[Phys-L] Re: telescope mirrors

[Karl Trappe <trappe@PHYSICS.UTEXAS.EDU>]

Tie a beaker to a lazy susan turntable (or on your rotating stool
apparatus) using string and duct tape.  Partially fill it with water,
spin it and observe.  If you move it off center, the results will not
be symmetric, of course.

For an additional application while you have the apparatus:  secure a
string to the bottom center of the beaker (epoxy a swivel to the
bottom).  tie a cork/styrofoam ball to the string so that it floats
from the bottom.  Next hang a weight on a string from the top (use a
strp of thin aluminum with a hole in it).Set this beaker far off
center and rotate the lazy susan slowly.  The heavy ball will move
outward and the floating ball will move inwardmimmicking the helium
ballon vs the air filled balloon in an accelerating and decelerating
car. Enjoy, Karl


Quoting Anthony Lapinski <anthony_lapinski@PDS.ORG>:

> I'm curious about something. I tell my (high school) astronomy students
> that reflecting telescopes are made by melting glass and then rotating it
> at high speed while the glass solidifies. The result is always a parabolic
> surface. How can one show, in simple terms (no calculus), that the surface
> of a spinning liquid is a parabola? I am also wondering what the "limit"
> would be as the spin rate becomes"very fast." Any help would be much
> appreciated!
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