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Re: [Phys-l] workable versus unworkable energy



How you talk about energy and work seems to me to depend on how microscopically you want to analyze the situation. For example, if I have a block that increases in temperature I could choose to look at the fact that the average, translational kinetic energy per molecule has increased. How does that happen? Hasn't work been done on the molecules to increase their kinetic energy (on average)? If a molecule has increased in velocity then it has accelerated and therefore a net force has been applied, at least through some small distance, so the conditions for positive work have been satisfied.

It also seems to me that the great technological advance that lead to the industrial revolution was when we figured how to convert _some_ thermalized (thermal) energy into useful work. Prior to the steam engine we only knew how to transfer kinetic and potential energy into thermal energy, or thermal energy from one object to another. The ability to go from thermal to kinetic is a defining point in human development. (Discovery of Warp-Drive technology may be the next! ;-)

Rick

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Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, IN
rtarara@saintmarys.edu
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Free Physics Software
PC & Mac
www.saintmarys.edu/~rtarara/software.html
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----- Original Message ----- From: "John Clement" <clement@hal-pc.org>
To: "'Forum for Physics Educators'" <phys-l@carnot.physics.buffalo.edu>
Sent: Thursday, January 11, 2007 10:29 AM
Subject: Re: [Phys-l] workable versus unworkable energy


While this is technically true, it is confusing as heck to students. They
need to first see energy as something "like" a substance that can be
transferred from one place to another. So the first model of energy
presented to the students needs to emphasize the substance like nature,
which then makes conservation reasonable. However with experience and more
physics courses a more mature understanding can be developed. Any attempt
to define it initially as a property of a system will most probably block
acquisition of conservation reasoning.

I totally agree that the words expended and consumed are unfortunate because
they can imply the creation of energy rather than its transfer, but they can
be used among experts who understand the context without fear of
misunderstanding. But they should not be used with students and the general
public.

John M. Clement
Houston, TX


Energy, what ever its definition, is not a substance, a system's
kinetic energy can not be "expended," Nor can energy be "consumed".
Energy is a property of a system as is its color. Maybe a string
theorist will disagree.



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