Age range: 7–13
Time: 30 minutes setup + 2–3 days observation
Concepts: air pressure, weather, fluids
Goal
Build a simple barometer to see pressure rise and fall with changing weather.
Materials
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Glass jar (wide mouth)
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Balloon or plastic wrap
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Rubber band
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Tape
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Drinking straw
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Index card or paper for scale
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Marker
Safety
Use glass carefully; adults should cut balloon tops if needed.
Steps
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Make diaphragm: Cut the neck off a balloon. Stretch the balloon over the jar mouth; secure with a rubber band. The surface should be taut.
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Pointer: Tape a straw flat on top so one end sticks out over the jar’s edge like a pointer.
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Scale: Place an index card behind the straw tip. Make a baseline mark.
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Calibrate: Over several hours, note straw position. Mark “higher” and “lower” positions as weather changes.
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Record: Check 2–3 times per day for a week. Log direction and any observed weather (sunny, cloudy, rainy).
What’s Happening
When outside air pressure rises, it pushes the diaphragm down, lifting the straw tip; falling pressure lets the diaphragm bow up, lowering the tip.
Troubleshooting
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Straw not moving? The balloon may be loose; retighten.
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Temperature swings indoors can also move the pointer—keep the jar away from vents.
Extensions
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Compare readings to a local weather app’s barometer.
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Make two barometers in different rooms; test indoor pressure changes when doors/windows open.
