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[Phys-L] Re: Mississippi puzzle



There's also that amount that goes to replenish the aquifer gobbled up
by all those wells. Of course some goes into the river as sewage.

This might explain the 10 X difference Matt calc'd.

Here in CA after the dry Summer, there is no runoff from the first rain.

bc

p.s. Turning day after day is different from making an estimate for a
new question w/ no research.

Brian Whatcott wrote:

Talk of psychological impediments in connection with guesstimates
that turned out to be one to three orders of magnitude out is not
exactly encouraging.

I distinctly recall watching a machinist turn a cylinder of
aluminum alloy to within a thou or two of a desired one inch
diameter, by eye alone.

Perhaps he was lucky? I don't think so - I have done
something of the same kind too.

So it is a surprise to stack that level of estimate -
an error band of about 0.2% against
two well educated estimates that have an error band of
1000% or 1000000% of nominal value.

Because they were all way high, it looks like a systematic error:
ignoring the circular nature of the water cycle, I imagine.
What comes down, must (mostly ) go up again, I'd think.
And estimating the evaporative loss is seemingly a
difficult chore.

How could one sensibly approach that part of the estimate,
I wonder?

Brian W




-----Original Message-----
From: Forum for Physics Educators [mailto:PHYS-L@list1.ucc.nau.edu] On
Behalf Of John Denker
Sent: Friday, April 08, 2005 12:16 PM
To: PHYS-L@LISTS.NAU.EDU
Subject: Mississippi puzzle

1) How much water flows down the Mississippi (at, say, New Orleans)
in a year, approximately? Don't look anything up. Just estimate
whatever raw data you need.

-- Arno Penzias, when he was in charge of all research at Bell
Labs, liked to spring this question on members of the technical
staff. Woe betide the person who blurted out "I have no idea".
Arno would yell back "you must have SOME idea ... don't tell me
you have no idea ... FIGURE IT OUT."

-- Anybody with a US high-school education "should" be able to
answer this _without_ looking anything up. It just requires
strength of character, i.e. not giving up in the face of a
problem that seems hard. It also requires marshalling lots
of facts that may not, at first glance, have seemed relevant.

2) Find a second independent solution to the Mississippi problem.

-- Somehow knowledge of the first solution is a psychological
impediment to finding the second solution.

-- OTOH if you can reach the same conclusion by two different
avenues, it greatly increases the reliability of the result.



Brian Whatcott Altus OK Eureka!

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