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,
00:15it basically becomes 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
00:54to make sure that the grain flows smoothly to the outlet.
01:07With air on, the top surface is nearly frictionless.
01:10It'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,
01:45we made a hot tub size version.
01:47As you can see from this 60-year-old video from the Royal Institute of Science,
01:50this demo isn't exactly new.
01:52I've wanted to build one for a long time,
01:54but you can find literally no information online on how to make 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,
02:04they all had a bunch of small holes to deliver the air.
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,
02:28and just make sure you orient the holes down so that will keep the sand from getting in.
02:32And 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 could power with a small air compressor like this,
02:41or you could just rent a large nitrogen container like this for about 30 bucks,
02:45and that'll give you 10 minutes of runtime.
02:46So my buddy Ken had an old broken spa in his backyard,
02:49which we decided to put to good use.
03:11It just stops, and you're like locked in place.
03:15It's like a weighted blanket on every surface of your body.
03:46It's like a little bit of a little more.
03:48in my ongoing quest to be the favorite uncle I decided to surprise my nephews
03:55with it but before we get to swimming in sand let's talk about the science behind
04:17a fluidized bed and we don't click away if you think science is boring if you're new here you
04:21should know that my approach to science is similar to velociraptor hunting patterns I try to bring
04:25people in with a catchy thumbnail or a cool thing to see and then when they least expect it I
04:30mean
04:31the analogy breaks down a little at the end but if you promise to hang with me for the next
04:34two
04:34minutes I promise to try and walk the delicate line between trying to make things simple to
04:38understand without oversimplifying or being condescending fluidization is just when you
04:42have enough upward air so that the force of the air pushing on each grain of sand is equal to
04:47the
04:47downward force of gravity or weight and when that happens on any individual grain of sand it hovers
04:53in equilibrium like this you can think of forces acting on an object like a tug of war if an
04:58object
04:59is in equilibrium that means there's a tie and it doesn't accelerate in either direction just like
05:04in a real tug of war if the sides are even however if you add stone cold steve austin to
05:08this side that
05:09will make it totally unbalanced and will start to move this way which is actually what happens
05:13if you accidentally turn the air up too high as a fluidization occurs in that sweet spot where the
05:18sand particles hover in equilibrium which makes them easy to move around this is also the reason
05:23sometimes you'll see pools pumped with air to cushion the landing for the divers then you notice
05:27that some stuff floats in the sand and other stuff sinks this has to do with the buoyancy force
05:32which is a function of the density of the surrounding fluid and the volume of the object itself
05:38whenever an object exists in a pressure gradient there are forces from pressure pushing in on
05:42all sides but they push a little bit harder the deeper that you are which is why it hurts more
05:46to be the bottom guy in a dog pile or it hurts your ears more the deeper you dive in
05:51the pool and this
05:52makes sense because the deeper you dive the more water there is above you pushing down and if you add
05:56up
05:57the size and direction of all those arrows a bunch of stuff cancels out and you're left with one net
06:01force
06:01pointing upwards that is the buoyancy force and if your buoyancy force happens to be greater than your force
06:06from gravity you float and if your buoyancy force happens to be less than the force from gravity you
06:11sink now we usually think of buoyancy with water but you could think of things like helium balloons
06:16being buoyant in our atmosphere so here's a trick question which of these has a higher buoyancy force
06:22it's actually the rubber ball buoyancy force has nothing to do with the density of the object
06:28just the volume so since the rubber ball takes up more space it has a higher buoyancy force but you
06:34might object then why does the rubber ball sink and the balloon floats remember it's a tug of war
06:41the rubber ball sinks because the force from gravity on the thick rubber skin in the air inside is bigger
06:46than the buoyancy force but for the balloon even though it doesn't have as big of a buoyancy force
06:51compared to the ball it still floats up because that buoyancy force is bigger than the weight arrow
06:56from the helium and the thin rubber shell and the helium will keep rising like a ball floating up from
07:00deep
07:01in a lake and then it will eventually hang out where the density of the atmosphere is roughly equal
07:05to the density of the helium in the balloon because that's where the tug of war becomes equal
07:09we made it through now back to my nephews
07:39and everyone starts to move as soon as paja paja starts to move
07:49oh no no i can't get it out
07:52get it
08:05okay cut it
08:15oh
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