The main point is that if, when going straight, you start falling over,
the wheel can turn into the direction in which you are falling thereby
putting you into a rotating reference frame in which the centrifugal
force provides a torque about the line through the two tire/road contact
points that counteracts the torque provided by the earth's gravitational
force about the same line. It doesn't matter whether you have to turn
the wheel or it turns by itself except that, at slow speeds, you are
better at turning it just the right amount. The stability when rolling
comes from the fact that there is a rotating reference frame that you
can enter into by a simple turn of the wheel about the steering axis.
The gyroscopic effect fine tunes this stability to the extent that the
wheel turns the right way automatically so you can ride the bike with no
hands.
Jeff Schnick
-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Richard
L. Bowman
Sent: Wednesday, August 30, 2006 1:35 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] bicycle stability (yes, again)
I forget if the following Am. J. of Phys. article has been referenced in
this thread or not.
Daniel Kirshner, "Some nonexplanations of bicycle stability," Am. J.
Phys., 48, 36-38 (1980).
He explores contributions to stability arising from steering design.
Kirshner is responding to Jones's assertion in a 1970 Physic Today
article that nongyroscopic effects are most important. Kirshner states,
"We sought to verify that such nongyroscopic theories could account for
bicycle self-stability. We found they could not."
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.
Richard Bowman
Prof. of Physics
Bridgewater College