Re: [Phys-l] bicycle stability (yes, again)

[John Denker <jsd@av8n.com>]

Richard L. Bowman wrote:

> I think we might have confused the fine points of stability with the 
> major points, and will still cite and explain to my students that 
> angular momentum conservation is the major component in keeping a 
> bicycle balanced with steering techniques and geometric design 
> playing critical roles in actual bicycling.

If we are going to discuss the fine points, please let's first clean
up the terminology.

  1) In my book, balance is synonymous with equilibrium.

  2) /Stability/ is a markedly different concept from equilibrium.

Generally one must discuss equilibrum first;  stability concerns
the response to departures from equilibrium.  More generally one
must discuss not just equilibrium and stability but also /damping/.
For additional discussion of the basic concepts, see
  http://www.av8n.com/how/htm/equilib.html

Also:  I believe the original question asked about actual bicycling.

However, because there are feedback loops involved, it certainly makes
sense to investigate not just the closed-loop behavior, but also the
open-loop behavior (dummy rider aka paralyzed rider).  Beware that the
*no-rider* case is in some ways uninformative or even misleading with
respect to the real-rider and dummy-rider situations.  It also may
be interesting to discuss the case where the rider closes the loop
using only weight-shift techniques, without touching the handlebars.

In any case, if people are going to discuss something other than the
normal hands-on closed-loop actual-bicycling situation, it would be
nice if they would clearly specify the system they are talking about.

=====================

Folks who are interested in the alleged significance of angular
momentum are invited to compare a bicycle to a two-wheel
kick scooter.  The latter has orders of magnitude less angular
momentum ... yet in the normal closed-loop riding situation, it
exhibits many of the same basic behaviors as the former.