Re: "Negotiating" a curve. EUREKA?

[Bob Sciamanda <trebor@VELOCITY.NET>]

Ludwik,
It occurred to me (while walking the Lake Erie beach) that the wheel
communicates/interacts with the cycle frame, not only through the
horizontal axle bearings, but also through the (almost) vertical steering
column bearings.  In addition, the wheel interacts with you (the rider)
through the handlebar/yoke/steering column system.  In particular, when
you turn the wheel for a left turn, your body will turn in the opposite
direction about the steering column; this forces you toward the center of
curvature and also makes you lean in that direction.  Think on it.
( Note that his is not appealing to any "gyroscopic" effects - what I
describe happens, in principle, even if the wheel is not rotating.)

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: Saturday, November 06, 1999 10:02 AM
Subject: Re: "Negotiating" a curve. EUREKA?


> I think I found another misconception. An attempt to explain
> the centripetal force (on the center of mass of a turning car) in
> terms of an FBD (a free body diagram) is impossible, unless
> the wheels of the car are excluded.
>
> The implied assumption of any FBD is that we are dealing
> with a particle, or with a rigid body. Each turning wheel is
> a rigid object but it is not rigid with respect to the car. After
> excluding the wheels (and the spinning axel, and the inner
> bearing rings, and the balls) we do have a rigid body. The
> forces acting on that body are at the outer rings of the ball
> bearings, as pointed out by Bob, not at the contacts between
> the tires and the road, as stated in so many textbooks.
>
> Saying that the net force acting on the CM of a turning car
> is the vector sum of forces by which the road acts on it is a
> misconception, as far as the FBD is concerned. Indirectly
> yes, directly no. Free body diagrams are limited to directly
> applied forces. Why is this rule ignored when the topic is
> described in textbooks? Do the authors want us to think in
> terms tiny little whees of zero mass? That does not help to
> elimiate conceptual difficulties.
>
> Some may defned textbook writers by saying that every
> thing we teach is only an approcimation. True. But not
> every elimination of a feature is a simplification. Hiding
> an essential element is an error not a simplification. It
> makes the problem more difficult, not mor simple.
>
> Ludwik Kowalski
>
> To understand is to find a satisfactory causal  relation.
> To explain is to express understanding.
> To teach is to promote it.