= Oscillation frequency with fluid added mass
{title2=$\omega^2=k_{\rm restoring}/(m+m_a)$}
Fluid <added mass> increases inertia but need not alter the same restoring <force>. A submerged spring's constant <buoyancy> shifts equilibrium, whereas a pendulum's <buoyancy> reduces its restoring <torque>. Thus an unbounded-fluid sphere has spring <frequency> factor $\sqrt{\rho/(\rho+\rho_f/2)}$ and downward-pendulum factor $\sqrt{(\rho-\rho_f)/(\rho+\rho_f/2)}$. The latter stable configuration requires $\rho>\rho_f$.
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