  The settling behavior of individual spheres in a quiescent fluid was studied
experimentally. The dynamics of the spheres was analyzed in the parameter space
of particle-to-fluid density ratio ($\Gamma$) and Galileo number
($\mathrm{Ga}$), with $\Gamma \in (1.1, 7.9)$ and $\mathrm{Ga} \in (100, 340)$.
The experimental results showed for the first time that the mean trajectory
angle with the vertical exhibits a complex behavior as $\mathrm{Ga}$ and
$\Gamma$ are varied. Numerically predicted regimes such as Vertical Periodic
and Planar Rotating were validated at high $\Gamma$ values. In particular, for
the denser spheres, a clear transition from planar to non-planar trajectories
was observed, accompanied by the emergence of semi-helical trajectories
corresponding to the Planar Rotating Regime. The spectra of trajectory
oscillations were also quantified as a function of $\mathrm{Ga}$, confirming
the existence of oblique oscillating regimes at both low and high frequencies.
The amplitudes of the perpendicular velocities in these regimes were also
quantified and compared with numerical simulations in the literature. The
terminal velocity and drag of the spheres were found to depend on the
particle-to-fluid density ratio, and correlations between the drag coefficient
and particle Reynolds number ($Re_p$) as a function of Ga were established,
allowing for the estimation of drag and settling velocity using $\mathrm{Ga}$,
a control parameter, rather than the response parameter $Re_p$.
