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elise drop to the bvk check on of
time family of stephen king road dates
is true equation would have the same
especially for American audiences
acquisitions
my daughter at aida
it worked very well was to ida
schooled last September
since that day keeping us a head to
daily head to revise the
lessons of the day eventually
revised only prepare that of the
next day
at first everything was new to her
the numbers the letters the words but
the most important the concepts so the
days are linked and difficulties
to find simple explanations and
clear also once in the book
scientific education and
technology
yes I assure you it exists is there
where there was a question of defining
two states of matter you have fun
you imagine for a child of 5 years the
question was what a solid
what is a liquid and in the book
the definition said that an object and 18
liters
if I can hold in my hand it is
the team in the opposite case as much
that physicist I found this
simple definition of efficiency
formidable
but deep down I know she’s vague
and therefore imprecise to test this
definition
I came here today for you
ask a question here it is
sand is what it is solid or
liquid
Yes
you’re right the answer to this
question is not simple
and I guess the book designer
certainly does not think of
sands when he brought this
definition there to meet the
question
I brought sand with us
let’s do an experiment that we can
very well to do with the mind what
say the Germans they say guide
external is an experiment with
the spirit but that you can do at home
you at home his problem if we
pour sand on a table the sand goes
to deposit to form a deposit that
will be perfectly balanced
unlike the water they get
would put horizontally
this deposit of sand is called a pile
can even support a load like a
strong fellow
now if I include the table the sand
will flow like a liquid so this
ability to be both strong and
team
know that this is not a
specificity of sand alone but in fact
it’s a general characteristic of
all members of a large family
that we call the material in bold or
well the granular materials the
granular materials are actually
omnipresent in our daily lives and
even at the universe level
Here are some examples
it can be powdered sugar or
parts
it can be rice it can be
money for siobhan it can be
couscous of the balcony crisis it can be
all the pulses in fact all the
dried fruits but not only
the granular material can present itself
in the form of pharmaceutical powder
gravel ballast for railways
tired for railroad but also that
can be the material of which is composed
the ones of this here in algeria where on
the planet mars or even the matter
which consists of canceling the rings of
Saturn
so in fact the material in grains
it is ubiquitous everywhere even in
geophysics and even in astronomy so
the understanding of these environments
granular is actually engaging a game
socio-economic and industrial
is very important at the beginning this
science was stayed during
for a long time the privilege of engineers and
geophysicists but since one
twenty years the material in bold
has become the playground for a
number of physicists of which I
be part of it so you would not say but
why this sudden craze for the
matter in bold for physicists who
usually deals with issues
fundamental
but actually to matter in bold it
arouses curiosity
it poses problems and challenges
in fact it even jeopardizes
physical theories that smells very well
established the physical science of the
granular material is somehow
hybrid meaning
she lies astride physics
statistical
mechanics is about the physics of
messy backgrounds but it takes
know that for a long time the man has
understood that cool sand like the
team
At first we had water clock
called the clepsydra and very
quickly they left their place or
hourglass and this for a very good
reason the flow of grains in the
Hourglass is constant and regular
unlike the flow of water in the
clepsydra that will decrease when the
water level in the upper part
of the clepsydra will diminish what is this
happening in the hourglass at the level
throttling actually the grains at this
level there only feel the pressure
layers and neighbors but really
very close neighbors and all the weight of
upper layers and directed
laterally
with what is called scale of
force or networks
contact this is called the
deadlines made of vault which is very
well known in civil engineering good I
chose an image the alhambra here so we
see arches and vaults
so this arch effect
in fact it can be used to good
for example to reduce by one
drastically the pressure that can
exert the weight of a train on
rails and railway sleepers
that’s why we use ballast
but still this effect darche
maybe pernicious and the cause of not
bad damage
if I take for example the case of a
grain silo if the side walls
are not reinforced they can
experience local pressures very
important and wife and thereby
damages
so to convince you a little of this
arch effect
I will once again invite you to
to do with me just with the mind
some experiences that you can
do your brothers and sisters with care
be with your children at the first
time I saw this experience
it was fire stone gilles de gennes who
did that the university of
strasbourg
so let’s take a glass test tube
filled without half with sand
dry and fine now given a few
taps on the green to compact the
sand is returned the test tube meaning
upside down
surprise the sand will not sink
why because in fact there is a
species of darche that will form with the
fat that will prevent the grain from flowing
the second experience always
impressive is the next if you
take a turbo a cylinder fast in
where you hold a stick
filled with wood is the tube with
fine sand and dry give shots on the
tube to compact the sand is
now try to remove the wing
vertically you will see that these prices
so-called son
even impossible to do one for
arnold schwarzenegger this looks like
many you may have all done
this experience
when you tried to remove the
foot of a beach umbrella when
you have it in French early in the morning
let’s go back now a bit to our
dear hourglasses if we look at the
bottom of the hourglass sand
when cool for those dropped
he does not get horizontal like
I said it just now as a
liquid at equilibrium
in fact they form a camp
revolution with an apex angle that
is very well defined this pile form
in fact totally
autonomous
it is formed from the estate
of avalanches is actually in nature
there was someone who preceded the
physicists of the material in bold there is
can you turn off if he
please light there is what we
call the larva dufour million lalart
dufour millions actually what is this
that she does in the understanding actually the
operation of avalanches she
builds a trap
ruthless of whom an ant we
going out actually saved that trap and the
shape of a hole with a slope that
find in the state of equilibrium
metastable or critical
when an ant passes by the
hole the larva what is she doing there
it is enough that it projects a few grains
sand on the slope and triggered a
avalanche that will result
inexorably the ant goes to the worm
the hole that’s in nature
always with experiences
fantastic with the grain material
I invite you to do another
experience at home that costs nothing of the
all take a bowl
weather make two or three nuts and
completed with laws are or even
chickpeas
now what are you going to do is
that you’re going to shake vertically the
bowl or give you small
taps underneath long enough
and what are you going to notice
you’ll see that nuts that was
child is inside the heap
they will go up alone when by
magic on the surface and in addition to that
they are going to aggregate they are going to
put this effect together we call it
the segregation
good it’s not very pretty but it’s the
case to say it
then the phenomenon of these big of
segregation is first and foremost
contradiction with the second principle of
thermodynamics
why because the more you will try
stir the bowl to mix
the set of laws that is to say
introduce disorder
what happens is the laws
separate there is order that is
form
so you see all the challenge we have
with the physics of fat and so this
phenomenon of segregation it is necessary
know that it can be very pernicious
for a very large number
industrial applications
if we take for example the Ariane rocket
its fuel
it’s not liquid it’s a mixture
of powder so when we go the
transport if the path is not good
tarred ie it can there
to have asperities or holes so
the vibrations what are they going
do they will separate the powders the
mixture of powders in different
chickens and that that can lead to
malfunction in takeoff from
the rocket
now I invite you to leave the
cooking to go for a stroll
seaside and there when you
walk on the wet sand what is it
that you notice you noticed that
you can turn off please
you noticed that under your foot the
it’s dry
we can see it here
in fact what happens when
you
exert pressure with your weight
on the wet sand
the ol is absorbed it is sucked in
instead of being expelled and that’s
exactly the opposite effect of one and
always leans on a beach you have
probably all experienced after a
running session or a match of
foot on the sand a very big
tired
this is probably not due to the
sporty outfit that you chose but
in fact the explanation she is very
simple is that the sand like
all granular media hundred of
highly dissipative systems
in other words the friction forces
and shocks between fat
engulf all the energy you
can put in this type of system
you know that Algeria is
covered more than 80% of the desert
of 2 million kilometers
squares and there it is its properties
Extraordinary Bold Matter
becomes even more so in the sahara the
pile of sand in the desert
call it a dune
you have to know that the dunes do not smell
unique
it’s like human beings and she
is of a crescent form that
what are called barkhanes is
gone from a giant in the form of a
star went the long line that we
calls safe for sword but it’s
one must also know that it is the
living entities in their own right because
that she is born they grow up and she
moves with the winds and more
that the dunes she sings
yes yes you hear the dunes
sings with a powerful voice and
harmonious besides you can
ask the Bedouins in the south who
know these dune fields
they will tell you that in fact that meaning the
jeans do not have pants and jinn
the spirits that populate the countries
vast of the desert that are behind and
who are at the origin of these songs
bewitching
so you see now and you
know that the material in bold causes the
curiosity in present by introducing himself
with properties totally against
intuitive and until today we
we have a lot of trouble explaining
these phenomena related to matter in
fat but egypt ancient for example
the building engineers used the
sand in their works with a very
great mastery not only they have
invented the mortar but also used
sand to erect large
obelisk by dragging them into
silos filled with sand when life
according to he also knew he was
much easier to displaced from
great monuments like on this euro
glyphs it’s easier to move
the great monuments by making them
dishes slide on benches on which
in May a sand that is neither too dry nor
too wet then until today
there is no one who has been able to develop a
general theory or a theory
analytic in which we explain
all these strange phenomena in a
same format read as it is by
example in hydrostatic
hydrodynamic or even in
electromagnetism stone gilles de
gennes nobel prize for physics
the patron saint of liquid crystals a
curious mind towards the end of his
life he brought up to date the
physical and fat science he
said about this one the science
grains is not expensive can
play with sand lentils
putschists scrutinizes everything you
want the grain science is not
expensive but she is very careful
and he also said because matter
disorderly is characterized by a
disorder
he was saying that disorder at scale
microscopic it’s a good animal
erect he is tamed
but the disorder at the scale
macroscopically as is the case in the
matter in bold they require
ij make new explorers so
with a small dose of naivety
we can think that with a shovel a
bucket with funnel
we can propose dpf end project
of study one can frame theses
and then why not relocate his
office and his research laboratory
to put it in a sandbox at
bottom of a kindergarten or in a
desert or beach corner is not it
an instinct that said that play is
perhaps the highest form the
more elaborate research
then sincerely I invite you to
play with sand to have fun with
dry vegetables at home maybe
so tells you so close to the fog
on one of the problematic problems
fundamental physics of today
at the same time you will find
maybe some solutions to stop
the advance of the desert
oh so important for our country
you may even find
solutions to beach erosion and
of weight
but more than that you can even
find solutions to unclog
the monster traffic jams of the
capital alger thank you
[Applause]
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