Dry sand can bubble and swirl like a fluid
A jiggle and flowing gas make solid particles of different densities move as if water or oil
![solid grains in a glass chamber](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2019/04/042619_cg_sand-liquifies_feat.jpg?fit=860%2C460&ssl=1)
BUBBLING UP Gas flowing up through a gently vibrating glass chamber can cause solid grains to simulate a well-known fluid behavior. Here, bubbles of less dense sand (blue) rise through a layer of denser sand (white).
Alex Penn/ETH Zurich