Ferrofluid-- this stuff.

It's a liquid that reacts to magnets, a liquid that reacts to magnets, and then back to being a liquid, and then back to those crazy alien spikes.

Now these spikes are pretty unbelievable on their own, but what happens when we mix ferrofluid with this stuff?

Come with me to the garage, and we'll find out.

And don't try this at home.

OK. Cracking the glass vial inside the glow stick for that chemiluminescence.

Now dim the lights.

[music playing] This is amazing.

There's so much physics happening here to make those spikes and then those incredible patterns.

The first interesting physics happening here is that the spikes point along the direction of the magnetic field lines coming from the magnet.

As I bring the magnet up like this, the field lines go upward out of the magnet, and so do the spikes.

You can see the direction of the magnetic field.

As I turn the magnet like this, the spikes follow the magnetic field lines until the field lines in the ferrofluid are horizontal, and the spikes can't form horizontally.

And as you bring the magnet closer, you can see the strength of the field increasing, indicated by the spikes getting closer together.

But why does the ferrofluid follow the magnet in the first place, and why do those spikes form?

Ferrofluid must have some kind of magnetic metal in it like magnetite, but when you drop a metal in a liquid, it usually sinks to the bottom.

To overcome that here, the particles of magnetite must be very, very small like 10 nanometers.

These nanoparticles of metal make all the difference.

They're small enough that even just their kinetic energy or heat motion can overcome the magnetic attraction that would normally cause them to clump together, and then sink.

But the Van Der Waals force also takes effect at the nano scale, attracting the metal together and pulling it out of the liquid.

To overcome this, the nanoparticles are coded in a surfactant, which is a class of molecule that has a polar end and a non-polar end.

Soap is a surfactant.

It helps keep oil and dirt in water when it doesn't want to go in the water.

One end of the surfactant molecule is attracted to the dirt and oil, and in our case, the metal nanoparticles.

So the surfactant can form a coating.

Then the other ends are fine being suspended in the liquid.

So now when the magnet pulls the metal in the ferrofluid, the liquid carrier goes with it, and it all acts as one big pool of alien goo.

The spikes in the ferrofluid form because of the balance between the gravitational pull keeping the liquid down flat, the surface tension, which wants to minimize the surface area, because it's pulling like the threads in stretchy fabric, and the magnetic field which wants to make the metal align with the field lines.

The result is spikes.

Ferrofluid is so full of surprises.

I was inspired to try this experiment by a photographer, who injected water colors into the ferrofluid, and it turned out something like this.

Was my attempt, but it wasn't quite as good as it is.

I was trying to find the coolest thing to do with ferrofluid.

I tried slime.

Eh.

And dry ice, which is cooled down to negative 109 degrees Fahrenheit.

The only notable behavior with this combination was that the dry ice, which repelled the ferrofluid and typically slid down the ferrofluid mound like a ball rolling down a hill, would stay at the top if it was held in the ferrofluid for long enough.

And if I tried to move it off, it would slide back up like a ball rolling up a hill.

Strange.

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[music playing]