How to simulate falling small pieces of paper to the ground? It's like when someone wins a prize at a party on TV. Small colored pieces of paper fall from the ceiling. That's what I'm trying to simulate. I managed to do everything using a particle system except the final part of physics. When the particles (planes) touch the ground (a scaled cube), they don't go back to their horizontal position. Their final positions give the feeling as if they are darted to the ground. 



How to make them adjust their rotation to the horizontal position when they touch or collide with the ground?

Thank you,
If you want the pieces to collide with the floor, convert particles to mesh and apply rigid body. Make the floor passive rigid body and the pieces active one.