Topic: Energy degradation and dissipation
Articles: “Conserving Energy in Physics and Society” and “Matter
Scatter…”
After reading the article, “Conserving Energy…,” my first
thoughts were “Do we really want to go there?” and “How in the world do we organize
this learning experience?” Let me back
up a moment and fill in a few more details about my experiences with energy
instruction coming into this summer. My
Group A post summarizes how I came to energy pies as the focal point of my
energy instruction. The Modeling materials
I work from separate the energy unit into closed and open systems. First we start with the closed system, where
everything that is part of an interaction is included in the system. Therefore, the conservation of energy holds
true. After about two weeks of that, we
then shift to open systems. Now, an
agent that does work or has work done to it can be outside of the system. Energy is not conserved in this case. Instead, we say that the work done adds to or
subtracts from the total energy of the system.
Simply put, in closed systems we don’t talk about work, in open we do.
I thought this was brilliant on paper. It made perfect sense. The energy pies were a quick, clean, and
simple way to diagram situations. However,
after five semesters following this format, I don’t like parts of it. Specifically, open systems. I think that idea confuses students to no
end. In fact, I've slowly been phasing
that idea out to focus on closed systems for describing every situation. This is certainly what is being suggested in
this article.
On one hand, I really like the Energy Tracking Diagram (ETD)
depicted here. It really does a great
job of summarizing all of the nuts and bolts.
On the other hand, do ETDs ask for too
many details? Do we really need to
follow thermal energy as it spreads to the hand, environment, and spring? Is it important to have students follow
thermal energy everywhere it could possibly go (such as spreading to more and
more objects or spreading spatially)? Or
is that losing precious time with “meaningless arguments” about how much thermal
is here and how much is there, when there might be a final computation that is
a primary outcome, or there might be five other examples I want to look at?
These are all rhetorical questions, of course. I've found myself wrapped in conversation
with my colleagues for long stretches of time on very similar issues; for
instance, a clay ball that is released and “splats” on the ground. Where does more thermal energy end up, in the
ground or in the deformed clay ball? One
of my colleagues and I still don’t agree.
But is that a question I want my students to tackle, or am I simply
interested in having them draw an energy pie scenario that goes from
gravitational à
kinetic à
thermal as the ball is released, arrives just above the floor, and hits the
floor, respectively?
Finally, my second initial question was “How do we organize
this learning experience?” Rather than
taking more time here to answer that, I’d like to see what is done this
summer. I’m quite intrigued by Ross’ “Matter
Scatter” article and the notion of starting first thing with the 2nd
Law and with a concept like “available energy” or “free energy.” I’m curious if the directors have found a
good sequence. I’m also interested in experimenting
with possible sequences myself. It may
be one of my research interests this summer.
