  The viscosity of the Quark-Gluon Plasma (QGP) is usually described
holographically by the entropy-normalized dynamic viscosity $\eta/s$. However,
other measures of viscosity, such as the kinematic viscosity $\nu$ and the
Reynolds number $Re$, are often useful, and they too should be investigated
from a holographic point of view. We show that a simple model of this kind puts
an upper bound on $Re$ for nearly central collisions at a given temperature;
this upper bound is in very good agreement with the observational lower bound
(from the RHIC facility). Furthermore, in a holographic approach using only
Einstein gravity, $\eta/s$ does not respond to variations of other physical
parameters, while $\nu$ and $Re$ can do so. In particular, it is known that the
magnetic fields arising in peripheral heavy-ion collisions vary strongly with
the impact parameter $b$, and we find that the holographic model predicts that
$\nu$ and $Re$ can also be expected to vary substantially with the magnetic
field and therefore with $b$.
