Hi! I’m Hank and this is SciShow. And this is our 790th video!
That’s a lot of videos. So many, that most people haven’t even seen them all, and we
get a lot of requests for video topics we’ve already made.
Now, a ton of you have been here from the beginning and you guys are usually the first
to point out where people can see the topics they’re interested in--thank you for that.
But we wanted to try something new too.
While some of you have been requesting videos we’ve already made, others of you have been
giving us feedback that you want to watch playlists without credits and intros and pre-rolls
interrupting you every four minutes.
So we’re combining those two needs into this:
An extra video about once a month or so that’s a compilation of older episodes we think you’ll
like. They might be recent requests, or a group of videos answering similar questions
and topics. We might even add commentaries to some. Let us know what you think we should
do.
In the meantime, we’ve been getting a lot of requests for winter-related topics, so
here’s some of our favorite videos we’ve made about how fake snow is made, why we can
see our breath in the cold, and killer ice tubes of death! Just to name a few...Most
of them are hosted by me, but there’s a pretty cool experiment in here hosted by Michael
Aranda. Enjoy!
if you enjoy winter then you probablylike all the stuff that winter makes
possible like skiing sledding makingsnowmen and
building snowfall what to do any ofthese things you need
snow and winter does not always equalsnow what if there's not as much snow at yourlocal
ski hill as there usually is ur what have you hosting the WinterOlympics at
a resort on the Black Sea add what have you also don't have asister
who was born with the freakish magical power to freeze anything shewant then
you have to make the snow the nonmagical way the scientific way
and the signs on snowmaking is morecomplex than you might think
shield well
snow is precipitation composed ice crystal unlike sleet or ice pelletswhich
is liquid rain that freezes on its way down to the ground
snow forms when water vapor skips theliquid stage and content is directly
into ice in clouds where temperatures are belowzero
degrees the ice crystal then grows into a snow crystal or snowflake
as it absorbs and freezes more watervapor so making snow is basically all
about creating heat exchange because he have to be removed from water in orderto transform
it into ice crystals this to happen
the ambient air temperature the snowmakers call this the dry bulb
temperature as to be really cold even at 0 degreesany
manufactured snow is likely to be low quality slush but he will beimportant
is the humidity the amount of watervapor in the air when the ambient
temperature is adjusted to account forhumidity it's known as the wet bulb temperaturethis
is important because water cools by evaporating into water vapor
your body uses the same process to coolitself collets wedding coverage too
humid and the air is too saturated thewater can't evaporate as well
which makes it harder to cool down thoseno makers hey I humidity almost as much
as I hate low temperatures they needboth low air temperature
and low humidity when these conditionsare at their sweet spot most snow
machines or snow guns at your favoriteski area can combine called water
and compressed air to create tiny waterdroplets a smaller those droplets are
the better because lots of little drops expose more on the water tothe
cold than fewer big one cell snow guns used special nozzles to spraya fine
mist that snow gods willing freezes almostimmediately
boost their chances most snow machines also shoot that missedhigh up
into the air or even use elevated snow lenses or
snow gun power these allow the superchilled water droplets to stay in the
air longer so they had ample time tofreeze and become that wonderful white
stuff we need for ski so it's not done the same way naturedoes it
is not as easy as pointing your finger it whatever you want
freeze but the science is almost as funand friendly
I don't care where it comes from or howit's made I just one must know because I
want is my Olaf
you may have noticed that when it'sreally cold out your skin
seems to get sticky 10 shipping toappease a bison suddenly is like it's
glued the that your tongue the cold flagpoleoutside
your school and you'll become a legend but not in a good way probablygonna
get all page love your yearbook just polar bears inpictures
from that fateful day why why did you tongue stick to theflagpole
reason is actually really simple even at the effects are notpleasant
their saliva between your time atflagpole and it freezes on contact a
newly formed ice act as a bond between tongue in flagpolealmost
like super glue and let me figure out away to melt the ice like by pouring hot
water on it the only way to separatethat timing that flag pole is through
the path of least resistance and your tongue it gonna put up lessresistance
in the flagpole brute force method can get messy andpainful
but is it then why is the flagpole on your do not lick list forwinter
but not like wooden telephone poles well you onlyfree is
to certain types of materials specifically the ones that are best atconducting
heat let's start with the fact that the inside of your body evenin winter
is always nice and warm and because your body isdoing
its best to keep your organs in fluid around 37 degrees Celsius
even when part iv: you are exposeddirectly to Frigidaire
this is for example why your eyes don'timmediately turn into eyeball snow cones
in cold weather to work with your tissues in the bloodflowing
through the vessels in your head keep them and other parts of your facefrom
getting below freezing and most the time the same heat generation ishappening
on the surface abuse came including
your tongue as long as your body canheat up your skin is faster that he is
transferred away to some think olderhill stay above freezing
things like metal and ice are goodconductors of heat and after a short
time your body can't keep up in his theflagpole
the metal is able to siphon the heat at a year
done faster than your body can replenishit so you stayin gets below freezing
pretty quickly in the saliva turns to I such and other materials likewood
are good conductors your body can replace the heat fast enough to keepyour tissues
oir so if you wanna lick it called woodentelephone
pole you're probably just end up with borders on your tongue but theirdoctor
a lawyer in the room they probably tell you just did not go aroundlooking
stuff summer or winter
Bross and dangerous and no reason I'mtelling you this is so you don't end up
being labeled most likely lose the difftheir tongue
and your school yearbook
At standard pressure, water freezes at zero degrees Celsius and boils at 100 degrees.
Standard science, right?
I mean, the freezing and boiling points of water are how we define the entire Celsius
temperature scale.
Except that water doesn’t always freeze when it’s supposed to.
When the conditions are just right, you can put a bottle of water in the freezer for hours,
and it won’t turn to ice...
… until you make it.
That’s because liquids are subject to a special, weird state known as supercooling,
when the liquid is below its freezing point, but doesn’t solidify.
Liquids don't just suddenly become solid at a certain temperature. There's a process involved,
and it has to do with how molecules line up.
Whether something is a solid, liquid, or gas at constant pressure mostly depends on its
energy, which comes from heat.
In a gas, molecules are warmer, meaning they’re higher in energy. They bounce around a lot,
colliding with each other and flying every which way.
But in a liquid, molecules don’t have as much energy. They’re still moving around,
but they're slowed down enough that bonds form between them, keeping them close together,
and loosely ordered.
Now, at even lower temperatures, where molecules have the least amount of energy, they form
a solid. They’re still vibrating a bit, but at this point the bonds between them are
so strong that they keep the molecules rigidly in place.
Now, let’s talk about the water in the bottle. To freeze, the water needs two things: It
needs to have low energy - that is, it needs to be cold - and it needs to form the intermolecular
bonds that are going to hold it together as a solid.
For this second part to happen, the water has to first form a nucleus, or central point,
of what will eventually be solid ice. This is called a substance’s nucleation site.
It's where the water molecules first slot together in exactly the right way to form
the structure of the ice crystal. This then allows other water molecules around it to
form bonds, spreading out until they all make one solid piece of ice.
However, nucleation sites don't usually happen by themselves; something needs to cause them.
And, often, impurities in water act as nucleation sites. A tiny deposit of some mineral, for
example, could be enough to nudge the molecules around it so they start to arrange themselves
into a solid.
Or sometimes, a nucleus can form if the water is physically disturbed somehow -- say, shaken
up a little. As the very cold water sloshes around, some of the molecules will slot in
next to each other in just the right way, so the water is able to start the process
of turning into ice.
So if you want to supercool water yourself, you have to keep both of those things -- the
impurities and the movement -- from happening.
All you need is a freezer, a watch, and a bottle of standard drugstore-brand purified
water. Don’t use mineral water, because that stuff is full of things that will act
as nucleation sites.
First, just stick your bottle of water in the freezer. We do want it to be below freezing,
but the longer we keep it in there, the more likely the molecules will find a nucleation
site. So around two and a half hours should do the trick.
During that time, don’t open the freezer! The cooling needs to be gradual, and the change
in temperature when you open the door disturbs the water enough that it might find a nucleation
site. So just leave it alone.
If all goes well, when you take the out bottle out, you’ll have yourself some supercooled,
below-freezing liquid water.
But, if you shake it up...
Supercooled liquids are highly unstable. When they’re below their freezing point, their
molecules REALLY WANT to form a solid. Like, REALLY BAD. The laws of physics are commanding
them, but they just can’t comply.
And that is why, with just a slight provocation, those supercooled molecules will snap into
place. By slamming a bottle of supercooled water
against the table, you create a nucleation site, and you can actually see the ice crystal
form almost instantly.
Which is SUPER COOL! Get it? Supercool?
Absolute Zero is the Holy Grail of temperatures -- the temperature at which atoms in any substance
completely stop moving.
But even though we know exactly how cold it is -- -273.15 degrees Celsius -- reaching
it has eluded us for centuries.
For this frustration we have to thank Sir William Thomson, 1st Baron Kelvin, who in
the mid-1800s tested a new theory that heat is just molecules moving around in a substance.
He conducted experiments that drew heat from a warm substance toward a cooler one and found
that at some point, all the kinetic energy could be drained from the warm substance -- it
couldn’t be cooled any further.
This temperature wasn’t like a melting or boiling point. It was the same for every substance.
So Kelvin created a thermodynamic temperature scale that measured the amount of kinetic
energy within any given material. And we still use the Kelvin scale today.
But ever since Kelvin’s day, scientists have been trying to chill stuff to absolute
zero, and none have succeeded. Because, it turns out, quantum mechanics is involved,
which means...well, it’s complicated.
Physicists now know that absolute zero does not mean a complete absence of motion in a
substance. Instead, 0 degrees Kelvin marks the state of minimal motion of a substance's
particles. That's because of Heisenberg’s uncertainty principle, which says that for
any everloving particle in the universe, it’s impossible to know both its momentum and its
exact position at the same time. So, suppose you chill a lump of lead down to the point
that there is NO MOTION going on within it, even at a subatomic level. If you could do
that, you’d know both the particles’ positions and their momentum--which would be zero--
but measuring this is strictly verboten by the uncertainty principle.
So you can't reach true 0 Kelvin, but you can get pretty darn close--like one billionth
of a degree away. And some weird stuff happens when you get that cold: Below about 30 degrees
Kelvin, some substances can become superconductive, meaning they can carry electrical current
with no resistance, which is super-useful when you’re making particle accelerators
or really powerful electromagnets that power MRI machines. Even though superconductors
have been discovered that operate at much warmer temperatures, the development of the
field was all thanks to work at very cold temperatures measured on the Kelvin scale.
Oh, and you might be wondering, because I was: how cold is the coldest place in the
Universe? Is space this cold? Well no, space seems to be fairly uniformly filled with microwave
radiation left over from the Big Bang. This heats deep space to a balmy 2.73 degrees Kelvin.
The coldest natural place known is the Boomerang Nebula , which has been spitting out gas for
so long that it’s cooled down to only 1 degree Kelvin.
And all of this means that in fact the coldest place in the known universe is in laboratories
right here on earth which is pretty cool!
you been doing it since the world can'ton a cold winter day you take a deep
breath let it go and watch Big foggy bellowscome
out your mouth and float away is like making clouds why did thathappen why
I can you see your breath when it's cold out well it because themoisture
in your breath is experiencing a rapid change in dopoint
to point to the temperature at which water vapor starts to condense
out of the air and form liquid just likethey do on your front lawn
when air is warm like in the summer orinside your body the dew points are high
because heat makes water molecules movearound fast in turn into gas
so warmer air can hold more water that'swhy I can get so muddy in the summer
but call their solos these molecules waydown and they begin to condense
as a result lower temperatures oftenmean less moisture in the air
now our lungs no matter what time of theyear kinda like George
in July warm and muggy when you exhalethe air leaving your body is actually
completely saturated with moisture I means the relative humidity of yourbreath
is a hundred percent and when the water vapor in this warm sultrysaturated air
strikes the cold air as water molecule slowdown in quicklycondense
into liquid it's the same mechanism that causes fogmasses
of warm humid air strike in cold air causing condensation these the thingin
order to condense those molecules need something to stick to so theyactually
attach themselves to tiny particles in your breath
called condensation nuclei or even cloudseeds these provide a solid platform for
water vapor to condense into a drop leadto endure cloud seeds are composed of
all kinds of things cert dust cell particles from your lineseven
bit severe proteins and DNA in back scientists are developing a wayto
analyze our exhaled breath condensate or
EBC as it's called the look for thepresent serve air pollutants are signs
of respiratory illness when you see a brother called a it'sborn from
the same phenomena that form clouds and fog
Right about now, below the frozen surface of the Arctic Ocean,
A column of salty liquid is flash freezing the water around it, creating a tube of ice
That can grow fast enough to be observed in real time.
As it stretches down, maybe as much as several meters, this fragile, frozen dagger will make
contact with the sea floor Where it'll create a fast growing web of ice
that can trap and freeze any aquatic life that's too slow to get out of its way.
This otherworldly sounding formation has been called an "Icicle of Death",
But scientists know it as a brinicle, and it is as cool as heck
Unless, of course, you happen to get caught under one, in which case it's just very cold.
We've known about brinicles since the 1960's, But it wasn't until a few years ago that we
got our first really good look at them, Thanks to a BBC documentary that features
some of the craziest time-lapse video you will ever see.
They're found in both the north and south polar seas, usually as winter approaches and
new ice begins to form. Ocean water doesn't freeze like the water
in your freezer or in a freshwater lake - When sea ice freezes on its surface, only
the water freezes And the salt and other ions in the water are
pushed out, leaving behind brine. As the water continues to freeze, this salty,
highly concentrated brine Accumulates in tiny channels and fractures
within the ice And when the ice cracks open just a bit, it
gives the brine an escape route. Because of its high salinity, this liquid
brine is denser and also colder than the water below it,
And since it's so salty, it freezes at a lower temperature than fresh water.
When this super cold, super saline liquid escapes from the sea ice, it begins to sink
And immediately encounters water that's very near its freezing point but still not as cold
as the brine And this is where all that amazing flash freezing
starts. Our briny concoction immediately freezes any
seawater it contacts as it sinks, A fragile tube of ice quickly forms around
the descending plume and thickens as the brinicle stabilizes.
The process continues even if the formation hits the ocean floor, as the still delicate
structure continues to freeze anything it touches.
And that's where things become a little bit dangerous for slow moving critters like sea
stars and urchins - Scientists have reported finding "Black Pools
of Death" under active brinicles or in places that used to have them
Littered with the skeletons of marine animals that couldn't move fast enough as the ice
enveloped them. The study of brinicles is still in its infancy
- there is still much that scientists hope to learn
But let's be patient - arctic water that's -2º Celsius beneath the layers of sea ice
is not exactly the most hospitable research environment.
Still, it might be worth braving those conditions just to see one of them in action
Though, probably, I'm not gonna go check it out.
so this isn't something that we spend a lot of time thinking about the fact that
ice floats on liquid water is really weird
and a really important and not just because it lets you
ice-t_ make that knife tinkling sound but because most aquatic organisms
depend on it if I didn't float than rivers and lakes would
freeze from the bottom up instead of freezing on their services and
all the living things in them would be exposed to cold from both the ice below
and the frigid air above Muslim gangs
wouldn't be able to survive a singleWinter UHV this fortunately
ice does float so it creates an insulating layer between the cold air in
the water allowing organisms to survive in swim all winter long
okay but so why does ice do that first we know why anything floats or sinks
and the answer to that is simply density if the material is more dense than the
fluid that surrounds it it'll sink if it's less dense it'll float
so in short the answer is that ice floats because frozen water is less dense
than liquid water but how is that possible isn't it all just water
and arts solids like definitional a more dense than liquid
not that the nationally usually yes but water molecules are special in the way
that they're shaped and how their electrons are distributed around as we
all know that water is composed of two hydrogen atoms an oxygen atom
but you might not know that oxygen attract electrons more strongly than
hydrogen does result is that the electrons in a water molecule
hang out closer to the oxygen then hydrogens and this gives the oversight
in the molecule a slightly negative charge while the h2 side has a slightly
positive charge this makes water a polar molecule a lot tawaters
coolest and most useful properties
come from this polarity waters in his liquid phase its molecules like in all
liquids I randomly organized but as the water cools the molecules get closer
together and at a certain point starting around four degrees Celsius
they get close enough together that the positive and negative a reserve those
mark you'll start attracting each other and they snap into rigid structure because
water molecules are bent at an angle when they line up like this
the structure they form leaves little holes between them
which makes the structure less dense those tiny holes are the entire reason
that solid water floats on top of its liquid form
so remember that next time you skate on a frozen pond or enjoy a nice
bevy
So I’m going to go enjoy an nice, cozy beverage of your choice. Thanks for watching our first
SciShow Compilation Show. Let us know what you think and what you’d like to see more
of in the comments!