Re: Expressing fractions

From: Don A. Gilmore (eromlignod_at_kc.rr.com)
Date: 01/08/05 

Date: Sat, 08 Jan 2005 21:09:55 GMT

"Lee Sau Dan" <danlee@informatik.uni-freiburg.de> wrote in message
news:87sm5bdboq.fsf@informatik.uni-freiburg.de...
>>>>> "Don" == Don A Gilmore <eromlignod@kc.rr.com> writes:

    Don> Well, it's really complex to figure out. Steel is basically
    Don> about twelve times more resistive than copper, but you must
    Don> take into account the diameters, the contact between the coil
    Don> and the core and the contact between coils.

    Don> My latest theory is that the axis of the copper, while not
    Don> the only path, is a solid, attractive path for a majority of
    Don> the electrons. In addition to increased resistance because
    Don> of the length of the wire, the circular flow could cause eddy
    Don> currents in the core, further heating it. Hell, I don't
    Don> know.

>When copper is in contact with iron, the iron rusts first. When the
>iron rusts out, then the copper rusts. This is called preferential
>rusting (or something like that).

It's called "galvanic corrosion". Steel is higher (more anodic) than copper
in the galvanic series, so an electrochemical cell could cause corrosion of
the steel. But this only occurs appreciably when the metals are exposed to
a conducting liquid electrolyte, like sea water.

>When metals are in contact, the
>most reactive one rust first, leaving the others intact. Indeed, with
>this setting, the rusting of that most reactive metal goes faster than
>when this metal isolated from the others. This has bad impact on
>metal-metal junctions connected by soldering material that is less
>reactive. But the good point is that you can prevent a metal from
>rusting by keeping it in touch with a more reactive metal (e.g. iron
>protected by magnesium). This is called sacrificial rusting (of the
>more reactive metal). Connecting the metal to the cathode of a
>battery also does the trick. (That's how a car's metal shell is
>protected from rusting. If the battery runs out, then the will begin
>to rust. So, keep the battery charged!)
>I don't know what kind of steel you have in your guitar string.
>Stainless steel are naturally protected by a thin and transparent and
>hard layer of rust of chromium, which protects the steel inside from
>further rusting. Not sure if this protective coating has good
>conductivity. (You can't remove the coating by scratching the
>stainless steel surface, as the exposed metal contains chromium, which
>rusts immediately to form a new protective layer.) But it can prevent
>the steel from rusting, hence leaving the copper vulnerable.

Piano strings are made from a very high tensile strength, high-carbon steel
(called "music wire"). They are never stainless steel. The copper windings
are bare copper. They last a very long time (pianos over 100 years old are
commonplace) and experience very little corrosion, though it is sometimes
more pronounced if you live near the ocean.

Now all I have to do is figure out what your comments have to do with the
resistance of the string.

Don
Kansas City

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