We FINALLY Proved Why Ice Is Slippery
Summary
TLDR视频脚本探讨了冰的奇特性质:冰的表面异常滑,以及冰块如何短暂地融合成一体。通过原子力显微镜(AFM)的先进技术,研究者首次揭示了冰表面的分子结构。发现冰的表面存在一种类似液体的松散分子层,这可能是冰滑的主要原因。视频还讨论了历史上关于冰滑性的误解和现代研究的发现,解释了冰在不同温度下摩擦系数的变化,以及冰的“预熔”现象,为理解冰的滑性提供了复杂的科学解释。
Takeaways
- 🧊 冰的表面具有独特的滑性,这与固体的一般性质不同。
- 🔍 科学家使用原子力显微镜(AFM)首次观察到冰表面的分子结构。
- 📚 历史上,人们曾认为冰的滑性是因为表面覆盖了一层液态水。
- 🚫 然而,在极端真空条件下,即使没有液态水层,冰仍然保持滑性。
- 🔬 研究发现冰的表面分子结构与内部不同,表面分子排列较为松散。
- 🔄 冰的表面存在一种类似液态的层,但并非真正的液态,这可能是滑性的原因。
- 🌡️ 冰的滑性与温度有关,研究发现在-7°C时滑性最强。
- 🤔 冰的滑性可能与表面分子的自由度有关,这些分子仅通过较少的氢键连接。
- 🏒 冰的滑性对冬季运动有重要影响,不同运动对冰面温度有不同的偏好。
- 🔄 冰的表面在不同温度下会经历结构变化,这影响了其滑性。
- 🌍 冰的这种不寻常的物理行为是地球上最常见的材料之一的独特特性。
Q & A
为什么冰块能够在短时间内粘在一起变成一个单一物体?
-冰块在短时间内粘在一起是因为冰的表面分子具有较低的结合力,可以形成一种准液态层,这使得冰块在接触时能够暂时粘附。
冰的表面为什么特别滑?
-冰的表面特别滑是因为在冰的外层存在一种准液态层,这层分子的结合力较弱,可以自由移动,类似于在冰面上滑动的弹珠。
科学家是如何观察到冰分子的表面结构的?
-科学家使用原子力显微镜(AFM)这种极其灵敏的技术,能够感知到单个原子之间的空间,从而首次获得了冰表面结构的图像。
为什么在极端真空条件下,冰仍然保持滑性?
-即使在没有液体水分子的极端真空条件下,冰仍然保持滑性,这是因为冰的表面存在一种由分子结构不规律造成的准液态层。
历史上有哪些科学家尝试解释冰的滑性?
-历史上,包括迈克尔·法拉第(Michael Faraday)和约翰·乔利(John Joly)在内的科学家都曾尝试通过实验来解释冰的滑性。
为什么冰在压力作用下会融化形成滑层,但两块冰相互接触时却会冻结?
-冰在压力作用下会融化形成滑层是因为压力降低了冰的熔点,但在两块冰相互接触时,由于没有足够的压力来降低熔点,它们会因为表面分子的结合而冻结。
冰的滑性是否与摩擦产生的热量有关?
-虽然摩擦会产生热量,可能导致冰融化形成滑层,但实际经验表明,即使在没有明显运动的情况下,冰也会滑,这表明冰的滑性可能与更深层次的分子结构有关。
原子力显微镜(AFM)是如何工作的?
-AFM通过一个极细的探针在材料表面移动,利用激光反射来放大探针的微小运动,从而测量探针尖端在原子层面上的高低变化,生成材料表面的原子级图像。
冰的表面分子是如何排列的?
-冰的表面分子通常以六角形层状排列,形成一种称为IH的冰相,但在不同冰相的交界处,分子的排列较为混乱,指向外部的氢原子较多。
冰的滑性是否与温度有关?
-是的,冰的滑性与温度有关。在2018年的实验中发现,冰在-7°C时滑性最大,这也是速滑冰场通常使用的温度。
为什么冰在-100°C时的摩擦力会增加?
-在极低温度下,冰表面的准液态层分子运动减缓,导致冰的表面变得更加坚硬,摩擦力因此增加。
Outlines
🧊 冰的奇异性质
本段介绍了冰的两个不寻常的特性:其表面异常滑和冰块能瞬间融合。传统上认为冰滑是因为表面有一层液态水,但实验显示即使在真空中,冰依然滑。19世纪的科学家们通过实验和理论探讨了冰的这些特性,包括水分子在冰中的排列方式以及冰的密度为何低于液态水。此外,还提到了大气压力对冰熔点的影响以及冰在不同压力和温度下的行为。
🔬 原子力显微镜下的冰表面
科学家们使用原子力显微镜(AFM)首次观察到冰表面的分子结构。在极低温和真空条件下,发现冰表面存在一种准液态层,由松散结合的水分子组成,这些分子不像固体那样固定,也不像液体那样自由。这种结构在冰的两种相——六角冰(IH)和立方冰(IC)——的交界处尤为明显,这些分子的氢原子通常向外指向,可能与冰的滑性有关。此外,还讨论了温度如何影响冰的滑性,以及冰在不同温度下摩擦系数的变化。
🌡️ 冰的滑性与温度的关系
本段深入探讨了冰的滑性与其表面分子结构和温度的关系。2018年的研究表明,冰在0°C时非常滑,但在-100°C时摩擦力增大。这解释了为何在极低温度下AFM能捕捉到清晰的冰表面图像。随着温度的升高,冰表面的立方相(IC)增长,水分子的移动性增加,这与摩擦系数的变化相匹配。冰的滑性在-7°C时达到最大,这与速度滑冰场地的温度一致。视频最后提出了一个关于冰滑性的复杂答案:冰是一种固体,但其表面有一层可以像弹珠一样移动的分子,这种特性在自然界中极为罕见。
Mindmap
Keywords
💡冰的粘接性
💡滑性
💡原子力显微镜(AFM)
💡水分子
💡氢键
💡冰的表面结构
💡准液态层
💡压力熔化
💡摩擦
💡预熔
💡温度依赖性
Highlights
冰块的粘附现象:冰块在接触时能够短暂地融合成单个物体。
冰的表面异常滑:冰的滑性与固体的一般性质不同,其表面滑性令人费解。
原子力显微镜(AFM)的使用:研究团队利用AFM技术首次观察到冰的表面分子排列。
冰的滑性与水分子的排列:水分子在冰表面形成非规则排列,可能与冰的滑性有关。
冰的表面分子结构:冰表面存在六角形和立方体两种冰相的分子。
冰的表面分子动态:表面水分子由于氢键数量减少而具有较高的活动性。
冰的滑性与温度的关系:冰在-7°C时滑性最大,这与速滑运动中使用的温度一致。
冰的表面分子的准液态层:表面分子可能形成一种介于固体和液体之间的状态。
冰的滑性与压力的关系:压力对冰的滑性影响有限,与之前的理论不符。
冰的滑性与摩擦的关系:摩擦产生的热量并不能完全解释冰的滑性。
冰的表面分子的动态变化:温度升高时,冰表面分子的排列和活动性发生变化。
冰的表面分子的非均匀性:冰表面分子的排列在不同区域存在差异。
冰的滑性与液态水层的关系:液态水层的存在可能使冰的滑性降低。
冰的表面分子的动态模拟:通过AFM技术观察到冰表面分子的动态行为。
冰的滑性与冰相变化的关系:冰的滑性可能与冰的相变过程有关。
冰的表面分子的排列对滑性的影响:冰表面分子的非规则排列可能是滑性的关键。
冰的滑性的复杂性:冰的滑性是一个涉及多种因素的复杂现象。
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
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