Institute of Technologists demonstrated a "fluidized bed interface," with which sand behaves like liquid, at Computer Entertainment Developers Conference (CEDEC) 2017.
CEDEC 2017 is one of Japan's largest-scale conferences for developers. It took place from Aug 30 to Sept 1, 2017, in Yokohama, Japan.
Small holes are made in the bottom of a container of sand, and air is sent from underneath by using a fan. The size of the holes is smaller than the diameter of the sand particle. When the force provided by the fan becomes equal to the gravity force applied to the sand, the sand behaves like liquid.
When the fan is in operation and a human is standing on the sand (or a basketball is being strongly pressed to the sand), the person (or the ball) sinks into the sand. When I touched the sand, it felt like a fluffy bead cushion. When the fan is turned off, it returns to normal sand. When a basketball is buried in the sand and the fan is turned off, the ball keeps being buried in it.
With the interface, sand becomes like liquid when its particle is smaller than a certain level, said Yasushi Matoba, a part-time instructor of Institute of Technologists. However, when the particle of sand is too small, the sand is blown up by the fan. When the particle is too large, air easily passes through the sand, and the sand does not behave like liquid.
The fluidized bed technology is currently used for incinerators, etc and is not rare. However, Matoba said, "There has never been equipment that a human can enter (and uses a fluidized bed)." He started to manufacture the interface in 2016 and exhibit it in 2017.