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Re: [Phys-l] Centrifugal redux

I'm trying to remember my Piaget theory from college 40 years ago. Was
it something about cement?

Bob at PC

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of John
Clement
Sent: Thursday, March 19, 2009 4:37 PM
To: 'Forum for Physics Educators'
Subject: Re: [Phys-l] Centrifugal redux

While math may give a term in an equation, the interpretation of the
term
depends on your particular definitions and paradigms.

My argument is very simple. Students have extreme difficulty with
reference
frames so we must initially stick to inertial frames. Having them
identify
the sources of forces by identifying the agents is very productive in
building a coherent model. Once this done, and students have a fairly
stable coherent model, you may move on to accelerated frames.

But I submit that calling the terms which can be interpreted as forces
is
still inadvisable at that point in time. There is no disagreement with
the
calculations, just with the words you use to help students understand
the
physics. One of the recent avenues of research has been cognitive
linguistics which shows that how you frame an idea is extremely
important in
whether people believe it.

The centrifugal field is a consequence of the mathematics, and whether
it
exists as a "real" thing is entirely open to interpretation. It can
just as
well be treated as a mathematical artifact which does not appear in an
inertial frame.

One's definition of "real" depends on where you start from, and your
particular assumptions. So if students follow the most productive road
to
understanding, namely interactions, by that assumption centrifugal
forces
are not "real", because there is no agent. If you are willing to let
them
at the beginning presume agentless forces, then centrifugal force is
"real".
But then students add all kinds of things to free body diagrams like
"force
of inertia".

You make your own choice as to what is "real". Piaget pointed out that
reality is your own construction in your own mind, and does not
correspond
exactly to anyone else's. But I would forewarn anyone who wishes to
teach
about the physics that introducing centrifugal force will most likely
cause
great confusion. It most probably needs to be introduced according to
the
sequence I have outlined. Also students need to be acquainted with the
idea
that physics is about building mental models, and that as you learn
more,
these mental models must change, or even sometimes be discarded in favor
of
a new model. Also some of the old mental models remain in place to be
used
in one situation, while the newer model is used in another, even though
they
do not necessarily agree with each other.

The real facts that I have to support my assertions are in any number of
research papers on how students learn physics. For example, one paper
showed that introduction of interactions before Newton's laws improved
understanding of NTN3. Mathematical arguments generally do not persuade
students, and are often treated as just "it is OK to use the equations".
This comes from the MPEX by Redish. If you see the math terms as "real"
thinks, OK. Obviously the pont of my previous posts was not understood.
I
don't care whether anyone believes in centrifugal force. I care whether
a
particular interpretation helps or hinders students, and there is some
research on this topic.

Ignoring how people think sets education back. Not talking about agents
with physics students sets physics education back. Oh, and Newton was
willing to say that God provided the answer when he couldn't figure it
out.

John M. Clement
Houston, TX


It just cracks me up when people just make up facts and principles
to support their opinions.

It's an old trick.
Simplicio says: My opinion is law. Your opinion doesn't count
because it violates such-and-such principle.
Salvatio says: I am not bound by your opinions, or by your
made-up principles.


As of today, this discussion is two layers deep in bogus principles.

The fact is, the centrifugal field is a term in the equation that
gives
the acceleration in one frame in terms of acceleration in another
frame.
The derivation does not even depend on Newton's laws of motion or
other
physics; it's just mathematics. This is not my opinion; this is a
calculation. If you disagree with the calculation, please tell us
which
step of the calculation is wrong.
http://www.av8n.com/physics/rotating-frame.htm

Bogus principle #1: The centrifugal field does not exist.

Bogus principle #2: The centrifugal field does not exist because all
forces have "agents".


I guess if you are going to tout one bogus principle, you might as
well
support it with another bogus principle. What have you got to lose?


Galileo is considered the father of modern science because he
explicitly
separated science from philosophy and metaphysics. The scientific
laws
are required to explain what happens. They are not required to
explain
the why or the how; in particular they are not required to identify
the
"agent". Newton picked up on this idea and expressed it more
succinctly:
Hypotheses non fingo. Talking about "agents" sets all of science back
nearly 400 years.

For example, should this paper have been rejected
http://antwrp.gsfc.nasa.gov/debate/1996/hub_1929.html
on the grounds that it failed to explain the data in terms of a
mechanism
or an "agent"? I don't think so.

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

It is not surprising that people who have never bothered to learn
about
the centrifugal field might conclude that it does not exist. This is
an example of a well known fallacy called _argument from no
evidence_.
This type of fallacy is discussed at
http://www.av8n.com/physics/no-evidence.htm

_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l


_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l