Here is another cool physics toy you can build to simulate the movements of grains of sand. The Animated LED Sand toy is pretty straightforward to build. You are going to need a Feather M0 Basic Proto, 15 x 7 CharliePlex LED Matrix, LIS3DH Triple-Axis accelerometer, and a few other small parts to get started.
As you move the device, the LEDs activate to simulate grains of sand as if they are affected by gravity. The code is written by Philip Burgess.