Aristotle coined the word, from the
Greek, meaning "at work"
Two millennia later, along came
steam engines.
| Physics
education research suggests that puzzle solving - active brainwork - is
the best route to understanding abstract principles. Links here lead
to many puzzling points. |
|
n the 19th century, science
went to work on the problem of finding how to get the most work out of
steam engines.
A new concept
of "energy" evolved which was very different from Aristotle's idea.
The new "energy" is more
abstract, and the concept is more powerful. It's also more subtle.
The words "work," "heat," and "temeperature"
also acquired new meanings, concepts more subtle and more powerful than
the older meanings |
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|
Today
the words "energy," "work," "heat" and "temperature" are amost always used
exclusively in their prescientific senses. The more abstract, scientific
meanings are rarely recognized. |
|
pre-scientific
colloquial
|
scientific
the broadly useful
power concept
|
| Energy:
Something in food and fuel that keeps us and our engines going. |
Energy:
A very abstract something about which we know only how to calculate its
value and that it's conserved. |
| Free
Energy: Energy we get at no cost. |
Free
Energy: Energy
that, statistically, can be transferred as work. (Free
from incoherence.) |
| Work:
Physical or mental effort or activity directed toward
the accomplishment of something, (American Heritage
Dict.) |
Work:
Energy
transferred by mechanisms other than temperature difference. |
| Heat:
A
fluid-like entity that resides within matter and which raises the temperature
of the matter; A feelling from some sensors
in our skin; elevated temperature. |
Heat:
Energy transferred solely because of temperature difference. |
| Temperature:
A
feelling from some sensors in our skin; elevated temperature. |
Temperature:
A
parameter in a statistical distribution which determines the rate at which
heat flows between regions which are at different temperatures. |
Increasing abstractedness from 1685 to 1925:
One definition of energy is
in terms of work being done on an object. Work energy is the product
of the force exerted on the object times the distance over which the force
acts. However, only the component of the force in the direction of
the motion is used in the calculation, and if the force varies, the integral
must be used:
the line integral of the
dot product of two vectors, Force and incremental distance
In general, science concepts become more
and more abstract as science develops. Nevertheless, this definition
is centuries old. Since then, energy has undergone several refinements.
E = mc2
is Einstein's recognition that, in Einstein's
words, "Energy and mass are merely different expressions of the same thing.
This does not say that mass can be converted to energy. This is a
logical equivalence and not a logical mutual exclusion, although mutual
exclusion is the more common (mis)interpretation.. The equivalence
states that if the value of one increases the value of the other increases;
were it a mutual exclusion, one would indeed be "converted to" the other,
that is, when one increases the other would decrease. Einstein's
energy-mass equivalence is a significant increase in abstractness of the
energy concept.
Quantum mechanics takes energy into
further depths of abstraction. Energy and time, taken together, form
a unified-whole "conjugate pair" of variables. The pair has additional
meaning which takes the concept further from arbitrary human influence:
This is the Uncertainty Principle at work. The Uncertainty Principle
is often thought to suggest the opposite, that it bestows some control
on the real world merely by arbitrary choices we make when we measure things.
It does not.
As science has moved into the 21st century,
the energy concept has become less and less important, being replaced by
ever deeper abstractions. |
| Drop
a line over the edge of the top of a high building and hook the handle
of the briefcase sitting on the sidewalk below so you can pull the briefcase
to the top of the building. While you were raising the briefcase
the force you were putting on it was in the same direction as the motion.
You put energy into the briefcase because you were working against gravity.
You get it back as kinetic (motion) energy if you drop it to the sidewalk.
Splat!
However,
carry the brief case along the horizontal sidewalk and the force you are
putting on the briefcase is perpendicular to the motion. No work
done on the briefcase! You added no energy that you can get back
by dropping it to the sidewalk.
Only
the component of force in the direction of motion adds energy to, "does
work on," the briefcase |
.
|
Nevertheless, the older
concepts are powerful tools
and are very useful to those
who master them.
|
Each one represents
another little piece of the world, and using it enables the user to improve
his or her interactions with that world. The deeper abstractions that science
keeps discovering are the discoveries we make by ever extending our abilities
to recognize those patterns of patterns of patterns of...
As
we thus continually refine our knowledge we are following Estling's
prescription "to find out as much about reality as we possibly can in what
time we have and not waste our precious diminishing time..."
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