# Make a Barometer

Let's make our own barometers!

A barometer is a tool used for measuring atmospheric pressure, which can be used to help forecast weather. Atmospheric pressure is the amount of force the air places on objects.

##### What you’ll need:
• 1 Jar
• 1 balloon
• 1 Rubber band
• 1 straw
• Tape
##### Instructions for making the barometer
1. Cut the neck of the balloon off. This does not need to be particularly precise
2. Stretch the balloon over the jar so that the balloon is flat across the opening. Secure the balloon to the jar.
3. Cut the straw on a diagonal to get a pointed end. If the straw has a bendy portion, cut that off.
4. Attach the straw to the balloon using tape. Make sure the end of the straw is near the center of the balloon.
##### How to use the barometer
• Place the barometer in front of a piece of cardboard or paper, with the end of the straw pointing to the paper/cardboard. Draw a line where the straw points to.
• Above the line indicates high pressure. High atmospheric pressure usually occurs during fair weather.
• Below the line indicates low pressure. Low atmospheric pressure usually occurs during cloudy, rainy weather.
##### How does it work?

When you make the barometer, the pressure inside and outside the jar are approximately the same. But, as you let it sit, changes in atmospheric pressure will only affect outside the jar. So, when atmospheric pressure increases outside the jar (which happens with high pressure conditions), it pushes the balloon into the jar a bit. This will lower the end of the straw attached to the balloon in the middle, which tilts the straw up!

And, when the atmospheric pressure lowers, there is less pressure on the balloon from the outside and more pressure inside the jar. This pushes the balloon slightly out of the jar. This tilts the straw down!