You can try as hard as you want, but you’ll never be as cool an uncle as ex-NASA JPL engineer Mark Rober. Using elaborate experiments, he makes learning about science even more entertaining than Bill Nye did, and his latest invention is a sand-filled hot tub that somehow still behaves like water you can swim in.
As the air works its way up from pipes at the bottom of the hot tub, it makes its way in-between all the granules of sand, reducing the friction and causing the mixture to behave like water. Lighter objects will float atop the sand, while heavier and denser ones will sink right to the bottom. At least until the air supply is stopped, at which point the sand locks into place, trapping everything in it.