How to Build a Barometer

A barometer is an instrument used to measure atmospheric pressure. Although most weather forecasters use the most formal, and perhaps expensive, barometers they can find, their underlying principles are rather simple. A simple barometer can be constructed out of the cheapest of household objects.

Instructions

Difficulty: Easy

Things You’ll Need:

• Clear glass or plastic jar
• Drinking straw
• Tape
• Modeling clay
• Food coloring

1. Fill the jar with cold water until it is less than half full. Add a few drops of food coloring to see the water more easily.
2. Place the straw into the jar and tape it to the inside. The bottom end of the straw should rest in the water but not touch the bottom of the jar.
3. With your mouth, suck the water halfway up the straw. Pinch the drinking end to trap the water. Take your mouth off the straw.
4. Block the drinking end of the straw with modeling clay or tape.
5. Attach a piece of paper on the outside of the jar.
6. Leave the jar somewhere it's neither too drafty nor too sunny.
7. With a pencil or pen, mark and date the level of the water in the straw each day. Increasing atmospheric pressure will force the water in the jar downwards (and the water in the straw upwards), and vice versa. Rising pressure usually indicates dry and gentle weather, whereas falling pressure can often indicate a coming storm.

Tips & Warnings

• Remember that, especially with homemade barometers, there are few hard-and-fast rules for weather prediction.