i'm sitting in a hot tub filled to the
brim with solid sand
this is one of the coolest things ever
if you take a tub of sand like this
and then add air in just the right way
it basically becomes
a liquefied suit
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do
in science this is known as a fluidized
bed it's used in
industrial applications such as powder
coat painting or in grain silos to make
sure that the grain
flows smoothly to the outlet
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with air on the top surface is nearly
frictionless it's like an air hockey
table
and then when you cut off the air it
freezes everything exactly where it's at
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so today i'm going to show you how to
make a simple version like this yourself
and then because i became curious what
it would feel like to be fully immersed
in something like this
we made a hot tub size version as you
can see from the 60 year old video from
the royal institute of science
this demo isn't exactly new i've wanted
to build one for a long time
but you can find literally no
information online on how to make one
like that so i started combing through a
bunch of patent drawings for massive
industrial size fluid beds and i noticed
that instead of one big
inlet they all had a bunch of small
holes to deliver the air
so starting with that in mind it still
took us 25 failed versions before we
arrived at this design
as you can see it's just a bunch of half
inch pvc pipes arranged sort of
in a ladder but the key is to drill two
one millimeter holes
90 degrees apart from each other and
then do a bunch of those
spaced 25 millimeters apart then you
glue all the pipes together and just
make sure you orient the holes down so
that will keep the sand from getting in
and then you just seal off the container
with some hot glue and then fill your
container with either
fine sand or we found glass beads worked
really well and you could power with a
small air compressor like this or you
could just rent a large nitrogen
container like this for about 30 bucks
and that'll give you 10 minutes of run
time as usual i'll put a link to all of
the parts i used the build in the video
description so my buddy ken had an old
broken spa in his backyard which we
decided to put to good use
it just stops and you're like locked in
place
it's like a weighted blanket on every
surface of your body
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um
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now that it was tested and ready in my
ongoing quest to be the favorite uncle
i decided to surprise my nephews with it
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but before we get to swimming in sand
let's talk about the science behind a
fluidized bed and we don't click away if
you think science is boring if you're
new here you should know that my
approach to science is similar to
velociraptor hunting patterns i try to
bring people in with a catchy thumbnail
or a cool thing to see
and then when they least expect it
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clever girl admittedly the analogy
breaks down a little at the end but if
you promise to hang with me for the next
two minutes i promise to try and walk
the delicate line between trying to make
things simple to understand
without oversimplifying or being
condescending fluidization is just when
you have enough
upward air so that the force of the air
pushing on each grain of sand
is equal to the downward force of
gravity or weight and when that happens
on
any individual grain of sand it hovers
in equilibrium like this
you can think of forces acting on an
object like a tug of war
if an object is in equilibrium that
means there's a tie and it doesn't
accelerate in either direction
just like in a real tug of war if the
sides are even however
if you add stone cold steve austin to
this side that will make it totally
unbalanced
and will start to move this way which is
actually what happens if you
accidentally turn the air up too high
as the fluidization occurs in that sweet
spot where the sand particles hover at
equilibrium which makes them easy to
move around
this is also the reason sometimes you'll
see pools pumped with
air to cushion the landing for the
divers now you notice that some stuff
floats in the sand
and other stuff sinks this has to do
with the buoyancy force which is a
function of the density of the
surrounding fluid
and the volume of the object itself
whenever an object
exists in a pressure gradient there are
forces from pressure pushing in on all
sides
but they push a little bit harder the
deeper that you are which is why it
hurts more to be the bottom guy in a dog
pile or it hurts your ears more the
deeper you dive in the pool and this
makes sense because the deeper you dive
the more water there is above you
pushing down and if you add up the size
and direction of all those arrows a
bunch of stuff cancels out and you're
left with one net force pointing upwards
that is the buoyancy force and if your
bouncy force happens to be greater than
your force from gravity you float
and if your buoyancy force happens to be
less than the force from gravity
you sink now we usually think of
buoyancy with water but you could think
of things like helium balloons being
buoyant
in our atmosphere so here's a trick
question which of these
has a higher buoyancy force it's
actually
the rubber ball buoyancy force has
nothing to do with the density of the
object
just the volume so since the rubber ball
takes up more space
it has a higher buoyancy force but you
might object
then why does the rubber ball sink and
the balloon floats
remember it's a tug of war the rubber
ball sinks because the force from
gravity on the thick rubber skin and the
air inside
is bigger than the buoyancy force but
for the balloon
even though it doesn't have as big of a
buoyancy force compared to the ball
it still floats up because that buoyancy
force is bigger than the weight arrow
from the helium
and the thin rubber shell and the helium
will keep rising like a ball floating up
from deep in a lake and then it will
eventually hang out where the density of
the atmosphere
is roughly equal to the density of the
helium of the balloon because that's
where the tug of war becomes equal
we made it through now back to my
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nephews
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my
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as soon
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oh
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okay
thank god
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oh
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you