1.) The Heli-top is based on the principles of rotational momentum and lift.
2.) The child(ren) will interact with the Heli-top by putting the funnel-shaped tip in contact with the a smooth hard surface. To use the Heli-top in a way that permits flight, the child will have to spin it in a quick clock-wise manner.
3.) The cost to make a Heli-top will be relatively very low. Only a low strength plastic is necessary to withstand the forces put on the Heli-top during use. It will be very durable, because the most force placed on the top will be the forces of impact from the ground under its own weight after flight. It is also safe due to its size (not a choking hazard) and its lightweight composition.