Rotational Inertia
Spin up a solid disc, a hoop, and a solid sphere — all sharing the same mass and radius — under the same applied torque, and watch them visibly pull apart purely because of how each one's mass is spread out from the axle.
What you can adjust
- Mass (each body)
- 0.5 – 4 kg
- Outer radius (each body)
- 0.05 – 0.3 m
- Applied torque
- 0.02 – 0.5 N·m
- Run duration
- 2 – 12 s
All three bodies share this same mass. Mass alone does not decide how hard something is to spin up — where that mass sits relative to the axle matters just as much, which is exactly what this run demonstrates.
All three bodies share this same outer radius. A bigger radius makes every body harder to spin up, but never changes which one wins — that's decided by how the mass is distributed within the radius, not the radius itself.
The same twisting force is applied to all three axles at once. A bigger torque spins every body up faster, but never changes the ORDER they finish in.
How long the torque is applied for. A longer run gives the slower bodies more time to visibly fall behind the faster ones.