When air gets passed through sand, it behaves like a liquid

I watched this video, it was really cool, It is difficult to build a set up for this though

It has to be pretty fine sand though. The larger grains wouldn't do as well.

It's not that it behaves like liquid, it that liquid is a fluid and moving air acts as a fluid. Bernoulli's principle is why the balls float.

Mmmmm, airborne silica