The zoom ball shows how forces of push and pull can work together. When Partner #1 pulls the cords outward on one end, the Zoom Ball goes flying to the other side, as long as, Partner #2 pushes their ends together. The pushing action of the cords against the opening of the bottle sets it in motion. After the Zoom Ball reaches Partner 2, he sends it back by pulling on the cords while Partner 1 pushes on their cords. If both partners pull the Zoom Ball will go to the middle and stay. It takes opposite forces working together to make the Zoom Ball work!
If you want to make one for your class here's how: