00:00I'm sitting in a hot tub filled to the brim with solid sand.
00:09This is one of the coolest things ever.
00:11If you take a tub of sand like this and then add air in just the right way, it basically
00:16becomes a liquefied soup.
00:47In science, this is known as a fluidized bed.
00:50It's used in industrial applications such as powder coat painting or in grain silos to make sure that the grain
00:56flows smoothly to the outlet.
01:07With air on, the top surface is nearly frictionless. It's like an air hockey table.
01:15And then when you cut off the air, it freezes everything exactly where it's at.
01:38So today I'm going to show you how to make a simple version like this yourself.
01:41And then because I became curious what it would feel like to be fully immersed in something like this, we
01:46made a hot tub sized version.
01:47As you can see from this 60 year old video from the Royal Institute of Science, this demo isn't exactly
01:51new.
01:52I've wanted to build one for a long time, but you can find literally no information online on how to
01:57make one like that.
01:58So I started combing through a bunch of patent drawings for massive industrial sized fluid beds.
02:02And I noticed that instead of one big inlet, they all had a bunch of small holes to deliver the
02:08air.
02:08So starting with that in mind, it still took us 25 failed versions before we arrived at this design.
02:14As you can see, it's just a bunch of half inch PVC pipes arranged sort of in a ladder.
02:19But the key is to drill two one millimeter holes 90 degrees apart from each other.
02:24And then do a bunch of those spaced 25 millimeters apart.
02:27Then you glue all the pipes together and just make sure you orient the holes down so that will keep
02:31the sand from getting in.
02:33And then you just seal off the container with some hot glue.
02:35And then fill your container with either fine sand or we found glass beads worked really well.
02:39And you can power with a small air compressor like this or you could just rent a large nitrogen container
02:43like this for about 30 bucks.
02:45And that'll give you 10 minutes of run time.
02:46So my buddy Ken had an old broken spa in his backyard, which we decided to put to good use.
03:11It just stops. And you're like locked in place. It's like a weighted blanket on every surface of your body.
03:18Oh!
03:20Oh!
03:21Oh!
03:29Oh!
03:30Oh!
03:35Oh!
03:38Oh!
03:39Oh!
03:46Now that it was tested and ready,
03:48in my ongoing quest to be the favorite uncle,
03:51.
03:53I decided to surprise my nephews with it
04:13But before we get to swimming in sand let's talk about the science behind a fluidized bed
04:18And we don't click away if you think science is boring if you're new here
04:21You should know that my approach to science is similar to velociraptor hunting patterns
04:25I try to bring people in with a catchy thumbnail or a cool thing to see and then when they
04:29least expect it
04:30I'm gonna leave the analogy breaks down a little at the end
04:32But if you promise to hang with me for the next two minutes
04:34I promise to try and walk the delicate line between trying to make things simple to understand without oversimplifying or
04:40being condescending
04:41Fluidization is just when you have enough upward air so that the force of the air pushing on each grain
04:46of sand
04:47Is equal to the downward force of gravity or weight and when that happens on any individual grain of sand
04:52It hovers in equilibrium like this you can think of forces acting on an object like a tug-of-war
04:58If an object is in equilibrium
05:00That means there's a tie and it doesn't accelerate in either direction
05:03Just like in a real tug-of-war if the sides are even however if you add Stone Cold Steve
05:08Austin to this side
05:09That will make it totally unbalanced and will start to move this way
05:12Which is actually what happens if you accidentally turn the air up too high
05:16And so fluidization occurs in that sweet spot where the sand particles hover in equilibrium
05:20Which makes them easy to move around
05:21This is also the reason sometimes you'll see pools pumped with air to cushion the landing for the divers
05:27Then you notice that some stuff floats in the sand and other stuff sinks
05:30This has to do with the buoyancy force which is a function of the density of the surrounding fluid and
05:36the volume of the object itself
05:38Whenever an object exists in a pressure gradient there are forces from pressure pushing in on all sides
05:43But they push a little bit harder the deeper that you are
05:45Which is why it hurts more to be the bottom guy in a dog pile or it hurts your ears
05:50more the deeper you dive in the pool
05:51And this makes sense because the deeper you dive the more water there is above you pushing down
05:56And if you add up the size and direction of all those arrows a bunch of stuff cancels out and
06:00you're left with one net force
06:01Pointing upwards that is the buoyancy force and if your buoyancy force happens to be greater than your force from
06:06gravity
06:07You float and if your buoyancy force happens to be less than the force from gravity you sink now
06:12We usually think of buoyancy with water
06:14But you could think of things like helium balloons being buoyant in our atmosphere
06:18So here's a trick question which of these has a higher buoyancy force. It's actually
06:24The rubber ball
06:25Buoyancy force has nothing to do with the density of the object just the volume
06:29So since the rubber ball takes up more space it has a higher buoyancy force
06:33But you might object then why does the rubber ball sink and the balloon floats?
06:39Remember it's a tug-of-war the rubber ball sinks because the force from gravity on the thick rubber skin
06:44in the air inside is
06:46Bigger than the buoyancy force
06:47But for the balloon even though it doesn't have as big of a buoyancy force compared to the ball
06:52It still floats up because that buoyancy force is bigger than the weight arrow from the helium and the thin
06:57rubber shell
06:58And the helium will keep rising like a ball floating up from deep in a lake
07:01And then it will eventually hang out where the density of the atmosphere is roughly equal to the density of
07:06the helium in the balloon
07:07Because that's where the tug-of-war becomes equal
07:09We made it through now back to my nephews
07:39And everybody starts to move as soon as Paca Paca starts to move
07:49Oh no, I can't get it out
07:52You can't get it
07:52Get it
07:53I can't
07:54Got it
08:13I can't get it
08:18I can't get it
08:24Okay cut it
08:24inせて
09:14You
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