  We present analysis of the near-infrared spectra of 114 rest-frame
UV-selected star-forming galaxies at z~2. By combining the H-alpha spectra with
photometric measurements from observed 0.3--8 micron, we assess the
relationships between kinematics, dynamical masses, inferred gas fractions, and
stellar masses and ages. The H-alpha line widths give a mean dynamical mass
M_dyn=6.9 +/- 0.6 x 10^10 Msun within a typical radius of ~6 kpc, after
excluding AGN. The average dynamical mass is ~2 times larger than the average
stellar mass, and the two agree to within a factor of several for most objects.
However, ~15% of the sample has M_dyn >> M_star. These objects are best fit by
young stellar populations and tend to have high H-alpha equivalent widths,
suggesting that they are young starbursts with large gas masses. Rest-frame
optical luminosity and velocity dispersion are correlated with 4 sigma
significance. Using the local empirical correlation between star formation rate
per unit area and gas surface density, we estimate the mass of the gas
associated with star formation, and find a mean gas fraction of ~50% and a
strong decrease in gas fraction with increasing stellar mass. The masses of gas
and stars combined are considerably better correlated with the dynamical masses
than are the stellar masses alone, and agree to within a factor of three for
85% of the sample. The combination of kinematic measurements, estimates of gas
masses, and stellar population properties suggest that the factor of ~500 range
in stellar mass across the sample cannot be fully explained by intrinsic
differences in the total masses of the galaxies, which vary by a factor of ~40;
the remaining variation is due to the evolution of the stellar population and
the conversion of gas into stars. [Abridged]
