[Phys-L] Re: notation for initial velocity components

[edmiston at BLUFFTON.EDU (Edmiston, Mike)]

I'll respond to Carl first, then I have a further complaint and/or
question about subscripts.

It seems to me students ought to understand parentheses fairly well from
their math training and from the typical algebraic calculator; i.e. do
what's in the parentheses first.  Thus (x-dot)sub-0 seems a good choice
to me.  Note this is also the notation Bob Sciamanda recommended.

Also, I have found that double subscripts are a perpetual problem.
Below I will use parentheses to contain the subscripted items.

Suppose we have two objects m(1) and m(2) in contact with each other,
and we are looking at the Newton's 3rd law contact forces.  We might
label these as F(12) and F(21).  Which is which?  Is F(12) the force
exerted on m(1) by m(2), or is F(12) the force m(1) exerts on m(2).
Another example would be two charges exerting Coulomb's Law forces on
each other.

The way I see it, was taught, prefer, is that the subscript nearest the
primary symbol should describe the primary object the force pertains to.
Therefore, the notation F(12) should describe the force experienced by
m(1).  In my way of thinking, F(12) is the force on m(1) because of or
caused by or exerted by m(2).

I checked with my copies of Haliday and Resnick, Arfken et.al.,
Fishbane, and a few other older texts on my shelf, and they all do it
"my way."  However, the textbook I am currently using (Tipler and Mosca)
does it the "backwards way."  Also Serway (another highly used book)
does it "backwards" like Tipler does.

Was there a shift in the thinking on this at some point?  I find this
pretty difficult because it's hard to teach an old dog new tricks,
particularly when the old dog thinks the old tricks are still the right
ones.


Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu