When air is pumped through sand in just the right way, the sand begins to behave a lot like a fluid. As air escapes between the sand particles, items placed in the sand will begin to float. Others will sink. And when the air stops, the sand behaves more like a solid again. This is the fluidization of sand and it looks and feels really cool.
After creating 25 failed homemade versions of this experiment, former NASA JPL engineer Mark Rober succeeds in making a giant fluidized bed of sand inside an old hot tub. In the video above, he explains some of the science behind how this Liquid Sand Hot Tub works, and then he drops balls, bricks, and his nephews into it to see what might happen.Watch these related videos: An octopus that makes quicksand for a quick escape and Making Sand Swim.