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i'm sitting in a hot tub filled to the brim with solid sand. (laughter) 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 soup. (music) 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. with air on the top surface is nearly frictionless. it's like an air hockey table. (music continues)

and then when you cut off the air, it freezes everything exactly where it's at. 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 sized version. as you can see from the sixty-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 sized 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 1 millimeter holes 90 degrees apart from each other and then do a bunch of those spaced to 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 can 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 ten minutes of run time. as usual, i will put a link to all of the parts i used the build in the video description. so my buddy ken can had an old broken spa on 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. (laughter) ahhh! now that it was tested and ready, in my ongoing quest to be the favorite uncle...

pew pew pew pew, ahhh!, (screaming) i decided to surprise my nephews with it. (fizzing noise) woah, woah! ahhhhhhhhh! (music) (laughter and screaming) but before we get to swimming in sand, let's talk about the science behind a fluidized bed. wait wait, 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... rawr... clever girl, velociraptor shrieks 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 a fluidization occurs in that sweet spot where the sand particles hover in 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 buoyancy 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 can 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. phew! we made it through! now back to my nephews. (giggling) (screaming) (screaming and laugher) aw! no, oh no! i can't get it out!

get it! (nephew): i can't! (other nephew): got it! turn it off! ok, cut it! ah! (laughter) christmas is coming, and with the help of casper who happened to support this video, i got your back. and with the exception of a bob ross chia pet, what could possibly be better than the gift of a good night's rest? with casper, you order online, and then they'll ship it right to your door for free and it shows up in a box like this, and then you open it and it magically expands to actual mattress size! we totally love ours, and with over 20,000 reviews with an average rating of 4.8 stars on sites like amazon, there's a pretty good chance you'll love it, too. and they're also affordable because you cut out the sweaty price haggling commission based middleman who works at a typical mattress store.

and you could try it out for a hundred days, and if at the end of that you're like meh... they'll come pick it up for free, you get all your money back, no questions asked. so, skip the crowded mall this year and finish your christmas shopping right now by going to casper.com/markrober and using promo code mark rover for $50 off any mattress. merry christmas! and thanks for watching. (epic outro music)

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