Re: ENERGY BEFORE Q

[Ludwik Kowalski <kowalskiL@MAIL.MONTCLAIR.EDU>]

I have to read the replies again and think about suggestions.
For the time being let me share one observation.

"Carl E. Mungan" wrote (in part):

> 5. Point out that PE involves an interaction between two objects:
> ball and earth for gravity, or two masses for a diatomic spring. But
> the PE doesn't belong to either. It belongs to the system of two
> objects (plus their field, if you have introduced that concept
> already in class).

1) You are correct. But most textbooks say that an elevated
object "has a potential energy =m*g*h." Can this be
tolerated in the very first encounter with PE? If not then why
not? What is wrong with being tolerant first and elaborating
on the subject later, most likely in the same course?

2) Need for tolerance would disappear if the law of
universal gravitation were introduced before energy.
I see no problem with this (except that the textbook
I am using is not structured in that way).

3) But the issue of being tolerant will always be with us.
It is impossible to say everything known about a topic
when it is first introduced. That what I was thinking
about while reading JohnD's reply. Spiral approaches
are natural; it is impossible to avoid them in teaching.
But spiral approaches in which accepted definitions of
concepts (such as work) are changed in subsequent
considerations are not acceptable, in my opinion.
Ludwik Kowalski