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Re: [Phys-l] rich context luncheon meat



I prefer some of the problems from the University of Maryland

http://www.physics.umd.edu/perg/abp/aha/index.html


-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of John Denker
Sent: Thursday, January 27, 2011 9:52 PM
To: Forum for Physics Educators
Subject: [Phys-l] rich context luncheon meat

On 01/27/2011 12:20 PM, Dr. Richard Tarara wrote:

For problem solving the Heller 'rich context'--I call them 'real world'
problems are a good tool. (These have been, probably are, available
online--U of Minnesota)

Let's take a look at the featured examples:
http://groups.physics.umn.edu/physed/Research/CRP/crexample.html

In the first example:
-- It mentions a secret mission but you don't need to know
anything about the nature of the mission.
-- It mentions submarines but you don't need to know anything
about submarines.
-- It mentions the ocean but you don't need to know anything
about the ocean.
-- In the real world, the second captain would be told the
rendezvous time, latitude, and longitude, and would not
need to infer these from the other guy's velocity profile.
-- Unlike in the real world, no details are overspecified or
underspecified.

This is *not* a real-world problem. This is a completely fake
"textbook" problem with a load of window-dressing. It is the
proverbial pig wearing the proverbial lipstick.

In the third example:
-- The headline mentions energy but the problem has little
if any connection to energy per se. There is no attempt
to calculate the energy.
-- It mentions California but you don't need to know anything
about California.
-- It mentions a "recent" earthquake but you don't need to
know anything about that earthquake.
-- It mentions the telephone company but you don't need to
know anything about telephony.

This does not even remotely resemble a real-world question.

By way of contrast, let me tell you -- approximately -- how
this would play out in the real world.

The boss tells you to find out where the damage is to the
cable. He does not specify the method. Just for fun, you
try the method suggested by the "rich context" homework
problem. The (V,I) readings are 6V, 1A at one end and 6V,
0.33A at the other end. So far things more-or-less agree
with the UMN story.

Now we apply some actual real-world knowledge. We know
that the heaviest wire the company would ever use in such
an application is 19 AWG. Copper is expensive. A thinner
gauge is more likely, but let's be generous and go with
19 AWG. That has a resistance of 8 milliohms per foot per
wire (i.e. per half-pair) at 68 degrees F. Therefore the
hypothesis that there is only one short is dead on arrival.
There are at least two shorts. One short is at most 375
feet from the first end, and another is at most 1125 feet
from the second end.

At this point the boss comes over and gives you a dope-slap
and reminds you that the company owns about as many TDRs as
shovels, and suggests that before anybody starts digging
based on your lame-brained high-school-textbook estimate of
the location, they should stick a TDR on the wire and find
out what is really going on, in a way that does not involve
assumptions about the wire gauge, the number of shorts, the
contact resistance of the shorts, et cetera.

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

Don't get me wrong:

I emphasize that actual real-world problems do exist. Actual
rich-context problems do exist. These are important. Schools
need to do a much better job teaching students how to handle
rich-context problems. This includes dealing with overspecified
and underspecified problems. It includes applying facts that
they know about the real world.

The given examples are called rich-context problems ... but
they are nothing of the sort. They are a load of baloney.
They are an embarrassment.
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