Subject: 9.44  Riding with no hands
From: Jobst Brandt <jbrandt@sonic.net>
Date: Tue, 2 May 2006 10:25:45 -0700

Riding no-hands on a bicycle is easier for youngsters who don't worry
about the physics involved or the possibility of failure and falling.
However, doing it is more complex that it might appear.  For an
example of why steering the bicycle by leaning it, we have another
device that is interesting all in itself and that is the air bearing
turntable on which one can stand.

Trying to turn around to face the opposite way on such a frictionless
rotary platform is awkward.  In fact in normal human movement it is
impossible, there being no way of generating the torque required to put
one's body into rotary motion and then to stop when facing the other
way.  Understanding the physics helps, in that one knows that
extending one arm straight out and rotation it in small circles
generated that torque and makes the body rotate.

On the bicycle a similar condition exists in that the bicycle steers
by gyroscopically tilting the front wheel to the direction it is to
steer, and that the bicycle must lean that way to enable traveling in
that circular path.  There is no direct way of leaning the bicycle,
just as there is no way of turning the body on the turntable.
However, moving the hips while the upper body remains upright
furnished that tilt bu using the inertia of the upper body as a
counterforce.