[net.physics] No such thing as "righting torque"

lew@ihuxr.UUCP (06/02/83)

rocksvax!drdave suggests:

"Calculate the righting torque for a bike wheel at, say, 10 mph
and see how it compares to what is necessary to keep a 150 lb. rider
from falling over."

I don't think there's any such thing as a "righting torque". A gyroscope
responds to a torque in the horizontal plane by precessing, rather
than falling over as might be naively expected. There is no
"righting torque" which counteracts the applied torque.

Suppose you attach a spinning wheel to a frame which allows it to
tip from side to side but not to twist. That is, suppose the axle
is confined to a vertical plane. Now if a torque is applied along
the tipping axis, the wheel is restrained from precessing. The frame
will supply the torque necessary to tip the spin axis downward.
This torque will be perpendicular to the tipping axis, in the
direction of the tipping motion.

The change in angular momentum required by the torque along the tipping
axis will now be supplied by the gross motion of the wheel. The
wheel will tip over just as though it weren't spinning.

The point is that a torque (supplied by the frame) is required to
make the spinning wheel behave as a static object. In the abscence
of such, it will respond to any applied torque by precessing, not
by reacting with a "righting torque".

	Lew Mammel, Jr. ihuxr!lew

dab@iedl02.UUCP (06/13/83)

References: ihuxr.453

Call it whatever you want, but if the reaction (torque) causes the
structure(bicycle) to right itself, or appear to on casual observation,
I think I might be inclined to call it "righting torque" to carry
across the impression of what is happening. WHY PICK NITS. Geese.
         Duff Browne