>> ALEX: Woah!
Hey guys, I'm here, let's get technical.
Check this out, this blew my mind.
With me, I have some water, a hot plate, a pipette and, of course, a pair of safety glasses.
Shoutout to NoCry send me a pair and sponsoring this episode.
*ding*
When I take some water and pipette it on this hot plate, which is turned off and completely
cool, check out what happens.
Pretty typical.
Now check out what happens when I pipette some water onto this hot plate.
WOAH?
That's so cool!
Well, no actually I guess it's hot.
Not to mention, the other day, I was just standing around, minding my business, holding
a ladle of liquid nitrogen, you know, the usual, when I found out that Vsauce had uploaded
a video.
Huh.
Which way IS down?
Excited, I ran to find my computer and start watching, but, in the process, I spilled my
ladle of liquid nitrogen.
As first, I freaked out, you know, I really like my ladle of liquid nitrogen.
But then I saw something cool: when I spilled the liquid nitrogen, it doesn't just make
a puddle and a big ol' mess like water would.
It balls up, and the balls roll around.
Woooooaaah.
What's going on here?
I'll tell you after the wipe!
That is the Leidenfrost effect.
How does it work?
Well, to get to the answer, let's take a look at what I thought the first time I saw
the Leidenfrost effect.
Wow, that's amazing!
But wait, hold up, this can't happen every time, right?
Like, I've seen water boil.
And I was right.
The hot pad with the Leidenfrost effect was at a balmy 220 degrees celsius, or 428 degrees
fahrenheit.
Let's see what happens if we bring that temperature down a little bit, say, to 200
degrees celsius.
It just boils and evaporates like normal.
This is a huge clue as to how the Leidenfrost effect works.
See, we all know that when water gets hot enough, it turns into steam, and the hotter
a substance is, the quicker the water will evaporate when put on it.
So what if we had a surface that was so hot, that the instant water hit it, it turned into
steam.
THAT is how the Leidenfrost effect works.
The moment the water hits that hot plate, a little bit of it evaporates and turns into
steam.
This creates a sorta cushion for the water, a layer of steam between the water droplet
and the hot plate.
Why?
As we discussed in a previous video, which I strongly recommend you check out, click
the i, heat is just a measure of how fast molecules in a thing are moving.
The way things change temperature is they come into contact with either faster or slower
molecules.
All of the molecules bump into each other, and if the end result is the original substance
having faster molecules, the substance just became hotter, and if the end result is the
original substance having slower molecules, the substance just became colder.
If molecules move fast enough, a substance will undergo a phase change.
Gasses have faster moving molecules than liquids and liquids have faster moving molecules than
solids.
That's the skinny, back to the Leidenfrost effect.
When each drop of water hits the plate and a little bit of it evaporates, it creates
that layer of steam.
Because the molecules in the water vapor move faster than molecules in the water, they end
up hitting the water, bouncing into it, some escaping from the edges, and making it a sorta
smooth crescent-like shape.
This is called film boiling...
Hey, does anyone have a kodak?
No, nope, not that type of film.
... and it's because that layer of water vapor insulates the water droplet so well, it just
levitates around and doesn't boil.
MIND BLOWN.
But, wait a second Alex, just Weight a Second heh heh pun.
Does that water just stay in beadlets and fly around forever?
I mean, it has to go evaporate at some point, right?
Yea, it does.
If you just kinda leave the drop of water there, eventually it will go away, but it
will go away very slowly.
This is because air is great for insulting stuff.
To prove it? *snaps fingers* I am now in a wet suit.
I wear this thing all the time when I go surfing, and a lot of other people who engage in beachy
activities and want to stay warm do too.
SciShow has a great video on wetsuits work, but the important thing to know here is that
wetsuits really are wet, there's a layer of water in them.
Now, water is pretty good at insulation, it has a thermal conductivity of .58 watts per
meter kelvin, but you know what's better at insulation that water?
Air.
That's why, when Destin of Smarter Every Day went diving in the frigid waters of Silfra,
Iceland with his wife, they wore drysuits, and not wetsuits, because air has a lower
thermal conductivity than water, thus making it better at insulation and keeping people
warmer.
I'm gonna take this off now.
THAT is why water droplets on the hot plate take so long to evaporate: air is just that
bad at transferring heat.
Speaking of air and insulation, have you ever looked at a pot of 385 degree celsius molten
lead and thought to yourself, man, I really want to put my hand in there.
Well, now you can, thanks to the Leidenfrost effect!
Disclaimer: Please please please for the love of all that is holy please do not try this
at home.
Because the Mythbusters already tried it!
Yup!
As long as you wet your hand before you put it in, the Leidenfrost effect will kick in
and form a sorta glove of air around your hand, thus not making it completely protected.
>> ADAM SAVAGE: One human hand, in molten metal.
Woah!
That's freaky!
You can feel the water boiling against your fingers.
You can feel that SHCCHKK right there.
>> ALEX: Except, once again, do not try that yourself.
It looks cool but they are professionals.
>> PHILIP DEFRANCO: Don't be stupid, stupid.
>> ALEX: The Leidenfrost effect is named after Johann Gottlob Leidenfrost, and 18th century
German doctor who first wrote about the effect in his paper A Tract About Some Qualities
of Common Water in 1756.
In this English translation I found, the paper starts off with "To the most illustrious
Royal Academy of Scientists of Berlin.
John.
G. Leidenfrost offers his reverence and wishes you health."
So he must, he must really like those guys.
Along with Leidenfrost effect, Mr. Leidenfrost also gave us the concept of the Leidenfrost
point, which is the coolest temperature a surface needs to be for a certain substance
to achieve the Leidenfrost effect.
The Leidenfrost point can be derived from equation, Zuber's equation, but that's
too long and complicated to go into here so let's fast forward.
Basically, all you need to know is that the Leidenfrost point changes depending on which
substance you're talking about.
For water is about 220 degrees celsius, but for liquid nitrogen, the temperature of the
floor is high enough.
That's why, going back to one of our first examples, you can spill liquid nitrogen on
the floor and see Leidenfrost effect.
You know, it's pretty hard to get those droplets to stay in one place, whether they
be water or liquid nitrogen, and that's because the layer of gas in between the droplet
and the floor is, as one study puts it, "virtually frictionless."
But what does that mean?
Well, there are two kinds of friction: static friction and kinetic friction.
Think of it like this: imagine I'm trying to push this copy of Turtles all the Way Down.
Now, is it actually going to move if I just lightly press on it?
No, of course not.
Will it move if I push a bit harder.
Yea!
So, naturally, you've got to question, how much force do you have to put into Turtles
All the Way Down, or TAWD, to actually get it to start moving.
That is static friction.
Kinetic friction is the force acting against TAWD when it's in motion, making it a little
hard for me to continue to push.
Lucky for us, and scientists, water droplets levitating around because of the Leidenfrost
effect have a very low static friction and kinetic friction.
That means you don't need too much to get those water droplets going, you'll see that
even the tiniest nudge makes them go crazy, but also, when they start going, it's not
that easy for a droplet to stop, a matter of fact, it's possible for them to travel
a full meter, if not further.
And when friction is out of the equation, liquids can move in some pretty cool ways.
Undergraduate students Carmen Cheng and Matthew Guy at the University of Bath over in England
got the water to move in pretty cool ways.
They found out that if you put water droplets on a hot, serrated surface, the Leidenfrost
effect propels them in a certain direction.
You can even make them climb uphill, or travel a maze, all thanks to the Leidenfrost effect.
Ok, so this is cool and all, but besides being a neat little thing I can show in a video,
can we actually use this effect for anything?
Well, a couple applications have already been discussed on the interwebs.
You can sprinkle a bit of water on your frying pan to see if it's hot enough for the Leidenfrost
effect to occur, thus making it hot enough to make pancakes, this Reactions video talks
how nuclear power plants need to be cooled with water without the Leidenfrost effect
getting in the way, and this SciShow video touches on its applications in cooling electronics
and inkjet printing, but to me, the most mindblowing application of the Leidenfrost effect is powering
Mars.
So, you know how the Leidenfrost effect propels water on a serrated surface?
Well, research done by Dr. Rodrigo Ledesma-Aguilar and Dr. Gary Wells shows that, if you put
water in this little circular grooved contraption, it will continue to spin around and around.
If you put dry ice in that contraption, it too will spin.
Then, with the help of magnets and copper coils, boom: AC Voltage.
There's not a ton of dry ice on Earth, you know, compared to water and whatnot, but you know what has lots of it?
Mars.
NASA's Mars Reconnaissance Orbiter has found that carbon dioxide is a naturally occurring
element over on the red planet, so it there would be an ample amount of dry ice, which
is just frozen carbon dioxide.
Combine that with the Leidenfrost Effect and we've got power stations and, thus, colonies
on Mars.
So when we do get to that red planet, the Leidenfrost effect will be there every step of the way.
Thanks for watching, DFTBA, and explore on.
If you want to experiment with the Leidenfrost effect at home, here's what you'll need.
A hot plate or pan or something you can heat up to 220 degrees, water, a pipette helps,
and, of course, safety glasses.
That brings us to today's phenomenal sponsor, NoCry.
NoCry makes amazing safety glasses for an amazing price.
These things are anti-fog, anti-scratch, anti-glare, lightweight, and they look great.
That rhymes!
Perfect for experimenting, DIYing, really any scenario where you need eye protection,
or if you just wanna look really cool.
Look like I just did a science.
I have the black and green ones, which are my personal favourite, but they also come
in black and orange and white and pink.
Click the link at the top of the description to check them out and grab a pair, and use
code "Technicality" for 15% your order.
That's Technicality for 15% off.
Massive thank to NoCry for sponsoring this episode and supporting Technicality.
If you like this video, it would help out a lot to press the like button, subscribe,
if you haven't already, and check out this other physics experiment I did which involves
disappearing balls ooooooh.
Or check out this video I was talking about earlier where I do an experiment with heat and marshmallows and microwaves!
Thank you to all my Patreons, especially the ones on screen right now, see y'all next time!
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