Paper in Bottle Challenge

Ask students what they think is happening. Some student-generated suggestions might include:

• The breath of air goes into the bottle, bounces off the back of the bottle and returns to the neck, pushing the paper out of the bottle.
• The breath of air is hitting the bottle and causing the paper to fall out.

What experiments can students do to test their claims? 

ex: Can students speculate why the paper ball doesn't follow the air stream that bounces off the back of the bottle?
ex: Can students use a blank sheet of paper with a small hole for the bottle opening to block the air from hitting the side of the bottle? 

Is it possible there is another explanation? How can we find out?

Is the bottle empty? Sure, it is empty of crumpled paper balls, but the bottle is not completely empty. There is air in the bottle, even before students blow a breath through the opening. What happens to that air when students attempt to force more air in the bottle? Air can be compressed, but that requires pressure, and our breath does not exert much of a pressure change in the bottle.

Some air from the student's breath gets into the bottle between the crumpled paper. What does this air do to the air that is already in the bottle, and in what direction is the air in the bottle going when additional air enters? That existing air will exit, and it will take the crumpled paper ball with it on the way out!