Apps like this seem simple on the surface, but it really takes some thought to try and make art from a physics based app. Unlike traditional art styles and forms where we tend to stay between the lines or on the canvas this app is like trying to make a simple painting while floating in space. It feels like it can just float wherever and go beyond the canvas and I believe that is where the challenge lies with this type of app.
But thats what i like about it. Its good to find something like this to free you from the traditional art forms that we spend years attempting to master. Try making art like this in the traditional way and youll see how hard it really is!
Ase o/m/g about Flowpaper: Drawing & Animation