Spinning Sphere of Molten Sodium World's Roundest Object! 7 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:

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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

Hate Speaker Sargon Of akkad
Legend has it, Trevor Noa is a comedian.
Ducati Dave
The loss of Earth's magnetosphere. Just great. Add that to the other pending world ending events.
Charles Long
Could’t you use liquid mercury? It’s highly conductive, and doesn’t need heat to make it melt.
Strictly Cast RC
Lol im just imagining a flat earther trying to understand this
molten sodium has the same effect of molten iron? This guy is a professor?
Ultimat3Gam3r 1
So if this were to be better and harnessed we could use it as a artificial gravity system for space journeys?
Corpsie Corpsie
Shifts in the Earth's magnetic field causes measurable changes in climate and we don't know in what phase of the Earth's magnetic field cycle it's in?
joseph bodden
i see no mention of the sun's magnetic field, are we not spinning and cutting lines of force?
The Norm Show
Can you do a video explaining how we know that the center of the earth is iron and nickel?
Rich H
Interesting. However, this is all simply theory. Nobody knows for sure what the center of the earth contains. All of this is supposition based on other theoretical information. But it’s work that goes in a direction to further discovery. Remember, 100 years ago a lot of people thought that world was flat. Cool science, but it’s conjecture — at the end he even says “it’s an open question.”
Adds 2 drops of water
are some of these currents eddy currents ?
piet skiet
Thanks for making me even more paranoid !
liquid mercury in the pipes
Liquid sodium core growing when it's cold but how I mean when anything heat up and molten its surface area grow and vice versa if it is cooled but you are saying in a liquid sodium core grows when IT cold
Rodney Mahair
Use a second coil on the bottom
Alx Singler
So basically Prof. Dan Lathrop just admitted FREE energy exists.
Free energy is the ability to make electrons flow for less energy that they put out.
One tiny jolt of heat or current starts a nearly perpetual dynamo that lasts billions of years.
the physics freak
Veritasium:- 2:38 a physicists super fire extinguisher
People:-shouldn't we have that much liquid nitrogen
Douwe Mossterd
What force is driving that core???
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World's Roundest Object! Spinning Sphere of Molten Sodium 7 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