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Re: "acceleration due to gravity" (high school)



I can imagine Jim Green might be yelling at his monitor, but I'm not sure
why.

I guess there is some implication here that because this thread started from
the viewpoint of a HS-physics question that it must have a simple
discussion. It does not. In fact, I think these are often the hardest
discussions to deal with. Does the wording "acceleration due to gravity"
cause some conceptual and/or learning problems for HS students? I'm sure it
does. It causes similar problems for college students (who are only a
couple years older).

Indeed, my point in mentioning E=mc^2 and general relativity was aimed
exactly at the high-school curriculum. I think most high school physics
teachers discuss special relativity. At least students coming to college
have seen E=mc^2 and they do not think I'm crazy if I use energy units for
expressing mass. And I have seen both high-school books and freshman
college books that give this a fair amount of attention.

So I am saying that Jim's comment seems a bit like "eating one's cake and
having it too." If it is okay to discuss special relativity, E=mc^2, and
the idea that mass and energy are equivalent (in high school), why isn't it
okay to talk about general relativity (in high school)? Do you want to talk
about relativity in high school or not? Is it really that much more
complicated to talk about gravity/acceleration equivalence than to talk
about mass/energy equivalence?

In fact, I think it is easier to talk about gravity/acceleration than to
talk about mass/energy. Energy is too difficult to compare to practical
experience. But students know what forces feel like. It is not difficult
to explain that supporting a 1-kg mass with your hand (against gravity) and
accelerating that same 1-kg mass sideways with an acceleration of 9.8 m/s^2
will feel the same on your hand, and to some extent students can even do
this, except they don't have calibrated hands to know if the feel is really
identical or just similar.

In our general education science course (non-science majors, typically 19
years old) we talk about F=ma and call m the inertial mass, and we talk
about F=Gmm/r^2 and call m the gravitational mass, and we remark how
interesting it is that inertial mass and gravitational mass seem to be the
same property of matter even though they play a major role in what appears
to be two completely separate ideas (acceleration and gravity). And we
might even remark: Gee I wonder if acceleration and gravity might be similar
concepts. And we might even say: This is one of the ideas treated in
Einstein's theory of relativity.

I'm not saying that our general-education students completely understand all
this. But our bright philosophers and English majors and psychology majors
sometimes get a kick out of thinking about these kinds of things, and I
don't see any reason bright high-school students can't do the same. Like I
said, we're giving it a try with 19-years olds. Can't you give it a try
with 17/18 year olds?

Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817