World’s Roundest Object!

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The world’s roundest object helps solve the longest running problem in measurement — how to define the kilogram.
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A kilogram isn’t what it used to be. Literally. The original name for it was the ‘grave’, proposed in 1793 but it fell victim to the French Revolution like its creator, Lavoisier. So begins the tale of the most unusual SI unit. The kilogram is the only base unit with a prefix in its name, and the only one still defined by a physical artifact, the international prototype kilogram or IPK.

But the problem with this definition has long been apparent. The IPK doesn’t seem to maintain its mass compared to 40 similar cylinders minted at the same time. The goal is therefore to eliminate the kilogram’s dependence on a physical object. Two main approaches are being considered to achieve this end: the Avogadro Project and the Watt Balance.

The Avogadro project aims to redefine Avogadro’s constant (currently defined by the kilogram — the number of atoms in 12 g of carbon-12) and reverse the relationship so that the kilogram is precisely specified by Avogadro’s constant. This method required creating the most perfect sphere on Earth. It is made out of a single crystal of silicon 28 atoms. By carefully measuring the diameter, the volume can be precisely specified. Since the atom spacing of silicon is well known, the number of atoms in a sphere can be accurately calculated. This allows for a very precise determination of Avogadro’s constant.

Special thanks to Katie Green, Dr. David Farrant, the CSIRO, and the National Measurment Institute for their help. Thanks also to Nessy Hill for filming and reviewing earlier drafts of this video.

There is debate as to whether this is truly the roundest object ever created. The Gravity Probe-B rotors are also spherical with very low tolerances such that they may in fact be rounder.

Music by Kevin McLeod ( Decision, Danse Macabre, Scissors

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34 Responses

  1. Inderdeep Kaur says:

    i havent seen the video yet.BUT HOW CAN SOMETHING BE MORE ROUND!!!!!!!!!!

  2. Dinesh Dahiya says:

    Hey what they use to measure the weight of silicon atom???

  3. SilvahDollah says:

    Is this guys name a spin off of veritasirum in harry potter

  4. Alyssa Austin says:

    Does anyone else think he sounds a little like pewdiepie?

  5. TerraBladeFilms says:

    The fact that he went to a graveyard to record that "grave" segment is too funny

  6. Will Sproul says:

    I clicked on a shiny round ball why am I learning science

  7. Pkboy Arceus says:

    Well kilogram ain’t a kilogram anymore

  8. David Gingerich says:

    One mole (a mole is a number, therefore it is not physical) of hydrogen (presumably the most common element in the universe) weighs 1.008 grams. Thumbs up if you want to switch to kilohydromoles!

  9. Cicero 219 says:

    The pound is not defined as the number of kilograms. As it was there first right?

  10. Aaron_Kingtana28 says:

    the earth is flat!so what if im 12
    i KNOW the earth is flat,so don't compare the earth to the
    silicon ball.due to gravity the earth is flat!

  11. Keziah Cadena says:

    It's so satisfying

  12. John's Crazy World says:

    To bad they are redefining the kilogram soon

  13. Avox Music says:

    I’ve seen this video maybe over 30 times on several different locations. I still get interested and watch.

  14. Eduardo AlCaminó says:

    If you touch it won’t it stop being pure round

  15. Frick off you piece ofshof says:

    I can buy a bouncy ball at the dollar store

  16. DamousX Science says:

    A WHAT balance?

  17. AgeOfLight Plays says:

    Does anyone else think he sounds like pewds?

  18. Anon nonA says:


  19. BubbaQ5 says:

    At 1:22 pause it at 1:23 and you will get a really cringey face

  20. FUKKED UP MEMES says:

    i just broke the record because it turns out my nuts are rounder

  21. zimbardo segula says:

    i'd tap that nurse

  22. Mandalore the flatulent says:

    Not anymore! The kilogram has been redefined no longer tied to a physical object but instead is effectively a series of equations that are ridiculously precise and most importantly doesn't loose mass

  23. Jarjit Ganteng says:

    Lol my balls is the roudest

  24. Mr. Crazy says:

    Am i the only one who finds the first few seconds really really weird?
    "Can i hold it? "
    "Only if you be really really careful, laughs "
    After a few seconds, she says
    "it's slippery, be careful. both laugh "

  25. rubyyr says:

    GRaVe meAns sLow

  26. Bruno Jimmy says:

    fake. if it's a perfect ball it should never keep standing. always in movement.

  27. Isabella says:

    Americans suck.

    -The American

  28. FloppyWaffle - Gaming Tutorials says:

    2:18 just beautiful.

  29. Magical Reverse PRO says:

    The world’s roundest objects are my two balls

    I got from Walmart.

  30. John Goodrich says:

    “As early as 2014” oh boy was that off…

  31. Skippy says:

    Oh look a video where I can find flat earthers being triggered in the comments section

  32. Mansour Alrashedi says:

    this just gave me a headache

  33. Kuni says:

    幹 中文字幕是誰做的 一堆錯字還翻譯的超詭異

  34. Kazuto Kirigaya says:

    What if a line is round and that ball is straight? What defines round?what defines straight?

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