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[Phys-l] Fixed paradigms (WAS: buoyancy on a submerged pole)



No you are not missing anything. A simple free body diagram says it all.
When something is firmly on the bottom with no water under it, there is a
large pressure force on the top, and a counterbalancing normal force exerted
by the aquarium bottom by NTN2 (no acceleration). So by NTN3 there the
object is pushing down on the aquarium bottom equal to the force of the
aquarium pushing up. At that point you can put glue or other inelastic
materials between the object and the aquarium as long as you don't allow
water to seep in. The interesting cases where wrangling is fun is when you
have elastic or porous glue.

This sort of wrangling reminds me that students do the same thing. They
have a fixed notion, which they will not give up in the face of overwhelming
evidence. This goes back to a simple experiment in TPT. An instructor had
students in different classes explore NTN3 in different ways. Some classes
were given force probes and asked to figure out how much push each object
exerted on another. Eventually they concluded that the forces were equal.
Other classes were told NTN3 and asked to disprove it using the force
probes. Subsequent testing showed that the "discovery" class had better
understanding and more students "believed" NTN3.

So I am not mystified, but a bit amused that the same type of thing goes on
in professional circles. Fixed paradigms are extremely difficult to
overcome. Even when you know you have such a paradigm it is difficult to
change it. This sort of wrangling is exactly what one sees about the
effectiveness of PER. The "nonbelievers" have a fixed paradigm which stands
in the way of understanding. The psychologists have shown that when you
have a "belief" (fixed paradigm) and it is challenged that you tend to
martial evidence in favor of it and ignore exceptions. This is what the
medieval natural scientists did. They added qualifications to
qualifications in order to preserve an idea rather than radically change it.
So add a deferent, epicycles, epicycles within epicycles... The tea party
global warming deniers are doing the same thing. What you are seeing is a
common social/psychological problem.

And notice one other thing happens. People read something or hear it, and
then later change what they "saw" to fit their fixed paradigms. We all do
this! It is human nature. Haven't you sat down with a student and tried to
explain something only to find out an hour later they still believe the same
naïve things? Of course you have. That was rhetorical question. It works
much better if you can question them and get them to make the correct
conclusions. But on this list Socratic Dialog is nearly impossible. People
just shout at each other and sometimes call each other fools. They often
refuse to read recommended literature that might inform them. But I have
seen a few who have made progress on their own, so eventually this current
thread may be resolved, and it too will pass away, THANKFULLY.

John M. Clement
Houston, TX

I continue to be utterly mystified by all the wrangling about this
"problem" and the many attempts to resolve it experimentally. I
understand very well that "physics is an experimental science" and all
that, but it would appear that some of us think Newton's laws might
actually not apply to this exceedingly simple macroscopic system.

Can somebody explain to me what I'm missing?