Re: i,j,k things.

[Timothy Folkerts <tfolkert@TIGER.FHSU.EDU>]

My problem with this is that 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".

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