  We present a highly simplified model of the dynamical structure of a disk
galaxy where only two parameters fully determine the solution, mass and angular
momentum. We show through simple physical scalings that once the mass has been
fixed, the angular momentum parameter $\lambda$ is expected to regulate such
critical galactic disk properties as colour, thickness of the disk and disk to
bulge ratio. It is hence expected to be the determinant physical ingredient
resulting in a given Hubble type. A simple analytic estimate of $\lambda$ for
an observed system is provided. An explicit comparison of the distribution of
several galactic parameters against both Hubble type and $\lambda$ is performed
using observed galaxies. Both such distributions exhibit highly similar
characteristics for all galactic properties studied, suggesting $\lambda$ as a
physically motivated classification parameter for disk galaxies.
