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# The Uninflating Balloon by Tom Robinson

## Experiment Overview

This experiment explores the fact that air takes up space. You may not be able to see it, but it's there and this experiment will demonstrate that. The goal will be to blow up a balloon inside a plastic bottle. But in the first version of this experiment, you will first attempt to inflate the balloon without placing anything else inside the bottle. You will then add a straw to see if it has any effect on your ability to blow up the balloon. In the second version, the bottle will first be untouched and then will have a small hole placed in it. Your task will be to determine whether that hole has any effect on your ability to inflate the balloon.

## Science Concept

Air takes up space. You actually demonstrate this every time you take a breath. As you breathe in, your lungs expand to hold the air. When you breathe out that air, your chest and lungs deflate a little bit. In this case, you are dealing with air that already resides inside the bottle. When you try to put air into the balloon, it has to displace the air already in the bottle. With no exit path available—this happens in the first test when nothing is added to the bottle, and in the second when no hole is present in the bottle—the existing air stays right where it is and it becomes impossible for the balloon to inflate. However, by adding the straw, the air now has a path to travel and it can escape. This makes room for the new air you are breathing into the balloon and it easily inflates. With a hole in the bottom of the bottle, the air inside the bottle just escapes out the hole and this is what allows the balloon to inflate.

KIDS’ LAB LESSONS

## Materials

• 2 (20-ounce or 1-liter) plastic bottles

• Drinking straw

• Thumbtack

• Medium balloon

## Procedures

part I

1. Place the balloon inside the bottle with its mouth sticking out the top of the bottle.

2. Blow into the mouth of the balloon and try to inflate it. You should find it very difficult to do.

3. Now place the straw next to the balloon inside the bottle. Be sure that the end of the straw sticks out of the mouth of the bottle.

4. Try inflating the balloon again. You should find it much easier to do so.

part ii

1. As before, place the balloon inside the bottle with its mouth sticking out the top of the bottle.

2. Blow into the mouth of the balloon and try to inflate it. You should find it very difficult to do.

3. Using the thumbtack, poke a small hole, about the size of a nail hole, in the bottom of the bottle.

4. Now when you try to inflate the balloon by blowing into its mouth, it should inflate easily.

## Questions for the Scientist

1. Why did the balloon not inflate initially in either of the tests?

2. Where did the air you blew into the balloons go in both tests?

3. The straw and the hole you made in the bottle allowed air to escape from the bottle. Where did this air come from?

4. If you are blowing air into the balloon and air is escaping through the straw or hole, how does the balloon inflate?