Re: [Phys-l] g...

[John Denker <jsd@av8n.com>]

On 11/18/2006 06:43 PM, Anthony Lapinski wrote in part:

> Call it whatever you want, but the force of Earth's gravity is the oldest
> known force, 

And that's relevant because ... why, exactly?

ISTM we should present students, especially the beginning students,
with the best available evidence, not the most ancient evidence.

Pedagogy need not recapitulate phylogeny.

> So, to me, gravity is a great place to discuss/introduce acceleration.

I'm not persuaded.

> the least understood of the fundamental forces.

Exactly my point.  That seems like a powerful reason for *not*
using it as the introductory example.

If, as some fine textbooks do, you use the Hookean force in a
certain spring (at a certain extension) as the introductory
example, you can double the force by attaching two springs in
parallel; you can also have opposing forces;  not to mention
innumerable other possibilities.   That's easy to do and easy
to visualize with springs, but not easy -- or intuitive -- with
gravity.

Yeah, I know there are games you can play, such as the multi-Gee
acceleration observed in a trebuchet ... but these are nowhere
near as introductory as hooking two springs to a cart.

>  students that our "true weight" 

IMHO talking about "true weight" is a giant step in the wrong
direction.  If it were truly the true weight, we would just call
it "weight" ... but we don't.  The established notion of weight
corresponds to what some folks are calling apparent weight ...
which means that his "true" weight is not truly "the" weight.
What a nightmare.  Also people are getting sloppy about the
whether the change in weight is due to the motion of the object
(wrong) or the motion of the reference frame (right).

Here's my take on the definition of weight:
  http://www.av8n.com/physics/weight.htm
(That document not responsive to the original question, but it
addresses some side-issues that have come up.)