Re: [Phys-l] energy is well defined.

["Ken Fox" <physicsfox23@gmail.com>]

I don't know if anyone else has read John's notes on Energy. They are very
interesting to me and quickly are over my head. ( 2 hot potatoes can do more
work as long as we keep the cold one as well, I think.)

I want to teach energy to my high school students and would love a
definition and was excited to be told that it is well defined. Then I read
the part of the notes named "Definition of Energy" and several sentences
jumped out at me:
1."It is more important to *understand* energy than to *define* energy. We
can and will define it, but the definition is not super-simple nor
super-concise. The concept of energy is so fundamental that there is no
point in looking for a concise definition in terms of anything more
fundamental."
2."Energy is somewhat abstract. There is no getting around that. You just
have to get used to it – by accumulating experience, seeing how energy
behaves in various situations. As abstractions go, energy is one of the
easiest to understand, because it is so precise and well-behaved."
3."The most important thing about energy is its role in the law of
conservation of energy,...."

I am still looking for the well defined statement of energy, suitable for my
neophytes, but I feel better that what have done in my classes for 40 years
falls into these 3 statements.

Ken Fox



On Feb 16, 2008 8:53 AM, John Denker <jsd@av8n.com> wrote:

> In the context of
>  http://www.av8n.com/physics/energy-counterexample.htm
>
> On 02/16/2008 06:51 AM, carmelo@pacific.net.sg wrote:
>
> > How about heat or thermal energy generated when sands are continuously
> > falling at constant rate on a moving conveyor belt?
>
> Well, how about it?
>
> > Electromagnetic
> > energy generated by friction to what extent measurable?
>
> What about it?
>
> > Zero-point energy measurable?
>
> Yes, it is measurable.  What's the point?
>
> > Energy is *well* defined as "capacity to perform work" or "ability to
> > perform work"?
>
> No, that's not a good definition, for reasons explained in detail at
>  http://www.av8n.com/physics/thermo-laws.htm#sec-workability
>
> Note that the existence of a bad definition does not disprove
> the existence of a good definition.
>
> > It is, of course, better for the students to learn from something
> > concrete, then to abstract...
>
> Maybe that's why Feynman started with an exceedingly concrete
> example of conservation (Dennis and the blocks) before
> abstracting away the concreteness.
>
> Maybe that's why
>  http://www.av8n.com/physics/thermo-laws.htm#sec-energy
> also starts with a series of more-or-less concrete examples
> before abstracting away the concreteness.
>
> ========================
>
> Bottom line:  This brings us to a grand total of zero valid
> counterexamples.
>
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