Ever wonder how meteorologists figure out what weather is coming? They look at things like temperature, wind direction, and barometric pressure (the weight of the air). Explore some of the changes in the spring air for yourself with a homemade barometer.

Materials

• Scissors
• 12-inch balloon
• Widemouthed jar (such as a large mayonnaise jar)
• Wide rubber band
• Clear tape

• Needle or straight pin
• Plastic straw
• Tacky glue
• Cardboard or poster board
• Pencil or pen

Instructions

1. Cut the neck off the balloon and discard it. Stretch the balloon over the mouth of the jar and secure it with the rubber band.

2. Tape the needle or pin, point facing out, to the end of the straw. Use a generous pool of glue to attach the other end of the straw to the center of the balloon.

3. Prop the cardboard against a wall with a fairly constant temperature and set the jar just in front of it, but not touching. Label "high" and "low" as shown. Mark the spot at which the needle now points. Check the barometer every few hours and mark the changes on the board.

4. Why it works: As weather patterns shift, the air pressure around the jar changes, while the pressure inside it remains the same. As the pressure outside increases, the balloon is pushed down, forcing the needle up. As the pressure outside falls, the balloon swells, sending the needle down.

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