RE: Aluminum Sphere for sale

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Godfrey Loudner" <ggreen@xxxxxxxx>

Circles (spheres) can be considered as a special cases of ellipses
(ellipsoids) respectively. An ellipse has a major axis and minor axis.
If the major axis equals the minor axis, then rotating the circle around
either axes will trace out a sphere. If the major axis is not equal to
the minor axis, then rotating the ellipse around the major axis (minor
axis) will trace out a prolate spheroid (oblate spheroid) respectively.
A prolate spheroid (oblate spheroid) appears like a football (doorknob)
respectively). Spheres, prolate spheroids, and oblate spheroids are the
ONLY cases of ellipsoids which can be obtained by rotating ellipses
around either of their major or minor axes. HOWEVER there are ellipsoids
which CANNOT be obtained by rotating ellipses around their axes. One
example is x^2 + y^2/4 +z^2/9 = 1.

Godfrey Loudner

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Friday, March 17, 2006 8:09 AM
To: tesla@xxxxxxxxxx
Subject: Re: Aluminum Sphere for sale


Original poster: FIFTYGUY@xxxxxxx

In a message dated 3/16/06 8:06:30 PM Eastern Standard Time,
tesla@xxxxxxxxxx writes:

 >Ellipsoid: a 3-dimensional object generated by rotating an ellipse
>about its major or minor axis. All plane sections are ellipses.

     Couldn't a section through an ellipsoid be a circle, if that
circle had as its radii the other ellipse axis?
     And aren't circles a subset of ellipses?

-Phil LaBudde
(Gary could advertise them as "sphere-ish"?)