Moment of Inertia
A quantitative measure of a body's rotational inertia - its resistance to changes in rotational motion about a given axis.
Governing formula
I = ∑ m_i r_i² = ∫ r² dm
SI unit
kg·m²
In depth
Moment of inertia depends on total mass and how that mass is distributed relative to the axis of rotation. Mass further from the pivot increases I quadratically.
Examples in the real world
A figure skater pulling her arms inward reduces her moment of inertia, causing her spin rate (ω) to increase drastically to conserve angular momentum.