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Spinning Sphere Of Molten Sodium | World's Roundest Object! - At Up-Tube.com

Spinning Sphere of Molten Sodium World's Roundest Object! 9 months ago   08:27

An experiment on how turbulent convection in Earth's core makes a magnetic field
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Huge thanks to Prof. Dan Lathrop and team: http://ve42.co/Lathrop

Companion video to explain Earth's magnetic fields in more detail:

Australians! I'm on my way. I'll be doing live shows in Perth, Sydney and Melbourne. Details and tickets here: http://ve42.co/tour

Find out more about the film Vitamania: http://ve42.co/VITA

Special thanks to Brady Haran and Periodic Videos for sodium vs water footage. Original clip is here:

Special thanks to Patreon supporters:
Donal Botkin, Michael Krugman, Jeff Straathof, Zach Mueller, Ron Neal, Nathan Hansen, Yildiz Kabaran, Terrance Snow, Stan Presolski

I learned a lot in making this video and the one on my second channel with Prof. Jon Arnou. I changed a lot of my preconceptions, specifically I thought:

1. That the Earth's magnetic field was a passive thing - it shouldn't need a continuous input of energy to maintain itself (that seemed reasonable to me because the magnetic field has been around for a long time and it seems mostly stable). But as it turns out, the Earth is a giant electromagnet, and so of course those currents dissipate their energy as they encounter resistance in the liquid metal through which they flow. So the energy to continuously create these currents comes from the kinetic energy of the liquid metal flows in the Earth's outer core.

2. If it's convection, I'm thinking hot things rising, cooler things falling. But apparently the main effect driving convection is the compositional differences at the boundary with the Earth's inner core. This is because of the differential freezing at the boundary. Things like iron freeze into the inner core, while elements like sulfur do not. Hence the pockets of lighter material which then rise outwards.

3. I didn't get why the fluid motion was necessary for the generation of the magnetic field. I mean if it's a conducting liquid, it can conduct currents whether it moves or not. But the key is that the liquid metal can 'trap' magnetic fields. I imagine this like how iron channels magnetic fields. Then once these fields are channeled, they can be pulled and stretched, making more magnetic field.

4. Fluids operate very differently in rotating frames of reference. This is something I didn't intuitively grasp. But, as fluids move from the inner core outwards, those particles are moving much more slowly in the direction of rotation than the matter that has been there for a long time, which means the convection currents get deflected and form helices.

Music by Kevin MacLeod http://incompetech.com Brandenburg Concerto No4

Comments 2426 Comments

junuine yulia
if the magnetic field is gone were doom
I loved that scientist, he seemed super chill and knowledgeable.
I would love to pick his brain for a day
Minecrafter 3929
Yeah not the BS that people say that it’s due to radio activity
I don't like listening to Americans speaking ruined gibberish-'English' - much less listening to them attempt to instruct an audience on the finer points of physics... please make them stop.
So what is the result of this "experiment"?? U r too busy explaining how its works and that safety yadayadayada😅
Gordo Pero Piton
This technology sounds like something that has been around since the 1930s since the aliens brought all of it and we're just trying to soften up the community itsfunneh anything that's spinning really fast with a large amount of mass can definitely produces its own magnetic field
Ruy Vieira
Did the rotating liquid sodium generate a magnetic field or not? So basically the explanation is that Earth has like conductive coils inside it, and because it's moving inside another magnetic field it generates its own?
Vikram Velken
Hypothesis: Global warming is slowing the cooling process of the Earth down, which is the reason for the loss of magnetic field around the Earth.
Bun siua c0a33
There's another interesting theory out there (I think the Geophysics community considers it fringe, if I recall correctly -- but the idea sounds interesting nonetheless): Dr. Hollenbach and Herndon -- "Deep-Earth reactor: Nuclear fission, Helium and the geomagnetic field".
Matthew Rinaldo
This probably won't be read but I think if this experiment was scaled down in size making it easier to rotate the sphere faster, let's say to the actual speed of the earth's rotation. Which off the top of my head is around 1000mph at the equator I believe. Add the tilt of earth and lose the inducted magnetic field, while also adding another layer between the shell and the molten sodium of a substance that will partially insulate the system but not anything that the will react violently or magnetically. That it would yield better result.
Bill A
Just pour some water into the sphere to cool it down... then stand back, faaar back! tsk-tsk
Atria Wulf
what if our magnetic field is produced by trees o3o or at least effected by them
Carlos Vieira
4:47 Dinosaur Comics spotted. I like this guy even more.
Carlos Vieira
Is the curie temperature of iron independent of its phase? I'm pretty sure that iron at those temperatures and pressures isn't Fe-alpha.
Милан Драгић
Earth isn't spining.
jake burn
Is that why people are taller now? Cos gravity is decreasing?
1:06 Sam O’Nella is near.
Laura Tew
Wow! (a) I didn't know you like Trevor Noah (all the best people do!) and (b) I didn't know you were originally from RSA. I can't detect that accent lol. So proud of you Derek!
I don't know why that weird question just jumped in that monkey brain of mine... Could weakening of the earth magnetic field have anything to do with, let's say... climate warming?
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World's Roundest Object! Spinning Sphere of Molten Sodium 9 months ago   11:44

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 (incompetech.com) Decision, Danse Macabre, Scissors

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