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Blow Hard - A Science Experiment

How do you explain that something you canít see, canít usually feel or taste, takes up space? Hereís a super simple, super fun science experiment to do just that.


7 inch balloon
a glass soda bottle (6 ounce or 10 ounce size)
drinking straw
ball of clay (about walnut size)
masking tape


1. Use the scissors to cut the lip (the rolled part at the opening) off of the balloon.

2. Pull the balloon over the straw until it covers one half inch of the straw.

3. Wrap tape around the edge of the balloon so it is attached to the straw and no air can leak out around the edges of where it is cut.

4. Place the straw and balloon inside the soda bottle so that the balloon almost touches the bottom of the bottle.

5. Press the clay around the straw and the mouth of the bottle to make the bottle airtight, except where the straw sticks out. Make sure to leave enough straw outside the bottle to be able to blow into it.

6. Blow into the straw. Can you inflate the balloon?

What happens? You can only inflate the balloon a tiny bit no matter how much or how hard you blow.

Why? When you put the balloon in the bottle, the bottle is not really empty. It is filled with air. If you blow the balloon up, it will get bigger. To make room for the balloon, you need to get rid of some of the air in the bottle. But, but there is no way for the air to leave the bottle because you have it plugged up with the clay.


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