Rising and Sinking in Resonance: Mass Distribution Critically Affects Buoyancy-Driven Spheres via Rotational Dynamics

We present experimental results for spherical particles rising and settling in a still fluid. Imposing well-controlled center of mass offset enables us to vary the rotational dynamics selectively by introducing an intrinsic timescale problem. Results are highly sensitive even small degrees offset, rendering this practically relevant parameter itself. further find that, certain ratio vortex shedding (capturing Froude-type similarity), resonance phenomenon sets in. Even though is effect origin, it also strongly affects translational oscillation frequency amplitude, most importantly, drag coefficient. This observation equally applies both heavy light spheres, albeit with slightly different characteristics which we offer explanation. Our findings highlight need consider parameters when trying understand classify path properties spheres.