Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!ucsd!sdcsvax!ucsdhub!hp-sdd!hplabs!hplabsz!taylor
From: johne@astroatc.UUCP (Jonathan Eckrich)
Newsgroups: comp.society
Subject: Re: Urban legends
Message-ID: <1928@hplabsz.HPL.HP.COM>
Date: 21 Apr 88 23:36:44 GMT
Sender: taylor@hplabsz.HPL.HP.COM
Organization: Astronautics Technology Cntr, Madison, WI
Lines: 32
Approved: taylor@hplabs

Larry Kollar wrote about a CDC disk flipping over a trailer truck...

I don't believe it.  Here's why.

In order for the truck to tip over in a turn due to the spinning disks, there
is only ONE axis in which the disks could be spinning.  That axis would have
to be lateral to the dimensions of the truck.  I am not familiar with the
drives that CDC used but I suspect that they spun on a vertical axis?  The
gyroscopic effect, refered to above, is called precesion.  When a force is
applied to the side of a spinning gyro, the gyro responds as if the force
was actually applied at a position that is 90 deg. in the direction of the
spin.  If the axes of the disks where lateral with respect to the truck, and
the direction of spin was counter clockwise (if viewed from standing to the
left of the truck), then maybe, just maybe, it could happen.  This would
require extremely heavy platters AND very fast rotation, then the driver
would have to make a fairly fast rate of turn.  I'm cross posting this to
rec.aviation, because gyros are commonly used in airplanes.

                            <-------.
                        __________   \  Rotation is counter clockwise.
                      /            \
                     /              \
                    | .              |
                    |/      +        |
                    /\              /
                   /  \     .      /
                  /    ^____|_____^
                 /          |
 Apply force here.          |
                            Gyro responds as if force was applied here.


Jonathan