We FINALLY Proved Why Ice Is Slippery

Summary

This video delves into the perplexing slipperiness of ice, a property that has puzzled scientists for centuries. It explores various theories, from the presence of a thin liquid layer to the pressure-induced melting of ice underfoot. Recent research using atomic force microscopy reveals a quasi-liquid layer on the ice's surface, where loosely bound molecules move with a freedom unusual for solids but not quite liquid. The video uncovers the complex interplay of molecular structure, temperature, and friction that makes ice uniquely slippery, challenging our understanding of this common material.

Takeaways

• 🧊 Ice exhibits an unusual property where two blocks can fuse together momentarily, raising questions about its solid-state behavior.
• 🤔 The slipperiness of ice has been a topic of debate for over 160 years, with its surface behavior being particularly perplexing.
• 🔬 Recent research using an atomic force microscope (AFM) has provided the first detailed images of ice's surface at the atomic level.
• 🌡️ The temperature and pressure conditions can significantly affect the slipperiness of ice, with different winter sports favoring specific temperatures.
• 📉 James Thompson's work on the phase diagram of water showed how temperature and pressure affect the state of ice, contradicting the simple liquid layer theory.
• 🛷 The theory that pressure from ice skates melts the ice to create a slippery layer was debunked by experiments showing that the pressure is not sufficient to melt ice.
• 🔥 The idea that friction-generated heat melts the ice surface was considered but is not the primary cause of ice's slipperiness.
• 🔍 Researchers discovered a quasi-liquid layer at the surface of ice, where water molecules are loosely bound and can move more freely than in the solid state.
• ❄️ The surface of ice is composed of hexagonal and cubic ice types, with the boundary between them creating a disordered region that contributes to slipperiness.
• 🌍 This unique behavior of ice being slippery as a solid but less so when a liquid layer forms is a fascinating characteristic of one of Earth's most abundant materials.

Q & A

Why do two blocks of ice fuse together when held in contact for a short time?

When two blocks of ice are held together, the water molecules at the surface of the ice can interact and form hydrogen bonds, leading to the fusion of the two blocks into a single object due to the unique properties of ice.

What is the unusual property of ice's surface that contributes to its slipperiness?

The unusual property of ice's surface is the presence of a quasi-liquid layer. This layer is composed of loosely bound water molecules that are not as rigid as the solid ice beneath them, allowing for movement that contributes to the slipperiness of ice.

Why was it historically thought that ice was slippery due to a thin layer of liquid water on its surface?

In the late 1850s, Michael Faraday conducted experiments that led him to conclude that the slipperiness of ice was due to a thin layer of liquid water on its surface. This theory was supported by the observation that water creates a slippery barrier when spilled on a floor.

What problem arises with the theory that ice is slippery because of a thin layer of liquid water?

The problem with this theory is that ice remains slippery even under extreme vacuum conditions where no liquid layer can be present, as liquid water molecules would have evaporated away due to the lack of atmospheric pressure.

What is the role of atmospheric pressure in the melting of ice?

Atmospheric pressure can affect the melting point of ice. As pressure increases, the melting point of ice decreases, which is why ice can melt under the pressure exerted by an ice skate blade, creating a slippery layer of water.

Why is the idea that pressure alone causes ice to melt insufficient to explain its slipperiness?

The idea that pressure alone causes ice to melt is insufficient because the actual pressure exerted by a person on ice skates is not enough to significantly lower the melting point of ice. Moreover, light objects or those with a larger surface area should not slip at all if pressure were the sole factor.

What is the phenomenon known as 'pre-melting'?

Pre-melting is the process that occurs before solid ice melts into liquid water. It involves changes in the mobility of the topmost water molecules on the ice surface as the temperature increases, leading to a change in the slipperiness of the ice.

How does the slipperiness of ice change with temperature?

The slipperiness of ice is temperature-dependent. It is found to be most slippery at around -7°C, which is the typical temperature used in speed skating rinks. As the temperature decreases further, the ice becomes less slippery.

What technique was used by researchers to visualize the surface of ice at the atomic level?

Researchers used an atomic force microscope (AFM) to visualize the surface of ice at the atomic level. This technique is sensitive enough to detect the space between individual atoms and can produce detailed images of the ice's surface.

What did the AFM images reveal about the structure of the ice surface?

The AFM images revealed that the ice surface has a quasi-liquid layer with loosely bound water molecules that are oriented in a disordered manner. These molecules are held by a reduced number of hydrogen bonds and can move with a freedom not usually experienced by a solid.

Why doesn't the AFM tip drag water molecules along as it scans the ice surface?

The AFM tip does not drag water molecules along as it scans the ice surface because the experiment was conducted at a very cold temperature (-150°C), where the slippery water molecules are 'frozen' in place, allowing for a clear image to be captured without the molecules moving around.

Outlines

00:00

🧊 The Mystery of Ice's Slippery Surface

This paragraph delves into the unusual properties of ice, particularly its slipperiness. It discusses the historical debate over why ice behaves this way and introduces the idea that the answer may lie in the molecular behavior at the ice's surface. The script mentions Michael Faraday's experiment in the 1850s, which suggested a thin layer of liquid water could be the cause. However, it also points out that ice remains slippery even in a vacuum, where no liquid layer can form, indicating a more complex explanation is needed.

05:02

🔍 Unveiling the Atomic Secrets of Ice

This section of the script describes the use of an atomic force microscope (AFM) to study the surface of ice at the atomic level. It explains the AFM technique and how it was used to capture the first detailed images of ice's surface. The findings revealed a quasi-liquid layer of loosely bound water molecules at the surface, which are not as tightly structured as those within the bulk of the ice. This discovery provides a new perspective on the slipperiness of ice, suggesting that these molecules can move more freely, contributing to the surface's slipperiness.

10:02

🌡️ Temperature's Role in Ice's Slipperiness

The final paragraph explores how temperature affects the slipperiness of ice. It references a 2018 study that showed ice's slipperiness varies with temperature, being most slippery at around -7°C. The script discusses the concept of 'pre-melting,' where the topmost water molecules gain mobility before the ice melts into liquid water. When a true liquid layer forms, the ice becomes less slippery. The paragraph concludes by emphasizing the complexity of the seemingly simple question of why ice is slippery, highlighting the interplay of solid, quasi-liquid, and liquid states on the ice's surface.

Keywords

💡Ice Fusion

Ice fusion refers to the phenomenon where two blocks of ice momentarily bond to form a single piece. This is a key concept in the video, illustrating the unusual property of ice to stick together when in contact. The script discusses this in the context of the unique slipperiness of ice and how it relates to the molecular behavior on its surface.

💡Slipperiness

Slipperiness is the property of a surface that allows objects to slide over it with minimal friction. In the video, the slipperiness of ice is a central theme, with the script exploring why ice is so slippery, even in the absence of a liquid water layer, and how this relates to its molecular structure and behavior at the surface.

💡Water Molecules

Water molecules, H2O, are the basic units that make up ice. The script delves into the behavior of individual water molecules on the surface of ice, explaining how their arrangement and interaction with each other contribute to the slipperiness of ice. The video mentions how these molecules are loosely bound and can move freely, unlike those within the solid bulk of the ice.

💡Atomic Force Microscope (AFM)

An Atomic Force Microscope (AFM) is a high-resolution imaging tool used to visualize surfaces at the atomic level. The script describes how researchers used an AFM to capture the first detailed images of ice's surface, revealing the molecular orientations and the presence of a quasi-liquid layer that contributes to its slipperiness.

💡Hexagonal Ice (IH)

Hexagonal Ice (IH) is a crystalline form of ice where water molecules are arranged in a hexagonal pattern. The video explains that this is the typical structure of ice, with oxygen molecules facing outward. The script discusses how this structure interfaces with other forms of ice and contributes to the unique properties of the ice surface.

💡Cubic Ice (ICC)

Cubic Ice (ICC) is another form of ice with a cubic crystalline structure. The script mentions the presence of small clusters of this type of ice at the boundaries with hexagonal ice, where the water molecules exhibit a less structured orientation, contributing to the ice's slipperiness.

💡Hydrogen Bonds

Hydrogen bonds are a type of chemical bond that occurs between molecules, particularly in water, where hydrogen atoms form a bond with oxygen atoms of adjacent water molecules. The video explains how the formation and breaking of hydrogen bonds in water molecules contribute to the transition from liquid to solid and affect the surface properties of ice.

💡Pressure Melting

Pressure melting is the process by which ice melts under pressure, lowering its melting point. The script discusses an early hypothesis that the slipperiness of ice could be due to pressure melting creating a thin layer of liquid water on the surface, but this idea is later challenged by the findings of the AFM experiments.

💡Friction

Friction is the resistance that one surface or object encounters when moving over another. The video explores the role of friction in the slipperiness of ice, suggesting that the heat generated from friction between surfaces could contribute to melting the ice and forming a slippery layer. However, it also questions this theory based on the observed behavior of ice under different conditions.

💡Pre-melting

Pre-melting is the process that occurs before solid ice melts into liquid water, where the surface of the ice becomes more mobile and slippery. The script explains how this process is temperature-dependent and contributes to the unique slipperiness of ice, with the slipperiness being maximum at a certain temperature, as revealed by the 2018 research paper mentioned.

💡Quasi-liquid Layer

A quasi-liquid layer is a thin surface layer of a solid material that behaves like a liquid due to its loosely bound molecules. The video describes how the AFM images revealed the presence of such a layer on the surface of ice, which is believed to be responsible for its slipperiness. This layer is not as structured as the solid ice beneath it and can move more freely, contributing to the unique sliding properties of ice.

Highlights

Ice's unusual property of fusing two blocks together briefly is more complex than it seems.

The slipperiness of ice has been a subject of debate for a long time.

Researchers have used an atomic force microscope (AFM) to visualize the ice surface at an unprecedented level of detail.

The traditional theory that a thin layer of liquid water on ice causes slipperiness has been challenged.

Experiments under extreme vacuum conditions show that ice remains slippery even without a liquid layer.

The unique property of water being denser as a liquid than as a solid was discussed in the context of ice's behavior.

James Thompson's work on the relationship between freezing temperature and atmospheric pressure was highlighted.

The idea that pressure from ice skates melts the ice surface to create a slippery layer was proposed but later questioned.

Experiments show that the slipperiness of ice is not solely due to pressure-induced melting.

Heat generated from friction between surfaces is suggested as a possible cause for ice's slipperiness.

Researchers discovered a quasi-liquid layer on the surface of ice that behaves differently from both solid and liquid states.

The atomic force microscope (AFM) is described as an instrument capable of sensing individual atoms.

The surface of ice at -150°C was found to have a structure with loosely bound molecules that contribute to its slipperiness.

An increase in temperature leads to a change in the mobility of the topmost water molecules on the ice surface.

The slipperiness of ice is maximized at -7°C, the typical temperature used in speed skating rinks.

The video concludes that the slipperiness of ice is due to its unique quasi-liquid surface layer.

The video raises the question of the origin of gold as another simple question with a complex answer.

Transcripts

ice is weird just by holding together

two blocks of ice only for a second they

fuse to become a single object this as a

property of solids is reasonably

uncommon at least in my experience so

how is this possible let me know what

you think but the answer is more

complicated than it seems and it relates

to another strange property of ice that

occurs at its surface it's seemingly

unreasonable level of slipperiness

me just enjoying a freeze is coming we

have been debating the quirks of Ice's

surface for a long time but to get a

good understanding of it you really want

to be able to see what the individual

water molecules are doing this sounds

obviously like it should be impossible

and it has been until now the research

team has just released their findings in

the scientific journal Nature collected

using a technique that is so sensitive

it can feel the space between individual

atoms and produce for the very first

time a picture of Ice's surface but to

really understand what this picture

tells us and why ice is slippery we need

to Rewind by about 160

years on its surface ice being slippery

makes sense when water is spilled on the

floor it becomes a slip Hazard we reason

this is because water creates a mobile

barrier between our foot and the floor

almost just like stepping on a bunch of

marbles that tumble along and cause you

to slip you might guess maybe ice is so

slippery because it too is covered in a

thin layer of liquid water maybe the

answer is as simple as that in fact in

the late 1850s Michael Faraday one of

the most influential scientists in

history particularly across

electromagnetism electrochemistry tried

this exact experiment and concluded the

very same thing which he announced in a

talk at the Royal Society however there

is a problem with this theory if you can

conduct this experiment under extreme

vacuum where no liquid layer can be

present because liquid water molecules

would have evaporated away as there is

no atmosphere holding them down then Ice

Still Remains slippery so what's

actually

[Music]

happening believe it or not ice science

was all the rage through the mid 1800s

to early 1900s partially inspired by the

other observation we've all made water

as a liquid is denser than water as a

solid which which is why ice floats on

liquid water this it turns out is a

really rare property across materials

with bismuth being one of the very few

similar exceptions for water this is the

result of the crystal structure water

forms as it freezes the hydrogen bonds

that rapidly connect and disconnect from

nearby Neighbors in liquid water as it

begins to freeze the molecules of H2O

arrange to form bonds in such a way they

create additional space between the

molecules so the same volume of water

expands by about 10% as it goes from

liquid to solid in the 1850s James

Thompson an Irish mathematician and

engineer was examining the change from

liquid to solid and noticed that the

freezing temperature changed based on

atmospheric pressure Thompson was one of

The Inspirations of the field of

thermodynamics something I'll never

personally forgive him for but his work

did lead us to developing this useful if

somewhat complicated looking phase

diagram of water's Behavior here we see

what Thompson saw we can cause ice to

melt and become water either by

increasing the temperature or by

increasing the pressure maybe ice can be

slippery in a vacuum even if it's liquid

layer evaporates away because as soon as

we go to touch it to measure its

slipperiness the pressure of that touch

melts the surface and creates a newly

slippery liquid layer in 1886 John Jolie

followed the same reasoning to suggest

how ice skaters might Glide across

frozen lakes Jolie suggested that the

pressure of a thin ice skates blade is

so great because it touches ice on such

a small area that it melts the ice to

water creating a slipping layer in

theory a good suggestion earning him the

nickname John Bon Jolie however while

the basic idea is correct you can melt

ice by pressurizing it the numbers don't

really work at all 150 lb person

standing on Ice wearing a pair of ice

skates exerts a pressure of roughly 50

lb per square in on the ice that amount

of pressure lowers the melting

temperature from 0 to -0.01

16666 repeating de C or for Americans

32° F down to 31.9 7° fah if this

explanation was in fact correct light

objects or ones with large surface area

like a hockey park or a ski would create

even lower pressure and shouldn't slip

at all and that's a problem because in

fact we see the exact opposite many

winter sports are best below freezing

temperature figure skaters prefer - 5.5

de C for a slower softer ice to land

their tricks on whereas hockey players

like the cold hard and fast conditions

of - 9° c speed skaters like somewhere

in between at -7° C this is also

disproved as a primary mechanism by our

first experiment when we press two

blocks of ice together they freeze why

would an ice skate against ice become

slippery but ice against ice freezes

despite this hypothesis's shortcomings

it Remains the dominant EXP of

slipperiness of ice for over a century

including many YouTube videos about it

so if pressure is not responsible what

else could be maybe it's heat generated

from

friction two surfaces in contact moving

relative to each other produce heat

could this heat be melting the ice to

form the slippery liquid layer now this

will of course happen to some extent but

most practical experience tells us we

don't have to be moving much to slip

instead it feels very much like the

phenomenon that is producing this

slipping is already present without

pressure and without friction and

without heating being required if this

idea of a liquid water layer can't fully

explain why ice is so slippery maybe

it's something that behaves like a

liquid but isn't one and isn't a solid

either when we described the freezing of

water into ice we talked about the

hydrogen bonds aligning within the bulk

material to create a solid less dense

than the liquid phase all of the

molecules were held in rigid formation

supported by the network of surrounding

molecules which are similarly locked in

position this is true everywhere within

a solid except for at the surface where

the supportive crystal structure extends

below but above the outermost layer of

water molecules interact with nothing

but the atmosphere or whatever object

they come in contact with it was at this

surface that researchers directed their

focus using a piece of equipment called

an atomic Force microscope or AFM which

here is a no expense spared mockup of

one the AFM has a long caner lever about

100 to 500 microns long or about the

length of the diameter of two human

hairs side by side it's about 30 to 50

microns wide which is half of the

diameter of a grain of sand and around

0.5 to 0.8 microns thick which about the

thickness of a red blood cell I used AFM

probes a lot in my PhD and although they

are metal they are so thin that it's

better to think of them as a blade of

grass fluttering on the Wind than a

piece of metal at the end of the canala

there is a tip that is usually

triangular and goes from quite wide at

its base to at its end point just the

width of a single atom You could argue

very reasonably that AFM tips are the

sharpest objects in the world this AFM

probe is attached to the atomic Force

microscope itself which then drags the

probe along the atomic surface of a

material here represented by these

marbles in a tray and it measures or

really feels the change in height of the

tip as it travels over over the surface

of the individual atoms but how do you

sense or feel the bump of going over

just a single atom even though the

height change is absolutely tiny by

reflecting a laser beam off of the back

of the caner lever and detecting the

position of that laser beam a long way

away this amplifies the up and down

motion of the caner lever and allows you

to measure the bump of going over an

atom as well as the gaps in between

atoms on a Surface this produces images

of atoms that look like this the

research team conducted their experiment

at Min

-150° C and in a near perfect vacuum

with at the very tip a single carbon

monoxide molecule under normal

conditions they found that the water

molecules are arranged like this in

layers of hexagons stacked one on top of

the other a phase of ice called IH for

hexagonal ice this ice type typically

features the oxygen molecule of the H2O

facing outward however there are also

small clusters of a secondary ice type

cubic in nature called ICC no pun

intended and the interesting thing

happens at the boundaries between these

two ice phases rather than the neatly

arranged uniform oxygen facing outward

molecular orientation as these two types

of ice don't nicely interface together

there's a perimeter of water molecules

between the two that aren't quite sure

whether to orient in a hexagonal or

cubic structure and so kind of end up

doing their own thing usually pointing

their hydrogen atom outward away from

the Ice's surface this is the very first

time we've been able to image the

surface of ice to this level of detail

and see exactly the orientations of the

atoms within the water molecules but

what do these findings actually mean

this break-in structure this disorder

not prevented or tamed like it is deeper

within the solid creates a collection of

loosely bound molecules on the surface

of the ice only held by a reduced number

of hydrogen bonds the suggestion is that

these Loosely bound molecules can move

with freedom not usually experienced by

a solid but aren't quite as free as a

liquid either this quasi liquid layer

May detach and reattach to the surface

acting as we first imagined like a layer

of marbles able to shift and move

creating one of the only solids in the

world that slips but the story is more

complicated still as I looked at these

images there was something that confused

me if you've run an AFM before you'll be

thinking the same thing how do you drag

your AFM tip over something that's

slipping around on the surface during my

PhD I used to image nanop particles on

glass surfaces that I hoped were fixed

in place but sometimes they would detach

and what I would image would be a flat

plane with a sudden and long line in it

as I dragged the atoms along with the

movement of the tip why don't we see

these water molecules slipping around

like the marbles that we described them

to be I had to dig around to find out

but I found a research paper that gives

us a clue back in 2018 a team of

research led by Professor Daniel Bon

from the University of Amsterdam through

macroscopic friction experiments at

temperatures ranging from 0 C to- 100° C

showed that surprisingly ice goes from

extremely slippery as a surface at

around 0° C to a high friction surface

at -100° C this is why the AFM

experiment conducted at an even colder

minus 150 was able to capture such a

clear image it's so cold here the

slippery water molecule marbles are

frozen in place these AFM images also

reveal something else as the researchers

increased the temperature the cubic

phase grew across the surface as a

temperature increased the increased

thermal energy drives a change in the

mobility of the topmost water molecules

this matches the temperature dependence

of the measured change in friction from

that 2018 paper this phenomenon is part

of a process called pre-melting the the

process that happens before solid ice

melts into liquid water and actually

upon melting as soon as a real liquid

layer forms on it it actually becomes

less slippery as the highly structured

solid ice becomes more easily deformed

the experiments in 2018 showed that the

slipperiness of ice is actually at its

maximum at -7° C the temperature

typically used in speed skating rinks

putting this all together this is a very

complicated answer to a very simple

question of why is I slippy it's a solid

with an outermost layer that is free to

move like marbles across its surface

liquid like in nature but actually when

a liquid layer is present that becomes

less slippery than the solid an

incredibly uncommon behavior from one of

the most common materials on

Earth I love that sometimes it's the

simplest questions that make us scratch

our heads the hardest if if you like

this video you might be interested in a

similar simple question with an answer

that we actually aren't quite sure about

where does gold actually come from as

always thank you very much for watching

I'll see you next week

goodbye okay do you know how hard it was

to get these two ice cubes to actually

stick together you have to become a

single

block they stick who they to become a

single block my fing fingers are so

cold block they don't they don't stick

what's happening they turn into a