A barometer is an instrument that measures air pressure. You can use a barometer to forecast weather, especially if you combine measurements with temperature and wind speed readings. Here are two easy ways to make a homemade barometer using simple materials. Also, what different readings mean so you can make your own weather predictions.
Make a Barometer with a Bottle and Glass of Water
All you need for this homemade barometer is a glass of water and a bottle that fits inside the glass. Ideally, select a bottle with a straight, narrow neck. The project works with other bottles, but you’ll have an easier time taking measurements with a long-necked bottle.
- Glass or jar of water
- Empty bottle that fits inside the glass
- First, turn the bottle upside down and make sure it fits inside the glass.
- Mark the neck of the bottle so you can take measurements. Use a permanent marker, a wax crayon, or tape. Using lines with numbers is a good idea. The numbers don’t really mean anything, but they make it easier to see if the water level is going up and down.
- Place the inverted bottle inside the glass so it stands straight. Pour water into the glass so it covers the bottle opening, plus a bit more. If you like, tint the water with food coloring.
- Tilt the bottle so a bit of the air inside escapes as bubbles.
How to Use the Homemade Water Barometer
- Temperature affects air pressure and water density, so keep the barometer in a sheltered location so sunlight or the air conditioner/heater won’t warm and cool it.
- Each day, record the measurement. This is the line the water inside the bottle reaches.
- If the water reaches the same mark the next day, pressure is remaining constant. This indicates the air is stable and no significant weather change is likely.
- If the water reaches a lower mark, it means the air pressure inside the bottle is higher than the air pressure outside. In other words, atmospheric pressure is falling. This indicates an upcoming weather change. If outside pressure drops a lot very quickly, it’s likely there’s an approaching storm.
- If the water inside the glass reaches a higher mark than the previous day, the air pressure inside the bottle is lower than the outside pressure. Atmospheric pressure is rising. Expect improving weather.
Limitations: A water barometer is highly effective. However, water does evaporate from this particular version, which can add error to your measurements, especially if you live in a dry environment. Another limitation is that it’s hard relating the measurements to actual air pressure values in units like millibars or Pascals. But, the numbers are not a big deal. What matters most is whether air pressure is rising, falling, or holding steady!
Make a Barometer With a Jar and a Balloon
The type of homemade barometer you make using a jar and a balloon is an aneroid barometer. Basically, an aneroid barometer is any non-liquid barometer. The premise here is that the container of air expands or contracts in response to atmospheric pressure. A homemade pointer taped or glued onto the flexible covering measures the air pressure difference.
- Large glass jar (or a sturdy plastic or metal jar)
- Plastic wrap or a large latex balloon, cut open to make a flat piece
- Straw or wooden skewer
- Rubber band
- Lined paper or index card
- Cover the top of the jar with the plastic wrap or latex and seal it onto the jar using a rubber band. The goal is making a smooth, flat surface. Make sure there is a good seal between the plastic and the jar rim.
- Lay the straw or skewer on top of the wrapped jar with the end on the middle of the covering. Tape or glue it in place.
- Place the lined index card or paper so you the straw or skewer points toward a line. As pressure changes, it points to a different line. Your goal is tracking movement up or down.
How to Use and Read a Homemade Aneroid Barometer
- Keep the barometer in a place with a stable temperature.
- Each day, record the level of the “pointer”.
- If the line does not change then the pressure inside and outside the jar is the same. When pressure does not change, no significant changes in weather are likely.
- If the pointer starts to drop it means the plastic lid is bulging up. Pressure inside the jar is greater than atmospheric pressure. Atmospheric pressure drops as weather conditions change. A large, fast drop indicates an approaching storm. Expect wind and precipitation in the form of rain or snow.
- If the point starts rising, the plastic lid is sinking down. Atmospheric pressure is greater than the pressure inside the jar and pushes the plastic in. Rising atmospheric pressure indicates improving weather. Slowly rising pressure indicates good weather that sticks around for several days. A quick rise in pressure means you can expect good weather, but only for a day or so.
- Burch, David F. (2009). The Barometer Handbook: A Modern Look at Barometers and Applications of Barometric Pressure. Seattle: Starpath Publications. ISBN 978-0-914025-12-2.
- Holton, James R. (2004). An Introduction to Dynamic Meteorology – Volume 1. Academic Press. ISBN 978-0-12-354015-7.
- Middleton, W. E. Knowles. (2002). The History of the Barometer (new ed.). Baltimore: Johns Hopkins Press. ISBN 0-8018-7154-9.
- Pearce, Robert Penrose (2002). Meteorology at the Millennium. Academic Press. ISBN 978-0-12-548035-2.