The Ruiz Brothers over at Adafruit have created a really lovely sand simulator using a Raspberry Pi Zero, an accelerometer, an RGB LED matrix display, some small items and 3D-printed parts. Philip Burgess wrote the code which “simulates physics by calculating collisions and terminal velocity”. The 3D-printed handles border the LED display and two buttons switch mode and reset the simulation. You can read a tutorial here which explains how to make your own and see a video of it in action below: