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Re: sreering



On 11/21/2003 01:34 AM, Ludwik Kowalski wrote:
>
> A railroad car turns because rails turn. This can be
> viewed as a kind of steering. Potential energy would
> have to increase to derail such car.

Yes.

> This, however, can not be said about steering a car
> along a curving flat road. Here friction is essential.

Necessary but not sufficient, and nowhere near being
the interesting part of the story.
There has to be "enough" friction, but over a wide
range more friction or less friction at the tire/road
interface won't change the steering behavior.

I say again: scrutinizing the friction will *not*
lead to an understanding of steering.

I say again: you have to understand the axle and
bearing in the middle of the wheel.



The thought about the railroad is apt and useful.
The wheel has a flange that is to a first approximation
cone-like ... I'm calling attention to the fact that
the wheel has a smaller diameter zone on the outboard
side and a larger-diameter zone (the flange) on the
inboard side.

| | | |
| | | |
|_ | | _|
R|_| |_|R (R = rail)
R R

The bicycle exploits the same physics, BUT IT HAPPENS
INSIDE THE BEARING, nowhere near the tire/road interface.
The bearings are distinctly conical. It's like the
railroad wheel+rail, all rolled up into a package.

I'd tell you to take one apart but it is a bit of
a bother to get it put back together properly.
Perhaps you could go to the bike shop and ask
Wilbur or Orville to give you a scrap one. Similarly
an auto shop should be able to give you scrap
bearings from a car wheel. They are distinctly
conical.

Here's a picture that shows part of the story.
http://static.howstuffworks.com/gif/bearing-wheel.jpg

To repeat: The bearing can roll freely in one direction
for the same reason a railcar can roll down the rails.
The bearing develops a tremennndous force if you try
to push it in the cross direction, for much the same
reason that the flange on a railcar wheel develops
a force if you push it sideways. The bearing actually
carries the idea to perfection; you can't "derail"
it.