  Convection is the predominant mechanism by which energy and angular momentum
are transported in the outer portion of the Sun. The resulting overturning
motions are also the primary energy source for the solar magnetic field. An
accurate solar dynamo model therefore requires a complete description of the
convective motions, but these motions remain poorly understood. Studying
stellar convection numerically remains challenging; it occurs within a
parameter regime that is extreme by computational standards. The fluid
properties of the convection zone are characterized in part by the Prandtl
number $\mathrm{Pr}=\nu/\kappa$, where $\nu$ is the kinematic viscosity and
$\kappa$ is the thermal diffusion; in stars, $\mathrm{Pr}$ is extremely low,
$\mathrm{Pr}\approx 10^{-7}$. The influence of $\mathrm{Pr}$ on the convective
motions at the heart of the dynamo is not well understood since most numerical
studies are limited to using $\mathrm{Pr}\approx1$. We systematically vary
$\mathrm{Pr}$ and the degree of thermal forcing, characterized through a
Rayleigh number, to explore its influence on the convective dynamics. For
sufficiently large thermal driving, the simulations reach a so-called
convective free-fall state where diffusion no longer plays an important role in
the interior dynamics. Simulations with a lower $\mathrm{Pr}$ generate faster
convective flows and broader ranges of scales for equivalent levels of thermal
forcing. Characteristics of the spectral distribution of the velocity remain
largely insensitive to changes in $\mathrm{Pr}$. Importantly, we find that
$\mathrm{Pr}$ plays a key role in determining when the free-fall regime is
reached by controlling the thickness of the thermal boundary layer.
