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Make Your Own Barometer
By John Cowens

Everyday materials are all you need to turn your students into a classroom full of weather forecasters

Every spring my enthusiastic sixth graders design, build and launch model rockets. As a prerequisite, students are required to understand basic concepts of meteorology. Basic weather instruments are easy to construct, as you'll see in these plans for a balloon barometer. A barometer measures air pressure. High air pressure usually means sunny, dry weather, whereas low air pressure indicates cloudy skies and precipitation.

wide mouth jars with balloons over them and a rain chart

High air pressure makes the balloon bulge (above), tipping the pointer to the sunny side. Low air pressure makes the balloon deflate (left), indicating that rain is on the way.

Balloon barometer
Materials:

  • large balloon

  • one quart-size jar with a wide mouth

  • thin straw or uncooked spaghetti noodle

  • strong rubber band

  • light-colored construction paper 9" x 12" (22.5 cm x 30 cm)

  • markers

Procedures:

  1. Cut the stem off the balloon.

  2. Stretch the balloon tightly over the mouth of the jar.

  3. Wrap the rubber band around the jar to keep the balloon from slipping.

  4. Tape one end of a thin straw (or a piece of uncooked spaghetti) to the center of the balloon.

  5. Fold the sheet of construction paper into thirds to make a triangular column.

  6. Stand the column next to (but not touching), the tip of the straw. Make a mark on the column where the tip of the straw is pointing.

  7. Check the barometer every three or four hours. If the straw's tilt changes, mark the new place on the column. In a journal, note what the weather was like on each day.

  8. Create and place a symbol on the triangular column for a sunny, dry day, a symbol for cloudy days and a symbol for precipitation: rain, hail, sleet and snow. Each time the tip points to a new place, make a mark and note the weather. After a few days, a pattern will emerge. You'll notice that when the straw moves up the column, a certain kind of weather follows. When the straw moves down the column, a different kind of weather follows.

How a balloon barometer works
Since the air inside the jar is held by the balloon, no air can escape and no extra air can enter. The air molecules are constantly pressing against all sides of the jar. Of course, air also surrounds and presses on the outside surface of the jar. When the pressure inside the jar is less than the pressure outside of the jar, the balloon sinks and causes the straw to rise. When pressure on the inside of the jar is greater than the outside pressure, the balloon will bulge, causing the straw to tilt downward. High pressure is associated with sunny and dry weather (the straw tilts upward). Low pressure is associated with dark cloud cover and precipitation (the straw tilts downward).

Websites

For an additional activity with directions for building a nephoscope click here. PDF 86KB

John Cowens teaches sixth grade at Fleming Middle School in Grants Pass, OR.

November/December, 2003, Vol.34, No.3