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Re: L2-"Negotiating" a curve.



Ludwik,
Give me one more shot!
1) The frictional force on the turned front will (in the -v direction) has
a component which produces a torque about the wheel axis.
2) This torque rotationally accelerates the wheel.
3) This rotational acceleration "digs" into the road to push it tangential
to the turned wheel's orientation.
4) The N3 counterpart is a "new" "rolling" friction force of the road on
the wheel in the (turned) forward direction.
5) For this to work you need a frictional road-wheel connection and a
rotating wheel. It won't work on frictionless ice; it won't work with a
locked wheel.

I agree that the details of this phenomenon deserve better
textbook/lecture/contemplation treatment.

Bob

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor

----- Original Message -----
From: Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Thursday, November 04, 1999 6:35 AM
Subject: Re: L2-"Negotiating" a curve.


Bob wrote "The keel effect of the bearing is real". Hmm.
Why don't they say it in textbooks? "The net force at the
C.M. , directed toward the center of path curvature is due
to the kill effect on the bearing". Are we outside the area in
which free body diagrams (FBD) are useful? I do appreciate
Bob's quick reflections very much; the sarcasm is directed
at authors who think that textbook drawings are self-evident.

Yes, the orientation of the front wheel (or two front wheels),
and the fact that the wheels are rotating, are certainly essential.
[The masses of wheels were declared to be negligible to avoid
issues associated with the angular momentum, etc.] The task
is how to explain the "kill effect" with in a FBD. There are
only three external forces (road acting on the rigid platform)
in our simple model. They are applied through turning wheels.

I woke up thinking that wheel were used for more that 5000
years and we are understand them. Sorry for the little Internet
"boxing match" with Bob last night. It did help me a little.
I hope somebody will add more clarity today or tomorrow.
Ludwik Kowalski