Science Fair Project: Chemistry
BUILD A HOME BAROMETER
When you watch the evening news, the weather reporters often refer to the barometric pressure as an indicator of both current conditions and the predicted weather. In particular, they will tell you if the pressure is rising or falling. Generally, falling pressure, or the presence of a low pressure system, indicates bad weather, and rising pressure, or the presence of a high pressure system, indicates improving weather. When air warms up, pressure tends to increase, while cooling air is usually accompanied by lower pressure. You will also find this if you climb a mountain. At the higher elevations, the air is thinner, which means the pressure is lower, and the air is also usually cooler.
It's not hard to build your own barometer that will allow you to predict the weather from the comfort of your own home.
How does a barometer work?
You will be building your own home barometer, which will allow you to track the weather over several days and predict the weather to come. You will be using water levels in an empty 2-liter bottle to record the rise and fall of the atmospheric pressure. After you gather a few days' worth of data, you'll be able to compare your predictions to those of the local weather forecasters!
Barometers are used to measure the air pressure outside at any given time. They can also be used to predict the weather. This requires tracking pressure values over time to determine if there is a trend toward increased pressure or toward lowered pressure.
By measuring the height of the water in your bottle due to the air pressure outside the bottle, you'll have a way to compare one day's value to another. Over time, you can use the changing heights to make your own predictions.
Empty 2-liter plastic bottle (smaller bottles will work as well)
Knife or scissors
Use a knife or scissors to cut the bottom off the plastic bottle so that it sits evenly on the table. You may need to ask for help from an adult for this step.
Fill the pan about half full of water.
With the bottom cut off of the bottle, the cap must be screwed on and, inverted, the neck of the bottle becomes the bottom when filling. Fill the bottle with enough water so that when inverted, the water level inside the bottle is above that of the pan. It will look a little like a funnel as it is filled. Then it will be inverted and placed into the pan of water. Place the bottle in the water so that it sits evenly on the bottom of the pan. Make a small mark on the bottle indicating the height of the water.
Take a strip of paper and make a scale with evenly marked intervals. There should be a zero point on your strip of paper, with several markings above and below that mark. You will use this to track the changing heights of the water. To accurately show the small increments that you will want to measure, make your scale fairly small, perhaps starting with markings every ⅘ inch.
Attach your measuring scale to the side of the bottle, placing the zero point at the exact level of the water in the bottle.
Make one mark on your measuring scale at the beginning water level. Use your mark to indicate the date of your first measurement.
Wait 24 hours and measure again. Make another mark to represent your second measurement.
Continue measuring each day for one week. After the week has passed, take off the measuring scale, and look at your measurements.
QUESTIONS FOR THE SCIENTIST
Did the height of the water change over the week?
Did the height go up or down?
What kind of change in air pressure produces this kind of change in your water level?
What kind of weather would you predict based on the change in heights?
Did your local weather match this prediction?
Now that you have tried this experiment, you can repeat it by making more measuring scales and actually predicting the upcoming weather.
Congratulations! You are a meteorologist!
If air pressure increases, the outside air will press down on the water in the pan and push it up into the bottle. This will produce an increase in height of the water. When weather forecasters use the term “inches of mercury,” they are using a similar scale to measure the height of a different liquid due to the outside air pressure.
If the weather was pretty consistent during the course of the week, you may not have seen much change in your barometer. Don't be discouraged! Try it again, and give yourself more time. This experiment will work all year long.