00:00I'm sitting in a hot tub filled to the brim with solid sand.
00:09This is one of the coolest things ever. If you take a tub of sand like this
00:13and then add air in just the right way, it basically becomes a liquefied soup.
00:47In science, this is known as a fluidized bed. It's used in industrial applications such as
00:52powder coat painting or in grain silos to make sure that the grain flows 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.
01:37So today I'm going to show you how to make a simple version like this yourself. And then
01:41because I became curious what it would feel like to be fully immersed in something like this,
01:45we made a hot tub sized version. As you can see from the 60 year old video from the Royal
01:49Institute of Science, this demo isn't exactly new. I'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. So I started combing
01:59through a bunch of patent drawings for massive industrial sized fluid beds. And I noticed that
02:03instead of one big inlet, they all had a bunch of small holes to deliver the air. So starting with
02:09that 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. But
02:19the key
02:19is to drill two one millimeter holes, 90 degrees apart from each other, and then do a bunch of
02:25those spaced 25 millimeters apart. Then you glue all the pipes together and just make sure you orient
02:30the holes down so that will keep the sand from getting in. And then you just seal off the container
02:34with some hot glue and then fill your container with either fine sand or we found glass beads worked
02:38really well. And you can power with a small air compressor like this, or you could just rent
02:41a large nitrogen container like this for about 30 bucks. And that'll give you 10 minutes of runtime.
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.
03:18Ohhhh!
03:46Now that it was tested and ready, in my ongoing quest
03:49to be the favorite uncle, I decided to surprise my nephews with it.
04:12But before we get to swimming in sand, let's talk about the science behind a fluidized
04:17bed.
04:18And when we don't, click away if you think science is boring.
04:20If you're new here, you should know that my approach to science is similar to velociraptor
04:24hunting 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, I mean the analogy breaks down a little at the end, but if you promise
04:33to hang with me for the next two minutes, I promise to try and walk the delicate line between
04:37trying to make things simple to understand without oversimplifying or being condescending.
04:41Fluidization is just when you have enough upward air so that the force of the air pushing on
04:46each grain of sand is equal to the downward force of gravity or weight.
04:49And when that happens on any individual grain of sand, it hovers in equilibrium like this.
04:55You can think of forces acting on an object like a tug of war.
04:58And if an object is in equilibrium, that means there's a tie and it doesn't accelerate in
05:02either direction, just like in a real tug of war if the sides are even.
05:05However, if you add Stone Cold Steve Austin to this side, that will make it totally unbalanced
05:10and will start to move this way, which is actually what happens if you accidentally turn the air
05:14up 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.
05:22This is also the reason sometimes you'll see pools pumped with air to cushion the landing
05:26for the divers.
05:27Now 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
05:34fluid 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
05:46more to be the bottom guy in a dog pile or it hurts your ears more the deeper you dive
05:51in the pool.
05:51And this makes sense because the deeper you dive, the more water there is above you pushing
05:55down.
05:56And if you add up the size and direction of all those arrows, a bunch of stuff cancels out
05:59and you're left with one net force pointing upwards.
06:02That is the buoyancy force.
06:04And if your buoyancy force happens to be greater than your force from gravity, you float.
06:07And if your buoyancy force happens to be less than the force from gravity, you sink.
06:12Now we usually think of buoyancy with water, but you can think of things like helium balloons
06:15being buoyant in our atmosphere.
06:18So here's a trick question.
06:19Which of these has a higher buoyancy force?
06:22It's actually the 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.
06:34But you might object.
06:35Then why does the rubber ball sink and the balloon floats?
06:39Remember, it's a tug of war.
06:41The rubber ball sinks because the force from gravity on the thick rubber skin and the air
06:45inside is bigger than the buoyancy force.
06:48But for the balloon, even though it doesn't have as big of a buoyancy force compared to
06:51the ball, it still floats up because that buoyancy force is bigger than the weight arrow from
06:56the helium and the thin rubber 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
07:05to the density of the helium in the balloon.
07:07Because that's where the tug of war becomes equal.
07:09We made it through.
07:10Now back to my nephews.
07:11We made it through.
07:13We made it through.
07:39Everybody starts to move as soon as Panya Panya starts to play.
07:50Oh no, I can't get it up.
07:52Get it.
07:53Got it.
08:13Okay, cut it.
08:17Back up.
08:51Okay, cut it.
09:05Okay, cut it.
09:08All right.
09:09Okay, try it.
09:13All right.
09:13You can see it.
09:15Okay.
09:16Okay.
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