Whirlda

Whirlda's tilted shield sinks lower and rings faster, until it stops dead.

The Physics

Spin a heavy disk on a flat table. As it loses energy and leans lower, its wobble speeds up, then it stops dead in a finite time. For a small tilt, rolling without slipping, the wobble rate rises as the tilt falls.

Ω ∝ α^(−1/2); one model (Moffatt 2000): α ∝ (t₀ − t)^(1/3), Ω ∝ (t₀ − t)^(−1/6)

• Ω: angular speed of the contact point round the table, the wobble rate (rad/s)
• α: tilt angle between disk face and table (rad)
• t: time (s)
• t₀: finite stop time (s)

Moffatt's 2000 model blamed air drag, but vacuum tests and rolling-friction models disagree on the cause.

Honest caveat: The exponent is still debated. The wobble never reaches infinite speed: real contact physics takes over first.

On the shirt

Front: Whirlda, the pixel-art character, with the title. Back: the wobble law, Moffatt's model, the debate over the cause, and the finite-time stop. Printed on a unisex tee.