Loony Balloons


Contributed By: Explora
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Experiment Category: 


Discover geometry by creating shapes from loops of paper.

What You Need: 

  • Two Balloons
  • Water

To Do and Observe: 

1. Pour a little bit of water into one of the balloons and tie the neck. 

2. Squeeze and push the small water-filled balloon into the empty balloon. 

3. Blow into the outside balloon and tie the neck so that the little water-filled balloon is inside the outer inflated balloon. 

4. Toss the balloon to someone else, or throw the balloon up in the air and catch it. What happens?

What's Going On: 

The balloon wobbles as the water-filled balloon rolls around inside. An inflated balloon has little mass compared to the water-filled balloon inside it. When the water-filled balloon inside the inflated balloon is put into motion, the inertia (the tendency to keep moving in the same direction) of the water-filled balloon overpowers the balloon’s motion and causes eccentric behavior. The eccentric behavior of the balloon can also be linked to the changing center of gravity of the balloon. The center of gravity is the average location of the weight of an object. As the inner balloon moves, so does the average weight, which causes the balloons to loop. 

The balloon moves oddly to the viewer who cannot see the motion of the inner water-filled balloon. Gravity also pulls the water-filled balloon, which causes it to travel downward at an unexpected speed. When the water-filled balloon and the inflated balloon move, they act as a system.

Parent/Teacher Tips: 

NOTE: If the water-filled balloon is too difficult for the students to put into the outer balloon, try using a small lump of clay (about the size of a ping pong ball). 

After the students have observed what the loony balloon does they can further this experiment by trying to answer the following questions: 

add bullets Does it matter how much water is in the inner balloon? 

How does a bouncy ball or large marble affect the center of gravity of a flying balloon? 

Are there any objects placed in the inner balloon the will not affect the center of gravity of the outer balloon?