Are cats liquid? | Marc-Antoine Fardin | TEDxTours
-
0:06 - 0:11I'd like to tell you
something about physics. -
0:12 - 0:17So, it's not exactly the physics
we'd usually see in textbooks. -
0:17 - 0:22Physics is a bit megalomaniac,
it tends to want to govern everything -
0:22 - 0:25from the infinitely small
to the infinitely large. -
0:25 - 0:30So to cover such a broad spectrum,
-
0:30 - 0:33plenty of imagination
is needed, of course, -
0:33 - 0:36because what is happening in an atom,
-
0:36 - 0:40in a grain of sand,
a petanque ball, or a planet, -
0:40 - 0:42isn't necessarily the same thing,
-
0:42 - 0:46so you have to be ready
to invent new laws. -
0:47 - 0:51But in parallel to this approach,
-
0:51 - 0:54knowing how to use some form
of laziness is also necessary -
0:54 - 0:58because what is actually
happening in an atom, -
0:58 - 1:03a grain of sand,
a petanque ball, or a planet, -
1:03 - 1:05can be similar in many ways.
-
1:06 - 1:08And to be able to identify
theses similarities -
1:08 - 1:11between objects that are
at first glance totally different, -
1:11 - 1:14you have to know how to ask
questions that are a bit weird, -
1:14 - 1:17and I have put together a few for you.
-
1:17 - 1:22So what is the commonality between
the break of an uncooked spaghetto -
1:22 - 1:25and the fracture of a metal beam?
-
1:25 - 1:30Or between the vortex that I generate
with my spoon in a cup of coffee -
1:30 - 1:33and hurricanes in the atmosphere?
-
1:33 - 1:36Another one is what is the connection
-
1:36 - 1:40between the physics of accretion
disks around forming stars - -
1:40 - 1:44which is very serious -
and the physics of cake dough? -
1:44 - 1:47Or between mayonnaise on one hand,
-
1:47 - 1:50and nuclear fusion
by confinement on the other? -
1:50 - 1:54Now I'm going to talk about
one of these weird questions tonight, -
1:54 - 1:59that is "What does a liquid ...
-
2:00 - 2:03and a cat have in common?"
-
2:03 - 2:05(Laughter)
-
2:06 - 2:10Obviously behind this question
lies another more serious question that is -
2:10 - 2:12"What is a liquid?"
-
2:12 - 2:17Well, a liquid is a material
that takes the shape of its container -
2:17 - 2:19while maintaining a constant volume.
-
2:19 - 2:22This is the official
definition of a liquid. -
2:23 - 2:25And we see in numerous cases,
-
2:25 - 2:27(Laughter)
-
2:30 - 2:34that cats seem to fit
this definition pretty well. -
2:34 - 2:38They adapt their shape to their container.
-
2:38 - 2:40Maybe you've already seen
pictures like these. -
2:41 - 2:44Quite a lot of these have been circulating
on the internet for many years. -
2:44 - 2:48And, well, I spend a bit
of my time on the internet, -
2:48 - 2:50as a researcher, I mean!
-
2:50 - 2:52(Laughter)
-
2:52 - 2:55And I didn't miss
the appearance of this meme, -
2:55 - 2:59plenty of pictures related
to the question "Are cats liquid?" -
3:00 - 3:03Now several years ago,
-
3:03 - 3:06on a spring afternoon
-
3:06 - 3:10that wasn't motivating me
to do what I was supposed to do, -
3:10 - 3:13I decided to write a scientific
article with the title: -
3:13 - 3:17"On the rheology of cats"
in order to take this question seriously. -
3:17 - 3:20This procrastination actually
led to a bit of success -
3:20 - 3:26since a few years later,
it won me the Ig Nobel prize of physics -
3:26 - 3:29which rewards research that makes
people both laugh and ponder. -
3:30 - 3:34I said that this scientific article
was called "On the rheology of cats," -
3:34 - 3:36but what does "rheology" mean?
-
3:36 - 3:41Rheology comes from the greek
"rheo" which means to flow. -
3:41 - 3:46This same root is found in other words
such as "rhythm" for example, -
3:46 - 3:50or more pompous words
such as "logorrhea" - -
3:50 - 3:53I'm going to try not to do that myself -
-
3:53 - 3:56and some slightly less
pompous words such as"diarrhea," -
3:56 - 3:59everyone knows that one! (Laughter)
-
3:59 - 4:03So the idea was to take
the question "Are cats liquid?" -
4:03 - 4:09and use it to illustrate several issues
that are quite serious this time, -
4:09 - 4:13that rheologists face
and try to solve every day. -
4:15 - 4:19But anyway, are cats liquid or not?
-
4:20 - 4:26In fact, the key is
that the answer to this question -
4:26 - 4:30depends on the span of time
we're ready to allow it. -
4:33 - 4:37Because if we look carefully
at the definition of a liquid, -
4:37 - 4:43"adapting one's shape" is an action
that isn't going to happen instantly. -
4:43 - 4:47Behind this adaptation,
there's a characteristic time, -
4:48 - 4:50and this characteristic time
-
4:50 - 4:53(Laughter)
-
4:53 - 4:55is called the "relaxation time".
-
4:55 - 5:01In many cases - the cases
that are easiest to deal with - -
5:01 - 5:04the relaxation time is something
intrinsic to the material. -
5:04 - 5:09So in the case of a cat,
it will depend on its age or its breed. -
5:09 - 5:12Here we see that number 107
looks more liquid -
5:12 - 5:15and thus has a shorter relaxation time.
-
5:15 - 5:18Because this is precisely the key
behind the concept of relaxation time, -
5:18 - 5:21it's that in reply to the question
-
5:21 - 5:24"Is a cat liquid?" or "Is such
and such material liquid?", -
5:24 - 5:28you must answer another question that is
"What is this material's relaxation time?" -
5:28 - 5:31So for a cat, same thing,
we will ask this question, -
5:31 - 5:34"what is the relaxation time of a cat,
what does it depend on?" -
5:34 - 5:37Here I've chosen a case,
the easiest to deal with, -
5:37 - 5:40when the time of relaxation
only depends on the material itself. -
5:40 - 5:44But it can also depend on the container
-
5:44 - 5:49since we can easily imagine
that a cat relaxes more easily, -
5:49 - 5:53liquefies more easily on the lap
of its owner than in a cage. -
5:54 - 5:58Now, let me give you another
example, that of a drop of water. -
5:58 - 6:00Water is the liquid par excellence.
-
6:00 - 6:03We tend to expect it to spread
on any kind of surface, -
6:03 - 6:07but in some contexts,
we see that water forms droplets. -
6:07 - 6:12Now trying to better understand
why in some cases -
6:12 - 6:18the material flows whereas in others
it doesn't depending on the container, -
6:18 - 6:23relates to questions that imply
research on what we call "wetting". -
6:23 - 6:26And research on wetting
-
6:26 - 6:30includes everything from the development
of super water-resistant windshields -
6:30 - 6:34which circumvent the need
for windshield wipers, -
6:34 - 6:40to research that attempt to understand
the development of cancerous tumors -
6:40 - 6:45because actually, the way
cancerous cells and tissues spread -
6:45 - 6:47can also be understood in this manner.
-
6:47 - 6:52In fact, trying to estimate,
-
6:52 - 6:56to measure, calculate, maybe even modify
-
6:56 - 7:00the one or several relaxation times
of the most diverse and varied materials -
7:00 - 7:02is kind of what is at the heart
of rheologists' research. -
7:03 - 7:06And what you need
to try to keep in mind -
7:07 - 7:09is that these relaxation times
-
7:09 - 7:14can last from one millisecond
to millions of years. -
7:14 - 7:18That doesn't take anything
away from the fact -
7:18 - 7:22that if we observe these materials
long enough, we will see them flow. -
7:23 - 7:28One example over a period
of several decades or years, -
7:28 - 7:33you may have notice
that down a sloping road -
7:33 - 7:35the asphalt sometimes forms like bumps.
-
7:35 - 7:40That's because over a period of years,
the asphalt flows down the slope. -
7:40 - 7:41And the same thing can happen
-
7:41 - 7:45with all sorts of construction
materials from concrete to steel, -
7:45 - 7:48and that's why the industries
that manufacture those materials -
7:48 - 7:51spend a lot of money
to better understand their rheology. -
7:51 - 7:56Sometimes, it is microscopic details
that have an enormous impact. -
7:56 - 8:00The collapse of a building
sometimes depends -
8:00 - 8:03on the precise physics
of the grains of sand that make it up. -
8:04 - 8:08And a good example
of this potentially significant impact -
8:08 - 8:12of the microscopic on the macroscopic
is found among firefighters -
8:12 - 8:15who often like to add
tiny filamentary molecules -
8:15 - 8:18in small quantities, to their water tanks,
-
8:18 - 8:24and these filamentary molecules help
reduce turbulence inside the fire hoses, -
8:24 - 8:29thereby allowing them to spray
the water farther with the same power. -
8:29 - 8:32Now the solutions that rheologists
create for various problems -
8:32 - 8:35are sometimes rather odd.
-
8:35 - 8:38You may have seen in public buildings -
-
8:38 - 8:42not here I think
but in recent public buildings - -
8:42 - 8:45big columns situated
in front of the emergency exits. -
8:46 - 8:47Well, we may think it's a little weird,
-
8:47 - 8:50but actually rheologists have shown
that when a crowd moves, -
8:50 - 8:55these columns tend to reduce
congestion and jams at the exit. -
8:56 - 8:58So in reality,
-
8:58 - 9:02if we wait long enough
-
9:02 - 9:03everything flows.
-
9:03 - 9:06That's the motto of rheology.
-
9:06 - 9:11Even the materials that we walk on
and we usually consider to be solid, -
9:11 - 9:13even those materials flows.
-
9:13 - 9:18So if we take a glacier, for example,
over several decades - -
9:18 - 9:20and that's what
some scientists are doing -
9:20 - 9:24by observing glaciers
with timelapse cameras - -
9:24 - 9:27we can see the ice flowing
into the valley. -
9:27 - 9:31And if we had the chance
to wait millions of years, -
9:31 - 9:34we would see the same thing
happening to mountains, -
9:34 - 9:38and we would see
that peaks and valleys -
9:38 - 9:42are like the crests and troughs
of an ever-moving ocean. -
9:42 - 9:44Alright!
-
9:44 - 9:50Now you may ask again
"But are cats liquid or not?" -
9:51 - 9:56So, my advice is just wait a little bit
-
9:56 - 9:59before giving your final answer.
(Laughter) -
9:59 - 10:01Thank you.
-
10:01 - 10:04(Applause)
- Title:
- Are cats liquid? | Marc-Antoine Fardin | TEDxTours
- Description:
-
Marc-Antoine Fardin sheds light on a discipline that is little known among the general public: rheology, the study of the resistance of material to stress and distortion such as the flowing of substances, be they cells, tissues, polymers or ... cats. Cats? Can these little felines be liquid?
Marc-Antoine Fardin is a physicist and researcher at the French National Center for Scientific Research (CNRS) at the Jacques Monod Institute of the University of Paris Diderot. He was awarded the Ig Nobel Prize that recognizes quirky and even farcical scientific research that nevertheless provokes thought.
This talk was given at a TEDx event using the TED conference format but independently organized by a local community. Learn more at https://www.ted.com/tedx
- Video Language:
- French
- Team:
closed TED
- Project:
- TEDxTalks
- Duration:
- 10:10
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Hélène Vernet approved English subtitles for Les chats sont-ils liquides ? | Marc-Antoine Fardin | TEDxTours | |
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Hélène Vernet edited English subtitles for Les chats sont-ils liquides ? | Marc-Antoine Fardin | TEDxTours | |
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Hélène Vernet edited English subtitles for Les chats sont-ils liquides ? | Marc-Antoine Fardin | TEDxTours | |
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Hélène Vernet accepted English subtitles for Les chats sont-ils liquides ? | Marc-Antoine Fardin | TEDxTours | |
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Hélène Vernet edited English subtitles for Les chats sont-ils liquides ? | Marc-Antoine Fardin | TEDxTours | |
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Hélène Vernet edited English subtitles for Les chats sont-ils liquides ? | Marc-Antoine Fardin | TEDxTours | |
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Hélène Vernet edited English subtitles for Les chats sont-ils liquides ? | Marc-Antoine Fardin | TEDxTours | |
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Hélène Vernet edited English subtitles for Les chats sont-ils liquides ? | Marc-Antoine Fardin | TEDxTours |