World's Roundest Object!

Veritasium · 38.5M views · 2013-03-25 · 11:44

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Overview

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.

On Hacker News

Recommended in kilogram-redefinition threads as a clear, short explainer of the Avogadro and Planck approaches.

Recommended by 6 HN people across 4 months · HN mentions 2013–2018

Topics

Physics & space (other)Fundamental physics

What people said

gsteinb88 · 2014-07 · Strong recommendation
Fantastic video by Vertiasium on this: [VIDEO] (side note: that video is about a sphere, but the current standard kilogram and its copies are actually shaped like little bells)
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kunai · 2013-10 · Strong recommendation
For anyone interested in the Planck and Avogadro projects to redefine the kilo, this video is an imperative watch: [VIDEO]
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aexaey · 2015-11 · Recommendation
One cubic centimetre of water at 4 degrees Celsius used to define one gram (or more precisely one litre -> one kilogram, which comes out to be the exact same thing) [1], [2]. Although 1 cm^3 of water is still pretty damn close to 1g. [1] [LINK] [2] [VIDEO] (around 1:50, and actually the whole video is excellent)
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Sources

Video by Veritasium, played through YouTube.

HN Library · Source license

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