世界上最圆的物体

Veritasium explains the effort to redefine the kilogram, which was still defined by a physical artifact, and how a near-perfect silicon sphere from the Avogadro project helps. It also covers the history of the unit's odd naming.

Why HN likes it: Recommended in kilogram-redefinition threads as a clear, short explainer of the Avogadro and Planck approaches.

“this video is an imperative watch”