Re: [Phys-L] Inference Lab Design

[John Denker <jsd@av8n.com>]

Alas on 08/14/2012 03:38 PM, I wrote:
> As a lesson that does not involve inference so much as scientific
> prediction, consider this:  Get two quartz-regulated clocks (or 
> watches), accurate to the nearest second (or better).  Set clock A
> it as a signal to pay attention to the clocks.  Predict that clock 
> A will read 11:01:00 when clock B reads 11:00:00.  Observe again 
> tomorrow.  Note that one second accuracy is one part in 86400, which 
> is rather more precise than anything they did in high school physics
> lab.

An entire line vanished somehow.  That was supposed to say

  As a lesson that does not involve inference so much as scientific
  prediction, consider this:  Get two quartz-regulated clocks (or 
  watches), accurate to the nearest second (or better).  Set clock A
      one minute ahead of clock B.  Set its alarm and use
  that as a signal to pay attention to the clocks.  Predict that clock 
  A will read 11:01:00 when clock B reads 11:00:00.  Observe again 
  tomorrow.  Note that one second accuracy is one part in 86400, which 
  is rather more precise than anything they did in high school physics
  lab.

One might add:  

a) If you want, use a stopwatch to obtain sub-second precision.

b) The importance of super-accurate timing in modern science and technology
can hardly be overstated.  As a familiar example, GPS satellites carry 
clocks accurate to a nanosecond, short-term and long-term.


On 08/13/2012 10:29 PM, Turner, Jacob wrote:

> > With the coin experiment, I would think it unlikely that all groups
> > would get the 3 move solution, but seeing how they think their way to
> > what they get would be nice.  I have to play with how I word the
> > write-up very carefully to avoid skewing their approach though (if I
> > just clipped the solution out of the page you linked, then most everyone
> > would focus on division/elimination. 

Perhaps it would move the discussion in a good direction if I just 
say that the page in question
  http://www.av8n.com/physics/twelve-coins.htm
was written at such a high level as to make it not directly useful 
in the introductory situation we are discussing.  Sorry.

I have just now taken a stab at rewriting the document in two
parts:  (I) an introductory pedagogical discussion, followed
by (II) a more advanced sophisticated discussion.  The new
Part I is a very drafty initial draft, but it is perhaps better
than nothing. Please take a look.  You may need to hit "refresh"
on your browser.

> > Without that, some may think to
> > number the coins, and weight 1-6 against 7-12, then even against odd,
> > and so forth to obtain a variety of combinations, tracking results for
> > each to observe any pattern)

There are about ten different correct ways of looking at this problem,
which is one of the things I like about it.

In particular, weighing "1-6 against 7-12" is only a gnat's eyelash
away from one of the simplest good ways of doing things.  As stated,
"1-6 against 7-12" is a bipartite division.  From there it is only a
small step to a tripartite division, and then we're off to the races.

This has the potential to be extended into a wonderful metacognition
lesson, illustrating the super-important process of taking a new idea
and mulling it over, looking for connections (and contrasts) with a
wide assortment of previously-known ideas.

It can also be used for a little bit of foreshadowing:  You don't want
to teach about entropy on the first day of class, but you can cover
the 12 coins puzzle at an introductory level, then use it as one of
the many motivations for learning about entropy.

Gotta run now.  More later.