Moment of Inertia
Spin different shapes, compare I. Builds on Newton's Three Laws.
Three objects — a solid sphere, a solid cylinder, and a hollow cylinder — all have the same mass and radius. They're released simultaneously from the top of the same ramp.
Which reaches the bottom first?
The solid sphere wins every time! Mass doesn't matter — only how that mass is distributed.
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Watch the three shapes race. The sphere always wins because its mass is closest to the center.
I = cmR²
c is the shape's 'stubbornness' — smaller c means easier to spin, faster to roll
Solid balls roll faster than hollow ones of the same size
Racing cars use light rims to reduce rotational inertia and accelerate faster
Pulling arms in reduces I, making the skater spin faster
“It's not how much mass you have — it's where you put it.”
Inertia Explorer
Build your own shapes and race them. See how mass distribution changes everything.
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Try making a ring vs a disk of the same mass. The disk always wins. Now try adding mass to the center of the ring — does it speed up?
The moment of inertia depends on how far each bit of mass is from the rotation axis. Mass at the center contributes almost nothing to I.