World’s Roundest Object!

March 25, 2013 by 39 Comments

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


39 Replies to “World’s Roundest Object!”

  1. Look at those eye-bags

  2. Remy says:

    if you cut big k in half, which would be the new kilogram?

  3. Worlds Roundest Object: a sphere
    Me: Hold my belt..

  4. Richard says:

    the world is not even really round. its more like a potatoe xD

  5. MN ZEN says:

    Other side of the world: The world's most blocky object

  6. suka blyat says:

    I know what you mean my fushigi ball feels good too.

  7. 2030: world Thiccest objet

  8. ceroenblanco says:

    Did one of those replicas was sent to Venezuela?? O.o

  9. Glad I finally got around to watching this video

  10. I lament the brute force decision to make the kilogram definition a 'fundamental' one and at the same time retiring the Kilogram Prototype. It's a sham.

  11. A drop of water is perfectly round

  12. Amogh Kudva says:

    Danse macabre in background: noticed it after 3 yrs of watching it for first time

  13. this doesn't change the fact that my mum will take 100gram of free vegetables in a bargain.

  14. Alex Cullin says:

    did they redefine it then?

  15. “Worlds roundest object”
    My body: hold my body fat

  16. Why is your face so close?!?

  17. Neo Xu says:

    Isn't 1kg==1024g?

  18. Now definition is changed

  19. The first minute he was looking ridiculously cute getting all that excited in preparation to hold a metal ball 🤩😍 it's absolutely lovely to see childlike expressions on an adult, makes them so effing genuine and unfiltered!

  20. Kinsley Cow says:

    I don't remember this from the arcana

  21. BKMagyk says:

    The only thing I can think of is the Rick and Morty bit about true level.

  22. In our earth perhaps, so I guess that's what the word "world" is suggesting here. There are more round and smooth objects out there, say, like neutron stars. One of those would be (even relatively speaking) smoother than this polished piece shown here.

  23. 6:08 Sure you can… just look at all the humanity overall and see how we change the definitions all the time… even those that physically can't be changed… :'P

  24. Sean Joseph says:

    Weights and measures, so important the NAZI's went around it and protected it and the allies never bombed it.

  25. I am so grateful to be alive today. My girlfriend saved my life last night. This is a selfie I took in the emergency room after having a severe allergic reaction to almonds. I went into anaphylaxis, meaning my face, my lips, my eyes, my tongue, and my throat all started swelling up rapidly, making it almost impossible for me to breathe. I also had a rash all over my entire body, and I was extremely red. Staying alive had never felt more difficult. At one point, my nasal passage was completely blocked, and it was getting more and more difficult to breathe. They shot me up with Benadryl, steroids, they gave me a breathing tube, and even other stuff that I can’t even remember, and it caused all of the swelling and the rash to go away. Because this was a severe allergic reaction, I need to continue taking steroids and Benadryl for the next week, because it is possible that the allergic reactions could come back at any point over the next week. The steroids and Benadryl make me feel like a zombie, and I really want to take care of my health, so this will be my main focus over the next week. I want to thank my amazing girlfriend, who made the decision to take me to the emergency room the second I started feeling itchy. I was hesitant about going, because I didn’t even want to believe this was actually happening. If it weren’t for my girlfriend driving me to the emergency room only minutes after eating the almonds, there is a good chance that I wouldn’t have made it according to the doctor. This has been without a doubt the hardest few days of my life, but I also look at them as the most important few days of my life. These moments have reminded me about what’s really important in life, and it has made me so grateful to even be here on this earth. I will be prioritizing my health over the next week, and I’ll post updates about how I feel. Thank you all for being patient during these difficult times. This week has been NUTS (too soon for jokes? 😅)

  26. Andrew Via says:

    There is literally no reason for this to be a sphere. It would be so much more accurate if it were a cube.

  27. it was smugglled from wakanda

  28. I want to see her in a bikini.

  29. Icecreamdude says:

    Plot twist: It’s just a polished tin foil ball

  30. On 16 Nov. 2018, the Kilogram definition has been officially changed based on Planck's constant.

  31. And The world wonders why the USA sticks with pounds.

    3 minutes later…


  32. Talk about the ultimate Pi calculation….

  33. Funny my channel is mainly about balls.

  34. Mark T. says:

    Looks like your background is Waverley Cemetery out at east Sydney.

  35. Nodrodsky says:

    Why is it always a Million Dollars ?

  36. Wait till you see my test results

  37. F N says:

    Yeah but no one is talking about how much he hit on the scientst at the beginning😎

  38. I dont know, when i was 10 i made a pretty darn round snowball

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