falling water/sand

Posted on beginners forum originally , but did not get any reply. Maybe it’s not a beginner question. So try my luck here.

New to OF and interactive art. Any one please gives me a hint how this is done?(falling water or falling sand interacting with body) Especially the interaction of the particle with the shadow? Need to use physical engines like Box2d for the particle? Or there is simple ways? Thanks.

http://www.youtube.com/watch?v=8YXvm9ZIiHU&feature=player-embedded