Physics
Rotational Inertia
Quick fact
A figure skater can spin faster by pulling their arms in, because they're reducing their moment of inertia.
Why this is interesting
Have you ever noticed how a spinning bicycle wheel stays upright? It's not magic—it's rotational inertia at work!
Read the full explanation
Understanding Rotational Inertia
Rotational inertia is the resistance an object has to changes in its rotational motion. Imagine holding a spinning playground merry-go-round—your body naturally tries to keep it moving unless you apply a force. The more mass an object has and the farther that mass is from the center, the harder it is to stop or change its spin.
A deeper explanation
Rotational inertia depends on two factors: mass and how that mass is distributed relative to the axis of rotation. Objects with more mass concentrated far from the axis have higher rotational inertia, making them harder to start or stop spinning. This principle explains why a tightrope walker uses a long pole—adding mass away from their center helps them balance better by increasing their rotational inertia.