Re: Pernicious Ideas (was "Faraday's Final Riddle")

[brian whatcott <inet@INTELLISYS.NET>]

At 01:07 10/4/99 -0400, you wrote:
> I don't like to be a "flamer" but this paper propagates the pernicious
> idea (common in engineering circles) that Faraday induction results from
> the "cutting of magnetic field lines" by a conductor. ....
> Bob Sciamanda


I think Bob needs to open up a little, be less circumspect;
let us know what he REALLY thinks.   :-)

But talking about pernicious ideas, I want to remind you all of the
pernicious physics teaching of what should be a basic concept due
to Archimedes, namely how to determine ( or at least estimate) the
 relative density of an objet trouve'.

 On a newsgroup, I suggested taking the dry weight of such an
object then measuring the weight gain of a beaker with water, when
the object is immersed in it, without touching it.
Call this the 'wet weight'. (Actually the weight of the volume
of water displaced)

Divide the dry weight by the 'wet weight' to get the relative density.
I got several notes opposing. From people I knew to be robust,
academically. It was evident they did not believe that
the beaker gained the weight lost by the immersed object.

I noted the same hesitancy on this list, when aerodynamic lift was the
 thread in question.  Does the ground REALLY feel the weight of the
airplane? Though everyone in the NG thread came round to the appropriate
view in the end, it was not before I suggested they ask for their kids
to be shown an Archimedean demo at school.


brian whatcott <inet@intellisys.net>
Altus OK