Re: "Negotiating" a curve. EUREKA?

[Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU>]

John Denker wrote:

> .... I don't see a problem at all.
> ............
> If this analysis isn't good enough, please explain
> why not.  Please be as specific as possible.

The question was presented like this. The pedal-less tricycle,
at time zero, has its back wheels on the x axis and its front
wheel on the y axis. At that moment the planes of all three
wheels were parallel to the y axis and the tricycle travels
along the y axis (north) with some speed. The net force, is
the vector sum of three equal "rolling friction forces"; it is
directed toward the south (-y).

Suppose we have two such, nearly identical ,tricycles  under
identical initial conditions. The only difference between them
is that one has the front wheel pointing north while the other
has the front wheel turned west, by some angle. The first
tricycle will be rolling forward (after t=0) while the other
will be turning left. Why?

We agree that with locked wheels both tricycles would be
rolling north and stop after their kinetic energies are
thermalized. The road is horizontal. The rolling motion of
the wheels seems to be an essential factor responsible for
turning. Why?

I know that the so-called "rolling frictional" force is
much smaller that the "sliding frictional" force because the
mechanisms of thermalization are different. But the directions
of both forces are always opposite to the direction of v. Right
or wrong?

Or suppose a tricycle has a rider who changes the orientation
of the front wheel at time zero. Presumably this creates the
centripetal force acting on the center of mass. How? Why
does the direction of the force, with which the road acts on
the front wheel, changes with the orientation of the wheel?
What happens at the three contact areas (between the road
and each wheels) must be part of the answer? Do you agree,
John? What is the answer? Why turning the wheel produces
the negative x component of the net force? Do the westward
directed components also appear at the back wheels?

Yes, only a physics teacher can ask questions like this.
Everybody, including teachers, know why the tricycle turns
Because the front wheel is turned. I can easilly visualize a
student asking "Why bother with an FBD?".
Ludwik Kowalski
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To understand is to find a satisfactory causal  relation which is
objectively correct. To explain is to express that understanding.
To teach is to promote understanding.
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