question-of-the-day answered

[Irene Mogol]

HUH!  Whaddya say?

On Wed, 6 Oct 1999, Kurt Cockrum wrote:

> Rich said:
> >Solution needed.
> >
> >If I have a styrofoam ball one foot in diameter, how can I find the
> >precise location of the opposing poles?
> 
> Suspend the ball from a thread attached to the eye of a needle driven
> into the sphere, and lower it until it touches the ground, plumbob style.
> It will touch at a point more or less antipodal to the point of suspension.
> 
> Another thing to try is to make 2 tangent cones that match at their perpendicular
> bases.  The sphere will be securely contained within the two joined cones.
> Then a line going from the apex of one cone to the other apex will pierce
> a diameter of the sphere.  Try a hot coat-hanger.  A CO2 laser bore-sighted
> along the apices would make the work easy.  This could also be the basis for
> a drill-press fixture that would hold the sphere for drilling.  Rather than the
> cones, an open-air design using tripods that bolt together, caging the sphere,
> might be a workable design.
> 
> Lastly, try a tangent equilateral tetrahedron, with the bottom side missing. 
> Put it over the sphere.  A line from the top vertex to where the sphere touches
> the ground will pass thru the center of the sphere.
> --kurt
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