What Is Energy?
W. Beaty     Dec 2000

On Fri, 22 Dec 2000, Don wrote:
> Have you done much "work" on energy misconceptions taught in grammar
> school science?  How should we teach kids about what energy is (ie., a
> property of objects, or a magical "substance") and how it is transfered? 
Hi Don! Grammar school nothing, this is a hot topic in education at the graduate level! Fierce debates have broken out on the PHYS-L forum about just this issue. Should university physics professors see energy as "just a property?" Or is energy "substancelike?"

I have lots of opinions, so brace yourself.


The controversy goes directly to the heart of science. More than that, it goes directly to the heart of existence itself. The problem is that the "substancelike" character of a thing is only a limited mental model, and a model which was created by humans. I'm not talking about energy. I'm talking about everything.

Is water a substance? Or is it actually "just a property" of a collection of H2O molecules? We can take it apart into hydrogen and oxygen. We can take apart the molecules, atoms, continuing all the way down to the subatomic particles, and we'll find no "water" anywhere, because water is indeed just a property of something else.

Or more to the point, what we call "water" is a mental model: it is a convenient and very useful illusion that humans have created in order to be able to deal with the world. "Water" is unreal. What is "real" is a set of exitations in the realm below the level of quarks which makes up spacetime vacuum. In other words, if you can take something apart, then only its pieces are "real", and the original object was just a property of its pieces. So take the world apart all the way down to the deepest level, and all you are left with is weird quantum physics fluffy stuff, where particles and empty space are basically the same thing.

Another way to look at this: line up three bottlecaps on the desk. Is the line "real?" Now move one, and the line has vanished. Form them into a triangle. It the triangle "real?" This is important, since the world is made up of things like the line and the triangle, yet at the bottom of everything, all that is really real is a cloud of bottlecaps. To human beings, the patterns are more real than the primoridal stuff that forms the patterns!

"Energy" is like "water," in that if you deeply believe that energy is really a stuff, you'll get messed up, but if you deeply believe that it is just a property, then you'll also get messed up. The word "just" is the sticking point. Everything you experience in your entire life is just a property. If we want to say that energy is not a substance, then that's the same as saying that the everyday world we experience is not real and we shouldn't be teaching kids about it.

Energy, water, and the rest of reality is really out there, but we can only know it by recognizing patterns and building internal mental models. Our models are real to us, and they are incredibly useful. They are the world we know.

The upshot: the concept of "Energy is a Substance" is a very very useful tool for all students to have in their repetiores. Anyone who argues that energy is just a property is correct... but they are directly interfering with education, and are spreading their wilfull ignorance to students in their misguided quest for "that consistancy which is the hobgoblin of little minds."


On the other hand, once you get to the college level in physics, you learn that this "energy-substance" has some strange characteristics which are unlike those of a conventional substance like water. This is not a problem for students. They just learn that energy, if it is a substance, is an unusual substance. Belief that energy is a substance does not create horrible misconceptions. The small misconceptions it does create are effectively treated in college physics classes. People who don't take college physics can safely go on believing that energy is purely substancelike. At the gradeschool level, we can teach that energy is a strange substance, but "substance" it is. This is analogous to teaching that electrons orbit around atoms like a tiny solar system. It is a useful concept, and it paves the way for more advanced concepts taught in higher grades.

ON THE OTHER HAND... heh heh.
In physics, any property which is a "conserved" property is also a substancelike entity. Mass is "conserved", which means that you can't make mass disappear: you can only remove it from a box by transporting it through the walls of the box. If you push mass down in one place, it instantly pops up again in the neighboring place. You can't get rid of it. It's very stuff-like. It's even more stuff-like than water! You can dissasemble water into subatomic particles. The water is gone. But you can't get rid of the water's mass. I conclude that mass is more real, and more substancelike, than water.

But... energy is like mass! It is a "conserved" quantity too. You can't get rid of energy except by moving it from place to place. If mass is like the "ultimate stuff", if it's like "god's tinkertoys", then the same is true of energy. Know what I'm going to say next? E equals M times c^2. Mass-energy equivalence. It says that mass and energy are basically the same "stuff." Mass-energy is the ultimate "stuff." All other concepts of substance pale in comparison.

But because we think that water is "normal", we get the wrong idea that energy is something strange and abstract. The truth is the total opposite. Water is exceedingly strange and bizarre. What is simple, and what's the most "normal" of all "substances", is Mass-energy.

Which pieces of the above are appropriate for school kids? I dunno. I would have to become a K-6 teacher to be able to judge. But maybe I've pointed out some new "mental tools" that might help you to do the job?

Also see:
Reality vs. Reductionism (energy)


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