Re: steering

[Brian Whatcott <betwys1@SBCGLOBAL.NET>]

At 08:13 AM 11/23/2003, you wrote:
///
> A single large and heavy tire is cut to make a vertical
> groove. It is wide enough for me sit in it, at the bottom.
> The tire is at rest on an icy road supporting it; that road
> is only slightly wider that the tire. The snow around the
> road allows me to use ski poles, when I want.
>
> 1) What should I do to reorient the tire left-wise
> without moving our center of mass?
///

There is a way not involving ski poles. It goes like this.
If I walk forwards on the interior of the giant tire, it
begins to roll forwards. If I now combine walking forwards
while spinning  to the right on every other step, the reaction
steers the tire to the left.




> 4) Sitting on my tricycle without pedals I ask
> somebody to push me. I am riding along a
> straight line at a nearly constant speed. Then
> I rotate the fork and the tricycle turns left. Why
> does this happen? Because the right back
> wheel is pushing the road backward, like if
> it were the end of my ski pole. I am applying
> this force by reorienting the front wheel. At the
> same the left back wheel is pushing the road
> forward, as if it were a ski pole. Reorienting
> the front wheel (working against kinetic friction)
> is like working through ski poles. In this situation,
> however, the vehicle has three wheels and it
> rotates around the vertical axis passing through
> its center of mass.

///

> Is my qualitative explanation acceptable to you?

No.

> If not then why not? Please give an acceptable
> explanation, if you have time. Focus on #4.
> Ludwik Kowalski


I try not to avoid an effect which is omnipresent with
 massive items in motion, such as a tricycle.
That is: when in motion, they continue on a straight line,
unless forcibly reoriented.
 This is inertia - or linear momentum.

I am coasting, legs up on a tricycle.
I turn the handle bar a few degrees left.
The front fork begins moving leftwards.
Why?
 The fork rim and tire have turned a few degrees left.
 The tire now attempts to continue forwards (the inertia effect
 mentioned above.) This creates a frictional force.
The  component of this frictional force
perpendicular to the rim is high  (it's called scrubbing - it's
the one that can reduce a car tire to a smooth surface in one
thousand miles or less.) The component of this force in the
direction of the rim is still low (It's called rolling resistance,
and allows a reasonable production car tire to survive for
 sixty thousand miles or so.)
The resultant velocity is within a few degrees of
the direction of the rim (this is the so-called 'slip-angle' of a
turning car tire) and the tire is providing a turning force on the
tricycle.

 As soon as the frame starts to turn, the rear wheels,
 though still still undriven, experience a similar side force and
the tires 'slip' at a few degrees outwards.,



Brian Whatcott    Altus OK    Eureka!