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Re: proper definition of a "point particle"



But I wouldn't dream of using the words "storing energy" or
"degrees of freedom" near the beginning of an introductory physics class.
Arons kept telling us that we talk over out students heads.
Regards,
Jack


On Mon, 7 Oct 2002, John Mallinckrodt wrote:

How would you define a "point particle" and is this idea essential in
introductory physics?

Here's what I would say:

In Newtonian mechanics, a "point particle" is a body that has only
one way of "storing" energy--by moving translationally. To use more
advanced terminology, it has "zero internal degrees of freedom."
Despite the implications of its name, it is not generally necessary
for the particle to occupy zero volume although it is necessary to
insure that it cannot or at least does not rotate. (Note that while
the zero volume feature *is* essential to the concept of an ideal
gas, the more important characteristic of "point particles"--zero
internal degrees of freedom--is not!)

I believe the concept is essential to introductory mechanics even if
it is generally not explicitly addressed.

--
John Mallinckrodt mailto:ajm@csupomona.edu
Cal Poly Pomona http://www.csupomona.edu/~ajm

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.


--
"What did Barrow's lectures contain? Bourbaki writes with some
scorn that in his book in a hundred pages of the text there are about 180
drawings. (Concerning Bourbaki's books it can be said that in a thousand
pages there is not one drawing, and it is not at all clear which is
worse.)"
V. I. Arnol'd in
Huygens & Barrow, Newton & Hooke

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.