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

[mungan at USNA.EDU (Carl Mungan)]

> 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 agree with Michael's notation and the reason I like F_12 is because
I think of the 2nd subscript as a semi-optional sub-subscript: hence
F_1 = sum over i of F_1_i. (Optional because if there are only two
objects of interest then the net force on 1, F_1, is the force on 1
due to 2, F_1_2. The subscript 2 is then only a reminder, which we
can drop when we get tired of writing it.) -Carl
--
Carl E. Mungan, Asst Prof of Physics  410-293-6680 (O) -3729 (F)
Naval Academy Stop 9c, 572C Holloway Rd, Annapolis MD 21402-5002
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