Moment of inertia measures an object's resistance to rotational acceleration. It depends on both mass and how that mass is distributed relative to the axis of rotation.
What Is Moment of Inertia?
Moment of inertia (I) = Σ(m × r²). A solid disk: I = ½mr². A thin rod through center: I = ml²/12. The further mass is from the axis, the greater the moment of inertia.
Units
- SI: kg·m²
- Imperial: slug·ft²
- 1 slug·ft² = 1.35582 kg·m²
Practical Examples
A figure skater pulls arms in to reduce moment of inertia and spin faster (conservation of angular momentum). Flywheels store energy by concentrating mass at the rim for maximum moment of inertia.
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Frequently Asked Questions
What does moment of inertia measure?
It measures an object's resistance to rotational acceleration. Higher moment of inertia = harder to start or stop spinning.