  We study sound propagation in a uniform superfluid gas of Fermi atoms in the
unitary limit. The existence of normal and superfluid components leads to
appearance of two sound modes in the collisional regime, referred to as first
and second sound. The second sound is of particular interest as it is a clear
signal of a superfluid component. Using Landau's two-fluid hydrodynamic theory,
we calculate hydrodynamic sound velocities and these weights in the density
response function. The latter is used to calculate the response to a sudden
modification of the external potential generating pulse propagation. The
amplitude of a pulse which is proportional to the weight in the response
function, is calculated the basis of the approach of Nozieres and Schmitt-Rink
(NSR) for the BCS-BEC crossover. We show that, in a superfluid Fermi gas at
unitarity, the second sound pulse is excited with an appreciate amplitude by
density perturbations.
