As you read Part Four, "Conservation of Energy" (Part Four), it will be important to sort out the semantics Professor Feynman uses. In our modern world, and since Professor
Feynman originally gave these lectures, we have come to think of "conservation" as an ecological and economic issue.
Professor Feynman uses "conservation" to describe a set of processes we might call "management" of
energy, or "exchange" of energy. This lecture illustrates the way energy is used and created in natural and human processes.
Our focus for this study is cast upon the nature of energy. "Energy" is one of the basic
components of physics, yet is something that, even today, we know very little about.
Professor Feynman gives the "general" name for energy, "potential energy." That is, energy poised and ready to be expended exists in
a "potential" state. You may have heard energy defined similarly as "the potential to do work."
To a physicist, therefore, energy is a "given." Since the physical universe is populated with things and people that
move, aspirate, and simply exist, the physicist accepts that "something" is behind all of this activity.
In physical science energy is considered to exist in several forms: gravitational, kinetic, heat, elastic,
electrical, chemical, radiant, nuclear, and mass (Feynman, p. 71). Professor Feynman carefully articulates the technical, physical properties of several of these forms, which is useful.
However, the intriguing aspect
of energy is that it exists across such a wide spectrum of the physical universe, forming a bond which unifies a diverse body of forces. For example, light (radiant energy) unifies with the light bulb (mass energy) to
provide electric light. Further, electrical, radiant, and mass energy properties come together to illuminate a room when we flip a light switch.
Conservation of energy suggests that in any energy transaction, energy
changes form, but is never lost. The presumption is that there is a fixed amount of energy in the universe, illustrated by Professor Feynman's "Dennis the Menace" building block example (p. 70-71). That energy, although
it is changing forms constantly, is never lost, that is, it never changes in volume.
In our light bulb example, a kinetic (and perhaps heat) energy transaction generates electricity (electrical energy) which is sent
through a distribution system (mass energy) to a light bulb (more mass energy). It interacts with the light bulb to create light (radiant energy).
The energy changes forms from kinetic to electrical to radiant (by
interacting with mass), so it changes in form. However, it never changes in volume. Even if the transfer is inefficient, the energy "lost" between the generating plant and the light bulb gets redistributed into some
other point in the universe, perhaps to a grounding pole along the way.
We also know that sometimes the application of energy seems to create other forms of energy. Simply rubbing two objects together, applying
kinetic energy, causes heat (heat energy) through friction (a form of mass energy).
Theoretically, no energy is lost or created through the events described in these examples. The energy merely changes forms
continuously.
Feynman even points out that when negatively and positively charged objects come together and disappear, energy remains (p. 83). Based on the mass or the objects, Einstein's formula (E=mc2) helps
physicists calculate the energy released by the disappearance.
Feynman includes other laws of conservation in his lecture: the law of time independence (experimental results do not depend upon absolute time; an
experiment done at one time has the exact same result as the same experiment done at another time); the law of linear momentum (it makes to difference where an experiment is done, the results are the same); and the law
of angular momentum (an apparatus works the same, no matter which angle it sets at, given adjustments for gravity).
As all physical scientists do, Feynman grapples with the nature of energy, admitting that we
understand little about it. In the end, he observes that we also know relatively little about our own energy supply ("energy" is used here in the same way as we would use "fuel")
"Nature," Feynman argues, seems to
provide a magnificent abundance of energy (we use only 2 parts per billion of the sun's energy), and to provide us with massive potential energy (properly harnessed, there is enough energy in 150 gallons of water per
second to power the entire US for one day, in Feynman's time). It is the physicist's dilemma that we know so little about this amazing force.
