[SEL] OT: Physics Help & error correction

Orrin B Iseminger obise at moscow.com
Sun Apr 10 14:54:42 PDT 2011


-----Original Message-----
From: sel-bounces at lists.stationary-engine.com
[mailto:sel-bounces at lists.stationary-engine.com] On Behalf Of Rob Skinner
Sent: Friday, April 08, 2011 6:38 AM
To: The SEL email discussion list
Subject: Re: [SEL] OT: Physics Help

 

On Apr 7, 2011, at 8:49 AM, Orrin B Iseminger wrote:

 

> You can do it, too, Devin.  The most important thing for you to

> remember is to plug not only numbers into your equations; but, words as

> well.  If you do that, problems solve themselves.  For instance:

 

Orrin, are you sure you're not teaching Devin about Chemistry, and not
Physics? The reason I ask is that concept is what I took with me after being
paroled from Miss Holey's high school chemistry class. The lady was so mean,
that rather than kick insubordinate teenagers out of her class, she would
keep us there and cruelly inflict Chemistry upon us. 

 

Upon me, she caused permanent scarring. To this day, I still suffer a
variant of Stockholm Syndrome, where I am obsessive about adding labels to
every item in an equation. While figuring out anything complex enough to
require pencil and paper, I compulsively add labels. If someone comes to me
with a problem that is not properly labeled, I do not even want to talk to
them until they properly construct the equation. 

 

Devin, even if the math is simple, add the labels. Your equations will be
self-checking. If your labels end up all screwy, you know that you goofed it
up. If your labels end up just as you expect, it's an indication that you've
done a good job.

 

~~~~~~~~~~~~~~~~~~~~~~~~~

 

Rob, you blew my cover.  :-)  Actually, I *did* learn the importance of
labels (units) in college freshman chemistry class.  It was this way:

 

Our freshman chemistry class was lucky enough to have Doc Willard teach us.
He was the best and we students were smart enough to know we had a gem for
an instructor. When he sidetracked onto his involvement in the Manhattan
Project he kept all of us sitting on the edge of our seats.

 

Unfortunately, the dolts in charge of our laboratory sessions--more brain
dead graduate student TAs--couldn't explain the difference between a mole
and a graduated cylinder.  They were the ones who were supposed to be
teaching us how to work the problems.  None of us caught on, except for one
fellow, Jim Wilhelm, the class genius.  We were lucky enough to have him in
our little circle of friends.

 

Just like everybody else in the class (except Jim), when it came to test
time, I flunked all the problem-solving questions.  To keep the whole class
from flunking, Doc Willard was forced to grade on the curve.  

 

I was still completely in the dark until the night before the final exam for
the year.  Our little clique got together in the basement of a frat house in
order to cram for finals.  One little question of mine revealed to Jim what
I didn't understand.  In about two sentences he showed me the big picture; I
saw the light.  It is something the graduate students couldn't do in a whole
year's-worth of four-hour labs.  

 

>From then, on, I knew how to deal with those very important labels (units of
measure).  The next day Jim and I aced the final exam and in the process we
blew Doc Willard's grading curve, sky-high.   He posted Jim's and my grades
as A++++

 

End of story.  Now, I need to wipe the egg off my face.  In an earlier post
I said:

 

Actually, it is much better to use fractional notation like this:

 

    32-feet

  -----------

      sec

     -----

      sec

 

And went on to say:

 

In the above example, remember how you divide fractions.  Invert and
multiply.  Therefore, it is entirely correct to do the same in the above.
Inverting and multiplying results in:  

 

32-feet-second

--------------

     sec

 

That is wrong!  I failed to do what I said to do, invert and multiply.

 

   32-feet           32-feet           1          32-feet

--------------  =  -----------  X  ---------  = ------------ 

     sec               sec            sec        sec squared

    -----

     sec

 

Sorry about that, Devin.

 

Orrin

 

Orrin Iseminger

Colton, Washington, USA

http://users.moscow.com/oiseming/lc_ant_p/menu.htm

So many projects.  So little time.   




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