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# Re: [Phys-L] Inference Lab Design

Here's something interesting, though unrelated, about coins. Fun to do as
a short activity/observation/discussion.

Take a bunch of pennies (the year does not matter) and stand them on edge
on a level table. Then gently tap the
table until they all fall down. Students could do this in groups. Give
them a roll (50) each.. First have them predict
the percentage that will fall heads up. Most will say 50%. Most will be
wrong. Try it and see. The answer should
surprise you, as it did me. The challenge for them is to come up with an
explanation. Virtually nobody gets it,
but that's not the point.

I got this idea from a magazine, and have the reference at school for
anyone interested.

Phys-L@Phys-L.org writes:
Thinking about coins, how about measuring the mass of pennys looking for
whether or not age makes a difference. There was a point when the
composition resulting in a large change that is not generally expected.
Of course you would have to assemble the coin sets which could be a pain.

On Aug 14, 2012, at 1:29 AM, Turner, Jacob wrote:

Yes, the coin experiment and Eleusis are both sounding like they may
wind up in the final plans in some manner.

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. 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)

And with Eleusis, I believe if I include it I would have to be confident
in my TAs capacity for roaming the room and keeping people focused on
analyzing what they are doing and coaching them to effective outcomes,
or providing some form of incentive to make them want to obtain maximum
scores. Or do the longer version (non-express) and have a TA playing
the role of God for each group (so either bringing in extra TAs, or
having each group cooperate to play a single hand together... which now
that I think about it may be a nice way to ensure that there is thought
behind each move, as they will discuss with their group what to play
each time, and be competitive with the other groups by nature to an
extent)

Jacob Turner - (208)885-2730
Director of Physics Laboratory Education
University of Idaho

-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of John Denker
Sent: Monday, August 13, 2012 10:12 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] Inference Lab Design

On 08/13/2012 08:22 PM, Turner, Jacob wrote:
Yes, inference covers both deductive and inductive reasoning.

:-)

My primary aim was to ensure that they get a feel for how to "measure
the unmeasurable"

I agree with the sentiment, but it might be clearer to speak of
measuring things that can't be /directly/ measured.

A lot of things in this world are indirect. Being able to see the
indirect solution is a big part of growing up, for people and even for
animals.

baby
............ (fence)
food

The baby creature will proceed directly toward the food and get hung up
on the fence. The grown-up creature will say "nuts with this" and waltz
around the end of the fence.

I have been trying to gauge to what degree I am willing to break away
from measurement.

Emphasizing measurement seems smart IMHO.

So, how about the Twelve Coins puzzle? It's all about measurement ...
and the optimal solution involves measurements that allow /indirect/
inference of the desired information. There's a lot you can do with
this example. Not all of it needs to be done on Day One; you can keep
spiraling back to it.
http://www.av8n.com/physics/twelve-coins.htm
If this is not suitable, please explain why not.

If you want to do this as a real experiment, not just a
Gedankenexperiment, it takes less than 10 minutes to make an equal-arm
balance out of a wooden yardstick.

I tried googling for directions on how to do this, without much
success.
A gross caricature is here
http://collections.infocollections.org/ukedu/en/d/Jr0035e/20.html
Maybe I should write up directions for a nicer version. Hmmmm.
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Forum for Physics Educators
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_______________________________________________
Forum for Physics Educators
Phys-l@phys-l.org
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Joseph J. Bellina, Jr. Ph.D.
Emeritus Professor of Physics
Co-Director
Northern Indiana Science, Mathematics, and Engineering Collaborative
574-276-8294
inquirybellina@comcast.net

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