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# Re: [Phys-l] Fun/cool unit conversion example?

• From: John Denker <jsd@av8n.com>
• Date: Tue, 19 Jan 2010 04:48:41 -0700

On 01/18/2010 05:21 PM, curtis osterhoudt wrote:

Specific gravities: Pb ~ 11;

... from which you can calculate the bore diameter of
a 12-gauge shotgun.
http://www.unc.edu/~rowlett/units/scales/shotguns.html

This falls into the category of wacky unit conversions,
but is a bona-fide real-world example, not in the same
category as facetious units such as gigaslugs per parsec
cubed or furlongs per fortnight.

It is a relatively advanced example, because it is
nonlinear.

More familiar nonlinear measurement schemes include
logarithmic ones: dB, pH, Richter number, et cetera.

If you want some even more complicated nonlinear
conversions, try pressure <--> pressure altitude
or density <--> density altitude:
http://en.wikipedia.org/wiki/Density_altitude

=======

In the category of fun/cool units, I've always been
amused by the abbreviation for the fermi unit:
1 fermi (fm) = 1 femtometer (fm)

On a related note, a facetious non-real-world
conversion would be to compare agriculture to
high-energy physics by calculating the area of
the proverbial broad side of a barn, measured in
barns. One barn = 100 fm^2.

=============

Here's an addition to the list of useful rules of
thumb: The US "nickel" coin weighs 5 grams, very
precisely, by design. It is also approximately
2 mm thick. This makes it a handy reference.

I made up a mnemonic for this: 5 cents, 5 grams,
and 5 to the centimeter.

====================================

In the category of totally facetious units, we have
things like the anti-millihelen, i.e. a face ugly
enough to sink a battleship.

Some additional metric prefix jokes are collected at:
http://www.spy-hill.com/~myers/notes/Metric.html

See also next message.