. . . . 1
There are many choices of coordinates and unit vectors, such as cylindrical ( $r, \theta, z$) and spherical ( $r, \theta, \phi$) coordinates, but only in the simple Cartesian coordinates are the directions of the unit vectors permanently fixed.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Jess H. Brewer
2004-02-13