Weather Station

Make Your Own Barometer

What it does

This experiment lets you create a simple barometer to measure air pressure. For best results, read the directions before you start the experiment!

What you need

A small jar, like a baby-food jar
A wide-mouthed, 1-quart jar
2 balloons
2 rubber bands
A flat toothpick
Scissors
Glue

What to do

Cut the top off of one of the balloons (the end with the hole).
Stretch the remaining part of the balloon over the top of the small jar, using a rubber band to hold it in place.
Glue the large end of the toothpick to the rubber cover so that it extends off of the jar. Allow the glue to dry.
Carefully place the small jar inside the big jar.
Cut the bottom off of the remaining balloon.
Stretch the remaining part of the balloon (with the hole) over the top of the large jar, using a rubber band to hold it in place.
Tie off the neck of the balloon so that the hole is closed.
Using the neck of the balloon, pull up and push down on the balloon to change the air pressure in the big jar.
Watch what happens to the toothpick.

What it's all about

As you move the balloon over the big jar, the toothpick moves up and down. When you push down on the balloon, the air pressure in the jar increases and pushes the lid of the small jar down. This makes the toothpick point upward.

When you pull up on the balloon, the air pressure in the big jar decreases because the air has more room to spread out. This causes the lid on the small jar to expand and push the toothpick down.

Remember, be sure you have a parent, teacher, or other adult help you!