Air Pressure - Magic Balloon (Rana Khan)
Author
Rana Khan
Principle(s) Illustrated
This demonstration shows the fundamental physics of air pressure.
Questioning Script
Materials
1.) helium balloon (2)
2.) 1.5 -2 liter plastic bottle (2)
3.) pin or tack
Procedure
1.) Make a small hole at the bottom or side on one of the plastic bottles.
2.) Place one balloon inside the neck of each bottle and stretch the opening of the balloon over the top of the
bottle, so that the opening is covered completely.
3.) Have two volunteers blow inside each bottle. Observe what happens.
Prior knowledge & experience:
Students are already familiar with the properties of a balloon and how to blow it up.
Root question:
1.) When I blow into the bottle with the balloon what will happen?
2.) Why does one balloon expand inside the bottle and the other balloon does not
expand?
3.) Explain why the bottle with the hole at the bottom allows for the balloon to expand.
4.) What have you learned about air pressure from this activity?
5.) Why does the balloon inflate when you pinch the base out?
6.) Name a part of your body that acts the same way as these two demonstrations.
Target response: Students will learn that when there is an opening in an enclosed area such as a bottle or a cup; air can escape and allow room for something else (like the inflated balloon). This example of air pressure relates to our lungs. As we breathe air in, our lungs shrink; and as we breathe out our lungs expand. This is the same principle when your ear pops.
Common Misconceptions:
When blowing up a balloon, we move air into a compressed space, as the balloon inflates. When the balloon is placed inside a sealed bottle, there is no way for the bottle's air to escape, so the balloon does not inflate. The pressure inside the bottle is greater than the pressure that occurs from blowing on the balloon. When there is a hole at the bottom of the bottle, the air can escape; hence the balloon inflates.
Photographs:
Video and Alternative Method to blow a balloon without blowing in it.
The alternative method to show the effect of air pressure is as follows.
Material:
One plastic bottle.
One balloon.
A scissor.
Question.
1- Can I expand the balloon without blowing in the balloon as we saw in our previous experiment?
2- If yes, how and why?
3- If not, why not?
Experiment:
Take the plastic bottle and make a hole in it a little below the half way. Place the balloon on the mouth of the bottle by fitting it on it as seen in the above photo. Rather than blowing on the top of the bottle into the balloon, suck the air out of the bottle through the whole in the bottle. You will see the balloon expanding inside the bottle.
4- What happened? Explain.
Explanation:
There is air inside the bottle and outside the bottle. By sucking out the air from the inside of the bottle, we are producing the air difference, means lower air pressure inside the bottle and the outer air pressure is now more and the air pushes inside the balloon to the lower pressure thus expanding the balloon.
Video
Additional Resources/References
Balloon Air Pressure Magic (Instructions)
How does air pressure work? (Content information)