Science & Technology

Watch People Swim in This Bubbling "Liquid" Sand Pool

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Quicksand might not be the pop-culture phenomenon it was decades ago, but the idea of sinking into a pit of liquid sand is still just as captivating. That's why we can't look away from this video from Nickipedia: a human-sized pool of bubbling, churning, liquidized sand. Check it out below, and keep reading for the scientific explanation.

Just a Phase

As Nick Uhas explains in the video, what they've created is known as a "fluidized bed." That's a mixture of two different phases of matter: solid (sand, in this case) and fluid (air). It's not just good for backyard antics, either. All sorts of industries use it, from the oil and gas industry to food production. If you've ever seen metal painted with an opaque matte coating, you've seen the effects of fluidization — this "powder coating" uses the same technique as Uhas's sand pool, just with paint particles swapped in for grains of sand.

So how does it work? Fluidization happens when you have just enough air pushing upward to counteract the downward force of gravity on each particle of sand. That puts it in a state of equilibrium, allowing the sand to float freely as if it's in a liquid state. Mark Rober, former NASA engineer and the inspiration for Uhas's project, explains it this way: "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."

But when one team recruits a big burly wrestler to play, it sends everyone in one direction. That's what happens when you don't use exactly the right amount of air — sand goes everywhere. It's really important to get the pressure just right.

As a result, Uhas and his team had quite a project on their hands. "This was certainly the biggest build the Nickipedia channel has ever taken on," he says in the video. "It was three weeks of blueprinting, digging, drilling, cutting, soldering, and a ton of problem solving." But once it was complete, Uhas turned on the nitrogen tanks, dove into the bubbling, churning pool, and floated.

The Internet Strikes Again

Liquid sand pools are nothing new. As far back as 1959, British physicist Lawrence Bragg performed demonstrations at the Royal Institution where he fluidized a dish of sand and showed how heavy metal balls floated in the newly liquid medium. It's a handy science demonstration because it makes it easy to visualize how a solid melts to become a liquid. When a substance is frozen, the molecules are densely packed together, sort of like sand in a sandbox. As it melts, the molecules break away from each other and move freely, just like when the pressurized air "frees" the sand to act as a liquid.

The modern liquid-sand craze seems to have taken off a few months ago, when a GIF of the phenomenon made the rounds on Reddit. YouTubers quickly took up the challenge, building and posting videos of their own fluidized beds. However, to our knowledge, the The Nickipedia liquid sand pool is the only one that involves a boogie board.

Written by Ashley Hamer March 29, 2018