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Are cats liquid? | Marc-Antoine Fardin | TEDxTours

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    I'd like to tell you
    something about physics.
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    So, it's not exactly the physics
    we'd usually see in textbooks.
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    Physics is a bit megalomaniac,
    it tends to want to govern everything
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    from the infinitely small
    to the infinitely large.
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    So to cover such a broad spectrum,
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    plenty of imagination
    is needed, of course,
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    because what is happening in an atom,
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    in a grain of sand,
    a petanque ball, or a planet,
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    isn't necessarily the same thing,
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    so you have to be ready
    to invent new laws.
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    But in parallel to this approach,
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    knowing how to use some form
    of laziness is also necessary
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    because what is actually
    happening in an atom,
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    a grain of sand,
    a petanque ball, or a planet,
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    can be similar in many ways.
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    And to be able to identify
    theses similarities
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    between objects that are
    at first glance totally different,
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    you have to know how to ask
    questions that are a bit weird,
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    and I have put together a few for you.
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    So what is the commonality between
    the break of an uncooked spaghetto
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    and the fracture of a metal beam?
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    Or between the vortex that I generate
    with my spoon in a cup of coffee
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    and hurricanes in the atmosphere?
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    Another one is what is the connection
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    between the physics of accretion
    disks around forming stars -
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    which is very serious -
    and the physics of cake dough?
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    Or between mayonnaise on one hand,
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    and nuclear fusion
    by confinement on the other?
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    Now I'm going to talk about
    one of these weird questions tonight,
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    that is "What does a liquid ...
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    and a cat have in common?"
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    (Laughter)
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    Obviously behind this question
    lies another more serious question that is
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    "What is a liquid?"
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    Well, a liquid is a material
    that takes the shape of its container
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    while maintaining a constant volume.
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    This is the official
    definition of a liquid.
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    And we see in numerous cases,
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    (Laughter)
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    that cats seem to fit
    this definition pretty well.
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    They adapt their shape to their container.
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    Maybe you've already seen
    pictures like these.
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    Quite a lot of these have been circulating
    on the internet for many years.
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    And, well, I spend a bit
    of my time on the internet,
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    as a researcher, I mean!
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    (Laughter)
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    And I didn't miss
    the appearance of this meme,
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    plenty of pictures related
    to the question "Are cats liquid?"
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    Now several years ago,
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    on a spring afternoon
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    that wasn't motivating me
    to do what I was supposed to do,
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    I decided to write a scientific
    article with the title:
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    "On the rheology of cats"
    in order to take this question seriously.
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    This procrastination actually
    led to a bit of success
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    since a few years later,
    it won me the Ig Nobel prize of physics
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    which rewards research that makes
    people both laugh and ponder.
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    I said that this scientific article
    was called "On the rheology of cats,"
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    but what does "rheology" mean?
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    Rheology comes from the greek
    "rheo" which means to flow.
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    This same root is found in other words
    such as "rhythm" for example,
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    or more pompous words
    such as "logorrhea" -
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    I'm going to try not to do that myself -
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    and some slightly less
    pompous words such as"diarrhea,"
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    everyone knows that one! (Laughter)
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    So the idea was to take
    the question "Are cats liquid?"
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    and use it to illustrate several issues
    that are quite serious this time,
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    that rheologists face
    and try to solve every day.
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    But anyway, are cats liquid or not?
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    In fact, the key is
    that the answer to this question
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    depends on the span of time
    we're ready to allow it.
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    Because if we look carefully
    at the definition of a liquid,
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    "adapting one's shape" is an action
    that isn't going to happen instantly.
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    Behind this adaptation,
    there's a characteristic time,
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    and this characteristic time
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    (Laughter)
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    is called the "relaxation time".
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    In many cases - the cases
    that are easiest to deal with -
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    the relaxation time is something
    intrinsic to the material.
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    So in the case of a cat,
    it will depend on its age or its breed.
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    Here we see that number 107
    looks more liquid
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    and thus has a shorter relaxation time.
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    Because this is precisely the key
    behind the concept of relaxation time,
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    it's that in reply to the question
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    "Is a cat liquid?" or "Is such
    and such material liquid?",
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    you must answer another question that is
    "What is this material's relaxation time?"
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    So for a cat, same thing,
    we will ask this question,
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    "what is the relaxation time of a cat,
    what does it depend on?"
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    Here I've chosen a case,
    the easiest to deal with,
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    when the time of relaxation
    only depends on the material itself.
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    But it can also depend on the container
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    since we can easily imagine
    that a cat relaxes more easily,
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    liquefies more easily on the lap
    of its owner than in a cage.
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    Now, let me give you another
    example, that of a drop of water.
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    Water is the liquid par excellence.
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    We tend to expect it to spread
    on any kind of surface,
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    but in some contexts,
    we see that water forms droplets.
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    Now trying to better understand
    why in some cases
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    the material flows whereas in others
    it doesn't depending on the container,
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    relates to questions that imply
    research on what we call "wetting".
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    And research on wetting
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    includes everything from the development
    of super water-resistant windshields
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    which circumvent the need
    for windshield wipers,
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    to research that attempt to understand
    the development of cancerous tumors
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    because actually, the way
    cancerous cells and tissues spread
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    can also be understood in this manner.
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    In fact, trying to estimate,
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    to measure, calculate, maybe even modify
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    the one or several relaxation times
    of the most diverse and varied materials
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    is kind of what is at the heart
    of rheologists' research.
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    And what you need
    to try to keep in mind
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    is that these relaxation times
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    can last from one millisecond
    to millions of years.
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    That doesn't take anything
    away from the fact
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    that if we observe these materials
    long enough, we will see them flow.
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    One example over a period
    of several decades or years,
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    you may have notice
    that down a sloping road
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    the asphalt sometimes forms like bumps.
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    That's because over a period of years,
    the asphalt flows down the slope.
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    And the same thing can happen
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    with all sorts of construction
    materials from concrete to steel,
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    and that's why the industries
    that manufacture those materials
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    spend a lot of money
    to better understand their rheology.
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    Sometimes, it is microscopic details
    that have an enormous impact.
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    The collapse of a building
    sometimes depends
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    on the precise physics
    of the grains of sand that make it up.
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    And a good example
    of this potentially significant impact
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    of the microscopic on the macroscopic
    is found among firefighters
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    who often like to add
    tiny filamentary molecules
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    in small quantities, to their water tanks,
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    and these filamentary molecules help
    reduce turbulence inside the fire hoses,
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    thereby allowing them to spray
    the water farther with the same power.
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    Now the solutions that rheologists
    create for various problems
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    are sometimes rather odd.
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    You may have seen in public buildings -
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    not here I think
    but in recent public buildings -
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    big columns situated
    in front of the emergency exits.
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    Well, we may think it's a little weird,
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    but actually rheologists have shown
    that when a crowd moves,
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    these columns tend to reduce
    congestion and jams at the exit.
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    So in reality,
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    if we wait long enough
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    everything flows.
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    That's the motto of rheology.
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    Even the materials that we walk on
    and we usually consider to be solid,
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    even those materials flows.
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    So if we take a glacier, for example,
    over several decades -
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    and that's what
    some scientists are doing
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    by observing glaciers
    with timelapse cameras -
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    we can see the ice flowing
    into the valley.
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    And if we had the chance
    to wait millions of years,
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    we would see the same thing
    happening to mountains,
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    and we would see
    that peaks and valleys
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    are like the crests and troughs
    of an ever-moving ocean.
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    Alright!
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    Now you may ask again
    "But are cats liquid or not?"
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    So, my advice is just wait a little bit
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    before giving your final answer.
    (Laughter)
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    Thank you.
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    (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

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Video Language:
French
Team:
closed TED
Project:
TEDxTalks
Duration:
10:10

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