Re: Bobs for Lenz's law apparatus

[brian whatcott <inet@INTELLISYS.NET>]

I took down from the shelf a sample of the Neodymium Iron Boron
 magnets rescued from disk drives which are exquisitely
powerful for their size. An 11 gm magnet will lift 15kg etc

The kidney shaped magnet, though difficult to
measure with a stainless steel dial calliper on account of
its sticking to the jaws, appears suitable for imbedding in
a resin cylinder of the size you want, perhaps of optically
clear casting resin?

 This would  be a reasonably low priced replacement.
(eBay keywords: 'powerful magnet' - about 50 cents to $3)

At 11:21 7/7/01 -0500, Paul O Johnson wrote:

> The Science Place has set up an exhibit based on the Lenz's law demo
> from Sargent Welch. It consists of two 1-in. ID, 3-ft long tubes --
> one aluminum and one clear plastic, hanging from spring scales. The
> explorer drops two visually identical bobs -- one magnetic and one not
> magnetic. -- down the tubes. Both bobs fall normally in the plastic
> tube, and the non-magnetic bob falls normally in the aluminum tube.
> But the magnetic bob falls very slowly in the aluminum tube, and incr
> eases the tube's weight while it is falling. It's very mysterious and
> provides an excellent vehicle for explaining magnetic induction and
>
> Our problem is that the little bobs have a tendency to disappear. I'm
> sure our visitors don't steal them; they must oxidize into pure gases
> in 24 to 48 hours. I called Sargent Welch to get replacement bobs but
> neither they nor their vendor sell only the bobs.
>
> I am soliciting ideas on how to replace the bobs. They are cylindrical
> roughly 3/4-inch diameter and 2-inches long, are visually identical.
> If necessary, we could use non-cylindrical bobs as long as they are
> visually identical and the correct size.
>
> Paul O. Johnson
> Exhibit Developer
> The Science Place
> Dallas, Texas

brian whatcott <inet@intellisys.net>  Altus OK
                Eureka!