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. Thank you so much for
watching this video, and if you enjoyed it and
you want to keep learning, subscribe. [MUSIC PLAYING]

AMAZING! Ferrofluid + Glow Sticks
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