A barometer measures atmospheric pressure, which is the weight of the air column above a specific point. Changes in this pressure signal shifts in weather patterns, making the barometer a useful tool for basic forecasting. This article provides instructions for constructing a simple, functional barometer using readily available household items, allowing you to observe these atmospheric changes firsthand. The device relies on a flexible membrane to register pressure fluctuations.
Required Materials and Preparation
The construction of this simple barometer requires a few common items: a wide-mouthed glass jar, a balloon or a piece of flexible plastic wrap, a large rubber band, a clear drinking straw, tape or strong glue, scissors, and a stiff piece of index card or cardstock. The jar will serve as the sealed chamber, while the balloon or plastic wrap acts as the pressure-sensitive membrane.
Preparation involves cutting the neck off the balloon to create a flat, circular membrane large enough to stretch tightly over the jar’s opening. Use scissors to cut one end of the drinking straw into a sharp, visible point. This sharpened end will track the pressure changes against the backing scale.
Step-by-Step Assembly
Begin the assembly by firmly stretching the cut section of the balloon across the mouth of the glass jar, pulling it taut. Secure the membrane with a large rubber band wrapped around the rim of the jar to create an airtight seal. This seal is necessary to trap the air inside at a constant initial pressure.
Next, attach the straw pointer to the center of the stretched membrane. Use a small piece of tape or a dab of strong glue to secure the unpointed end of the straw directly onto the middle of the balloon surface. The straw should extend horizontally past the edge of the jar, acting as a lever arm to amplify the membrane’s subtle movements.
Finally, set up the backing scale by taping the index card vertically behind the pointed end of the straw. Position the card so the straw’s tip points toward it without actually touching it. This scale will be used to mark and track the pointer’s movement over time.
The Science Behind the Measurement
The homemade device functions based on the principle of differential pressure between the sealed air inside the jar and the atmosphere outside. When the balloon membrane is stretched and secured, it traps a specific volume of air inside the jar at the current atmospheric pressure. This trapped air remains at a constant pressure because it cannot escape, creating a fixed reference point.
Atmospheric pressure constantly pushes down on the exterior of the balloon membrane. If the external atmospheric pressure rises, it exerts a greater force on the membrane than the air pressure trapped inside the jar. This increased force pushes the flexible membrane slightly inward, causing the attached straw pointer to pivot and move upward against the scale.
Conversely, if the external atmospheric pressure decreases, the constant pressure of the air trapped inside the jar becomes greater than the pressure outside. The air inside pushes the membrane slightly outward, causing the straw pointer to pivot downward. This simple lever system translates minute vertical movements of the membrane into noticeable changes in the pointer’s position.
Reading and Interpreting Pressure Changes
To use the finished barometer, place it in a stable location away from direct sunlight or sources of temperature fluctuations. Mark the initial position of the straw’s point on the index card with a horizontal line and record the date and time; this serves as your baseline reading.
Over time, observe the straw’s movement, marking the new position on the card at least once or twice a day at the same time. The direction of the pointer’s movement provides a simple indication of impending weather changes. A consistent upward movement of the straw indicates rising atmospheric pressure.
Rising pressure is associated with the descent of air masses, which suppresses the formation of clouds and typically leads to clearer, fairer weather conditions. Conversely, a sustained downward movement of the straw signifies falling pressure. Decreasing pressure often accompanies rising, moist air, which condenses to form clouds, signaling the increased likelihood of stormy or wet weather.