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ENERGY WITH Q, STEP 1.



"RAUBER, JOEL" wrote:

The way the Physics 2000 text deals with spring
potential energy and energy topics is in this order:

1) Kinetic Energy
2) Gravitational potential energy
3) Work
4) Potential energy in springs.

So that author hasn't found a simple way to present the topic of
spring potential energy without first presenting the work concept.

OK, suppose we conclude (still tentatively) that the concept
of work is needed in the first physics course. We accept the
above sequence. If so then we are ready to move into a more
complicated world of changing temperatures. How do we
begin? My suggestion is to address calorimetry. In fact, in
my textbook calorimetry would be in Chapter 1 or 2, before
kinematics.

6) Suppose calorimety is over; students know that the model
of "caloric" helps us to rate fuels, to introduce useful
concepts (such as specific heat and latent heat) and to make
reliable predictions about changes of temperature. They
know that attempts to assign mass to caloric failed. But
that also know the idea of the "amount" of caloric is very
useful. In my textbook the unit of caloric would be calorie;
I would not bother students with the mechanical equivalent
of heat at this stage. Following the historical approach seems
to be useful in this case. I would use the word "heat" as a
synonym for caloric. But I would try to make clear that
trying to understand its nature head produced a model
which is much better than caloric.

7) OK, let us enter the next thread ENERGY WITH Q. How
to begin? By observing that even a new tennis ball does not
bounce forever, a pendulum does not swing for ever and
a hockey puck does not slide forever. So what happens to
our sum of three energies? That was the question Joule
asked? We can also refer to observations and speculations
of Count Rumford. Joule found that the amount of caloric
generated is always proportional to the decrease of our
sum of three energy. The coefficient of proportionality is
always the same, one calorie per 4.18 J. Traditional lab
activities for finding the mechanical equivalent of heat
are well known and worth promoting in the first course.

8) What is next? Another fighting about words? I hope
not. How to approach the first law of thermodynamics
with imposing it? Is it OK to say, for the time being,
that from now on it should be KE+PEgrv+PEspr+Q
that remains constant? Be patient Jim. So far the above
statement is an old generalization of experimental facts
established by Joule and others. Q stands for the
appearing amount of caloric, a pseudo-fluid, we can
say.

I wish somebody could take over and defend the
traditional approach to the law of conservation of four
forms of energy in the first physics course. I am tired.
Ludwik Kowalski