Fig. 1.1. Representation of at vector through different components: ur ~ Qartesian
components; v‘ — contravariant components; vi f covariant components [v, = 1:5,
(MA = (1M)B> (1'”)A # (v‘)B, (MA 94 (v@)B]
The momentum equations are said to be in “strong conservation form” if
all terms have the form of the divergence of a vector or tensor. This is possible for the component form of the equations only when components in fixed
directions are used. A coordinate—oriented vector component turns with the
coordinate direction and an “apparent force” is required to produce the turn-
ing; these-forceserenon-eonservativeirrthe’scr1sellefined1rboveTFor’eJzamplef
in cylindrical coordinates the radial and circumferential directions change so
the components of a spatially constant vector (e.g. a uniform velocity field)
vary with -r and 9 and are singular" at the coordinate origin. To account
for this, the equations in terms of these components contain centrifugal and
Coriolis force terms.