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Re: [Phys-l] teaching energy



A Modeler would argue that how energy is being expressed is not what energy IS. Energy produces changes of some kind that, given proper conditions, can be observed: A change in speed, in arrangement, etc. Seeing energies as being FUNDAMENTALLY "the same" makes conservation of energy easier to understand FOR A BEGINNING PHYSICS STUDENT. How do you change KE into PE if they are fundamentally different things? What is the mechanism for the "change". What is actually different about them?

The following quotes are attributable to Jack Uretsky, not Bob LaMontagne...

The problem with the dialogue in this listserv is that high school teachers and college professors are dealing with quite different populations, levels of physics experience, IQs, etc. I can't just "write a Lagrangian (see hep-ph/0609015 in the ArXiV)". I can't just "stick to the mathematical descriptions and physical demonstrations and let each student construct his/her own images". I'm not dealing with YOUR STUDENTS, I'm dealing with MY students! I don't consider "that it is dangerously and arrogantly presumptious to try to decide what kind of imagery might be appropriate for a student" - I am REQUIRED to do exactly that to teach my course. Would you prefer that NO physics be taught outside the hallowed halls of the university? If that were the case, then a lot of you would be out of a job since it is the instruction done by high school teachers that leads many of them to pursue YOUR courses!

Bob, you write "I don't think I really became comfortable with energy until I encountered graduate school level mechanics and the concepts of action and the Lagrangian". That's as may be, but my students have a decent grasp of energy models, and understand that energy can transfer to other objects through radiation, working, and heating. They understand that SOME change in the object occurs as a result. They "get" that the energy must balance in an isolated system, and that transfers have to show up as changes in that balance. They can use that understanding to solve problems relating to energy. What more would you expect them to be able to do at THEIR level of experience and knowledge? John Denker was nice enough to give you a very simple illustration of how you would associate PE with a concrete image. I would add a stretched spring (or even rubber band despite Bernard's complaint) as other examples. For stronger students I might drag in bonding and bond lengths. Lots of possibilities. As to your comment "I am not sure when I would even dare to present energy to primary or secondary level students", my response is that you wouldn't be working for very long under those conditions. You HAVE to present energy, and despite all the grousing done on here about how high school teachers are DOING this teaching, the fact remains that our kids are the ones taking YOUR classes, allowing all of you to do what you do as you choose to do it.

----- Original Message ----- From: "Bob LaMontagne" <rlamont@postoffice.providence.edu>
To: "'Forum for Physics Educators'" <phys-l@carnot.physics.buffalo.edu>
Sent: Saturday, September 30, 2006 5:44 PM
Subject: Re: [Phys-l] teaching energy


But aren't they really different "flavors"? Kinetic energy is clearly
visible to a student - there's a motion. Even microscopic random thermal KE
can be envisioned by a student. That mental image may not be entirely
correct because of the dependence of KE on v^2, but it is at least a
concrete image.

Potential energies, on the other hand, are way of easily calculating how a
conservative force will change a KE if an object changes position. That is
difficult, if not impossible, for a student to associate with a concrete
image. Without that image, how do you come up with a meaning for "stored".
In what form is it stored. How does it become concrete as KE? I don't think
I really became comfortable with energy until I encountered graduate school
level mechanics and the concepts of action and the Lagrangian.

I also can't imagine how a student forms a concrete image about Conservation
of energy, because it requires a transformation of energy from an entirely
abstract "flavor" (PE) to a concrete "flavor" (KE).

I am not sure when I would even dare to present energy to primary or
secondary level students. Somebody must think they have this all figured out
because it's part of the standards for each grade level.

Bob at PC

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
bounces@carnot.physics.buffalo.edu] On Behalf Of R. McDermott
Sent: Saturday, September 30, 2006 11:17 AM
To: Forum for Physics Educators
Subject: Re: [Phys-l] teaching energy


Bear in mind that we are (mostly) talking about a presentation to high
school students. While what you say is certainly correct, it conveys very
little information to the beginning student that they can use to help them
internalize their learning. By getting them to associate energy with a
location, it is easier for them to deal with TRANSFERS of energy, and with
the concept of working changing the amount of energy, and helps to
eliminate
the common misconception that energy comes in different flavors; ie, that
KE
is somehow different from PE and has to be "converted" by some unknown and
unspecified process. Beginners (most of them anyway) need a framework
that is concrete before they can proceed to abstract.