" arranged on spokes.  As the wheel rolls, each foot is
stationary during the time it is in contact with the road.  It generates a
force of constraint, providing "just enough" force to counteract any motion
other than pure rolling.