The Plane Entity is just a simple Entity with a Shape attached to it.
The Spawn Pile doesn't have any Physics component attached to it, but its Entity Graph will spawn a new Box every Three seconds and Push it down towards the Ground.
The Ball Thrower doesn't have any Physics component either, but it will spawn a new ball in the viewing direction if the spacebar is pressed. The Logic is pretty similar to the one of the Spawn Pile: Spawn a new entity and use the Physx Push Node to push it in a specific direction, in this case the camera viewing direction.
That's it for the Contacts scene, it's a pretty simple one.
You will notice that the Boxes only collide with the blue spheres and the Ground plane: as an exercise try to make it so that the boxes also collides with each other.