[Phys-L] Re: rotating stuff (was: telescope mirrors)

[John Denker <jsd@AV8N.COM>]

Karl Trappe wrote:
> 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.

Very nice.  Thanks.

Some tangential remarks and refimements:

> lazy susan turntable

You can still get _record player_ turntables ($10 on ebay) (also
garage sales sometimes) which are absolutely ideal for this demo ...
and for many other demos, including e.g. bouncing a laser off a
tuning fork (or loudspeaker) to draw the acoustic waveform graph on
the wall......

> using string and duct tape

I don't understand how "string" enters into it.

If you really want to get fancy, make an _annulus_ out of light
gauge plywood.  The hole in the middle is just the right size to
hold the beaker.   The outer rim of the annulus is easily duct-taped
to the turntable.
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