[Phys-L] Re: Energy is primary and fundamental???

[jsd at AV8N.COM (John Denker)]

Yesterday I mentioned the example of airplanes.  The same ideas
apply to things kids can more easily relate to, such as bikes,
skate boards, swings, and even teeter-totters.

In each of those cases (plus airplanes and all the things Brian B.
mentioned) the description in terms of energy is far simpler than
the description in terms of forces.

a) I know a lot of kids who greatly enjoy zooming their bikes up
    and down whatever slopes they can find.  PE is changed to KE
    and back.  I suppose you could analyze it in terms of forces,
    but why would you want to?
b) Skateparks are popping up across the country like mushrooms
    after a rain.
c) I don't know about you, but when I was little I spent a lot
    of time on the swing-set.  Question:  why does it take you
    several cycles to build up to a large amplitude on the swing?
    It's not a force problem, it's an energy problem.
d) The teeter-totter with unequal masses:  big kid close to the
    pivot, little kid far from the pivot.  Yes, you can analyze
    this in terms of forces and torques, but it is really much
    simpler to view it as a gravitational potential energy balance
    question.

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Todd Pedlar wrote:
> In some ways, as a particle physicist,
> I agree that energy is a fundamental quantity.

OK.

>  However, I fail to see any
> pedagogical advantage in trying to introduce what is really a rather
> abstract
> topic in the opening stages of a course.  I have a hard enough time in a
> traditional ordering convincing some students that gravitational potential
> energy actually exists - I can't imagine beginning with energy topics,
> without
> having grounded them in understanding position, velocity and momentum.

I agree that some notion of position is important, but
this isn't a major stumbling block for most students.

Velocity is important.  In particular, the distinction between
velocity and speed becomes important at some point ... but you
can compute KE just fine *before* understanding this distinction.

We agree that energy comes after position and speed ... but kids
are supposed to learn distance=rate*time concepts in elementary
school.
   http://www.sd83.k12.id.us/cur/CR15477.HTM
If you need to review position and rate that's fine, but if these
are the reason for not treating energy as primary and fundamental
(especially in a college course for potential majors!) then I'm
really confused;  please explain.

Momentum can come later.  Force can come even later still.  I'm not
saying you have to do energy first, but there's no deep reason why
it can't come first.

Perhaps the most understandable reason for not doing energy first is
the lack of textbook support.  That's a fixable problem ... maybe not
easily or rapidly fixable ... but there's no deep reason, no reason
/in principle/ why it couldn't be done.