Physics toys are quite a lot of fun to play with. Adafruit has shared a guide that shows you how to build your own LED Matrix Sand Toy. This toy has LEDs that react to motion and act as if they are affected by gravity. The handles are 3D printed.
You are going to need a 64x 64LED Matrix, Adafruit RGB Matrix Bonnet for Raspberry Pi, and a few other simple components to pull this off.