🌀 Moment of Inertia — two masses on a spinning rod

Rotational inertia depends on WHERE the mass sits, not just how much. General law: I = Σmᵢrᵢ² = m₁r² + m₂r². The two masses need NOT be equal — bigger spheres = more mass. Push them out (bigger r) and I grows as r²; the same torque then gives less angular acceleration (α = τ/I) so the spin ω builds up more slowly. Spheres are same-density, so radius ∝ ∛mass (10× mass ≈ 2.15× radius).