World's Roundest Object!

  • Published on Mar 25, 2013
  • The world's roundest object helps solve the longest running problem in measurement -- how to define the kilogram.
    Support Veritasium on Patreon:
    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
  • Runtime: 11:44
  • veritasium  science  physics  Perfect  sphere  kilogram  avogadro  avogadro project  redefining the kilogram  kilo  metric system  silicon  silicon sphere  silicon-28  silicon 28  watt balance  bipm  history of the kilogram  grave  units  SI units  definition  gram  mass  quantity  weight  weights  kilograms  csiro  kilogram of the archives  kilogramme  definition of the kilogram  unit  perfect sphere  roundest object  world's roundest object  kilogram definition  

Comments • 32 442

  • FusionPointInc
    FusionPointInc 14 hours ago

    My balls are rounder than that.

  • Night Howl
    Night Howl 18 hours ago

    1:05 you didn't just say that.
    Earth isn't that round.
    Remember those asteroids in movies and cartoons? That's what Earth really looks like. Lots of bumps.

  • Love Life
    Love Life 20 hours ago

    The earth is a level plain. Its definately not a globe.

  • scot E. king
    scot E. king Day ago

    The earth is pretty round? Unsubscribed

  • Pilgrim Dust
    Pilgrim Dust Day ago

    And.... 1 kilogram is 2.1441789E+25 atoms of Si! :D

  • Enchanted Gamer9

    Dude back away from the camera

  • Oh Lol
    Oh Lol Day ago

    So its basically an overpriced rounder and bigger marble?

  • Onsen23
    Onsen23 Day ago

    this is why i love to masterbete than education

  • The Guinea Pig ENVADED

    was it turning?

    • The Guinea Pig ENVADED
      The Guinea Pig ENVADED Day ago

      william hay
      I when he first picked it up I didn’t see it turn except the reflection

    • william hay
      william hay Day ago

      The Guinea Pig ENVADED yes imagine you holding a mirror and your spinning it'll pretty much follow you around

  • tera gammons
    tera gammons 2 days ago

    Ur mom is the worlds roundest object.

  • Drew Wilson
    Drew Wilson 2 days ago

    Never knew there was so much math in shapes

  • Mediocre As Hell
    Mediocre As Hell 2 days ago


  • Óscar Escobar
    Óscar Escobar 2 days ago

    Great video

  • Kat Mack
    Kat Mack 2 days ago

    True level!!

  • CapitanoGUC
    CapitanoGUC 2 days ago

    Would give a nice bowling ball :-)

  • Tomeuhh
    Tomeuhh 2 days ago +1

    Les français représentent🤷🏻‍♂️

  • Gautam Verma
    Gautam Verma 2 days ago

    She is sexy.

  • Avarol Official
    Avarol Official 2 days ago

    he reminds me of jugghead from riverdale

  • Christian Kim
    Christian Kim 3 days ago

    I means it's a sphere...

  • Ken Carter
    Ken Carter 3 days ago

    By 2014? This is 2018!!!

  • PlanetaryBrother Yayy

    its the roundest object in the universe

  • IronNote
    IronNote 3 days ago

    That platinum cylinder has been kilogramming like a boss since 1799.

  • TheGerry236
    TheGerry236 3 days ago

    The world most roundest object in earth
    Accept earth and other planets

  • Phalgun KP
    Phalgun KP 3 days ago

    Unfortunately in 2014 the definition of kilogramme wasn't changed !! But a change has been 'proposed' which might come into effect this year -2018

  • Mac Lakatos
    Mac Lakatos 3 days ago


  • prabal nepal
    prabal nepal 4 days ago

    i think this guy is high 🤔🤔🤔

  • Torpedo Fails
    Torpedo Fails 4 days ago +1

    that sphere be thicc

    ARTEMIS HAYDEN 4 days ago

    Dance macabre. I see what you did there with the graves.

  • ClawedMetal 7064
    ClawedMetal 7064 4 days ago

    My mind is no longer

  • MemeWolf
    MemeWolf 4 days ago

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  • Facundo Hormaechea
    Facundo Hormaechea 4 days ago


  • C. Schoenfeld
    C. Schoenfeld 4 days ago

    Um, doesn't defining the kilogram as n number of silicon 28 atoms pretty much just bring us back to square one, where the number of atoms was calculated by measuring the volume of a 1kg sphere of silicon? Why not just calculate the number of H2O atoms of ultra-pure water and go with that?

  • 3nglish Elusive
    3nglish Elusive 4 days ago

    I would bang that nerdy girl silly.

    MOHAMMAD ABDULLAH 4 days ago


  • Xiere Teefv
    Xiere Teefv 4 days ago

    I bet touching it wasn't that amazing

  • PackRat
    PackRat 4 days ago

    "Can i pick it up"
    "sure AS long as your....."
    *SMASHES it

  • Daphne Riversong
    Daphne Riversong 4 days ago

    Was I the only person internally cringing at his French pronunciations? Not to offend him, or anyone, though

  • Brooke
    Brooke 4 days ago

    wow a sphere so cool.

  • EwokMyWeeWok
    EwokMyWeeWok 4 days ago

    History is fake bro why lie

  • Red TheGamingStarts
    Red TheGamingStarts 4 days ago +1

    how did i get here,all i remember is whaching some drone videos

  • La Red
    La Red 4 days ago

    Soooo the Earth 🌏 must not be too round at all??

    • La Red
      La Red 4 days ago

      Plus that I don't buy this LOL..... What about an atom? Microscopic things? Something has to be more round somewhere LOL

  • Catharina Tjahjono
    Catharina Tjahjono 5 days ago

    It looks like its spining in his handbecause when he turns it the other way it still looks the same from the angle 😂

  • Eric Smith
    Eric Smith 5 days ago

    What is the song at 1:37

  • Moxon
    Moxon 5 days ago

    Roundest? are you flat earth people?

  • Eric K
    Eric K 5 days ago

    I can't believe I just watched that whole 11:43 long video.

  • TF24LIFE [P2P]
    TF24LIFE [P2P] 5 days ago

    1:10-1:15 I don’t get what they are saying, what does mountain and valley got to do with the roundest object, she said “about 14 metres apart” like WHAT? what does that mean, that’s just weird, maybe comparisons

  • Katy Yang
    Katy Yang 5 days ago +1

    I want to roll it.

  • fuzzypanther45
    fuzzypanther45 5 days ago

    fun fact: when someone head is cut off their faces are still making emotions the medulla i think its called (the center of all live and "power" of your brain) is still connected to the part of your brain that makes emotions in the face.

  • Greenball Science
    Greenball Science 5 days ago

    How many digits of pi did you use.

  • Greenball Science
    Greenball Science 5 days ago

    I thought the gram was a base unit.

  • Galacticpulse Gaming

    "How much does that worth?"
    -"It's priceless"
    * disappointments on his face *

  • Cameron Cassar
    Cameron Cassar 6 days ago

    I feel asleep

  • Caleb Lackie
    Caleb Lackie 6 days ago +1

    adidas jabulani is rounder

  • Giannis Dravis
    Giannis Dravis 6 days ago

    How can you perfectly calculate something when there's π involved?

  • Ryan Thomson
    Ryan Thomson 6 days ago

    How to define a kilo gram: 1000g

  • Tom van Loon
    Tom van Loon 6 days ago

    Didn't you make it less round and heavier than a kg by touching it?

  • Browns Fan
    Browns Fan 6 days ago

    Can i pick it up? Yeah just be car- TOUCHDOWN

  • Rhamel Spaulding
    Rhamel Spaulding 6 days ago

    is it me or is he high af

  • Courtney
    Courtney 7 days ago

    Earth is not a she, it is a he, and he has a bulge.. just s yall know lol

  • Exp General
    Exp General 7 days ago

    Did he just saw the earth is pretty round, knowing that we have hills, mountains, and etc

  • horus2369
    horus2369 7 days ago

    I'm interested in what a watt balance is

  • Outdoors With Pat
    Outdoors With Pat 7 days ago

    "You can't have a unit that changes it's value" Mhm Bitcoin?

  • François D
    François D 7 days ago

    At what height the kilogram was weighted. Was it at sea level ?
    Was the kilo weighted against a liter of water or the the water weighted against a kilo, and how they knew that a liter of water weighted a kilo since they had to define the kilo against a liter of water.
    It is like the chicken and the egg.

  • mr kikass45
    mr kikass45 7 days ago

    Response to suck it: I do not care about stupid pounds or kilograms. we went to the moon. Suck it.

  • Jonathan Nickerson
    Jonathan Nickerson 8 days ago

    This is bullsh*t

  • Devin Savage
    Devin Savage 8 days ago

    And i thought it was just going to be like a satisfying video

  • RandomShit
    RandomShit 8 days ago

    true level b1tc

  • Cyberchip 047
    Cyberchip 047 8 days ago

    I really wish he dropped it😊

  • iii 3xki
    iii 3xki 8 days ago

    Stupid asshole, the earth isn't exactly "round"

  • originalbot
    originalbot 8 days ago +2

    you are talking too close to the sphere, modifying its weight. thank you for ruining humanity's future,..

    • François D
      François D 7 days ago

      The volume will be modified, not the mass... humanity's future is safe lol

  • ViruqMC
    ViruqMC 9 days ago

    Looks like a fushigi ball to me

  • The Openminded Skeptic

    Legalized it they haved. :D

  • xXBig_BananaXx
    xXBig_BananaXx 9 days ago

    How rounder does round get, like really?

  • General Incredible
    General Incredible 9 days ago

    My Play Doh ball is rounder

  • Barberman
    Barberman 9 days ago

    Deepest ocean Mariana Trench? or real ocean like pacific ocean?

  • 4nc13nt
    4nc13nt 9 days ago

    The people in the market temper with the kilogramm everyday..

  • seanktb
    seanktb 10 days ago

    I wonder how much that thing weighs

  • David Tower
    David Tower 10 days ago

    Tried watching but just cannot get past how nauseatingly close the camera is to this guy's face. Hmm, five pimples, two blackheads, a scar and sixty five nose hairs.

  • memeymarshall
    memeymarshall 10 days ago

    1:05 I wonder how many people shouted at their screens saying "ThE EaRtH IsN'T rOunD it'S fLaT"

  • zombiepixlez gamer
    zombiepixlez gamer 10 days ago

    "the earth is pretty round isnt it?" dumbo the earth is an oblate sphere it isnt perfectly round aside from tall mountains theres the fact that at the equater the earth stretches to be wider due to the speed in which the earth travels.

  • Joshua Tee
    Joshua Tee 10 days ago

    Its ROUNDerful

  • Clorox Bleach :D
    Clorox Bleach :D 10 days ago

    who else knew that the music playing in the backround is from roblox on flood escape?

  • Halil CANDAN
    Halil CANDAN 10 days ago

    Its very interesting. You cause to love science. Thanks

  • Hadi Sulman
    Hadi Sulman 10 days ago

    After watching him explain grave, I think that I have the right to say


  • yehet ohorat
    yehet ohorat 10 days ago

    It looks like his hand is only thing that rotates, not the sphere. Mindblowing 😂

  • James Darnley
    James Darnley 11 days ago

    "By 2014" it's 2018 and this still isn't done😂😂😂😷

  • Gavin Bolanos
    Gavin Bolanos 11 days ago +1

    Im from 2018

  • Franz Liszt
    Franz Liszt 11 days ago +8

    That "danse macabre" in the background c:

    • Chuck Norris
      Chuck Norris 10 days ago +1

      Franz Liszt aaayyy i love ur music

  • ssj Kyto
    ssj Kyto 11 days ago

    I'm just tempted to touch it now

  • lewis pick
    lewis pick 11 days ago

    he sounds like sheldon off the big bank theory

  • HomesickProductions
    HomesickProductions 11 days ago

    *the roundest? Well, you've not seen her assets yet*

  • memorylife
    memorylife 11 days ago

    The song which came befor he holded it crazyblox is the actual guy who made it for game flood escspe in roblox

  • BRNT!
    BRNT! 11 days ago

    I swear hes stoned look at his eyes

  • Prateek Panwar
    Prateek Panwar 11 days ago

    1kg of filtered sand worth 1m euros. I can be millionaire

  • TimOn Tube
    TimOn Tube 12 days ago

    Dirk from Veristablium is leading a charmed existence

  • Haider Abbas
    Haider Abbas 12 days ago

    Counting atoms and all y don't u use just water at 4 ° as definition of kilogram because it is actually what it is

  • EvanThe Legend
    EvanThe Legend 12 days ago


  • AIbinoPo1arBear
    AIbinoPo1arBear 12 days ago

    Paint it like a pokeball and give it to me

  • Robotoon
    Robotoon 12 days ago

    *drops it*

  • Jonathan Hiner
    Jonathan Hiner 12 days ago

    Cuz it is