Re: i,j,k things.

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

Sorry for the wrong date and time in previous messages. And thanks
to those who alerted me.

Timothy Folkerts wrote:

> ... I don't like the expression "F=2i-3j" that has been used as an
> example throughout this thread.  In fact I hate it.  I would always
> write "F = (2N)i - (3N)j". ...

I conclude that you also write unit symbols, such as N, m, kg, etc.,
after each number and symbol in each intermediate expression for
every problem. When I write F=2i-3j I mean exactly what you say,
implicitly. Just a matter of personal preference.

Ludwik Kowalski



> Am I in the minority???
>
> > Symbols i,j,k, for example when used to describe a force F=2i-3j,
> > become "unit vectors" in that  expression. All by themselves they
> > are only place holders. A coordinate system to represent F (a set of
> > three axes) and a unit (to quantify forces) must be chosen to turn
> > i,j,k into unit vectors. Without this they are only symbols.
>
> Perhaps I am misreading you, but I read your paragraph as saying that i,j,k
> become "unit vectors" in the sense that in this equation they have physical
> units (i.e. newtons).  That is, i by itself is a place holder, but in this
> expression it has come to mean "a vector with magnitude 1N pointing along
> the x axis".  So "i" becomes shorthand for "Ni".
>
> I would reserve i,j,k for abstract, dimensionless vectors of magnitude 1,
> so that i(dot)i = 1 (no physical units).  A dimensionless unit vector is
> multiplied by a "dimensioned" scalar to get a "dimensioned" final vector.
>
> Tim Folkerts