How to Build a Simple Barometer

A barometer measures the change in atmospheric pressure, usually as a means to predict ensuing changes in the weather. Liquid barometers use the movement of mercury or water through a tube to measure the change in pressure. Aneroid barometers, on the other hand, measure the expansion and contraction of a flexible metal cell with the change in air pressure. Commercially produced barometers tend to be sturdy, complicated instruments, but you can construct a simple aneroid barometer at home with a balloon stretched over the mouth of a jar.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• Drinking straw
• Wide-mouthed glass jar
• Round balloon
• Rubber band
• Scissors
• Glue
• Large sheet of paper
• Tape

1. Cut the balloon off at the widest point. You will use the top and can discard the bottom part with the hole.

2. Stretch the top of the balloon tightly across the opening of the jar, like a drum, and secure it with the rubber band. The seal must be airtight.

3. Glue one end of the straw to the center of the stretched balloon. The other end of the straw should extend over the side of the jar.

4. Allow the glue to dry. The length of time will vary depending on the type of glue, so refer to the glue's directions.

5. Tape a piece of paper to a wall and set the jar next to it so the straw is parallel to the paper. However, be sure that the straw is not touching the paper.

6. Draw a mark on the paper to indicate where the straw is pointing. You can also add the date and time that you recorded the mark.

Tips & Warnings

• Check the position of the straw to indicate changes in atmospheric pressure. If it rises above the previous day's point, the pressure is rising, and if it points below the mark, then the pressure is falling.
• Keep the seal airtight or the changing pressure will force air into or out of the jar instead of stretching the balloon.

Resources

• The Aneroid Barometer and How to Use It