How Everything Works
How Everything Works How Everything Works

Question 963

What is a barometer, how does it work, and why is it useful in predicting the weather? — HC
A barometer measures air pressure by examining the forces that air exerts on surfaces. The higher the air pressure, the more force air will exert on a certain surface. Most barometers compare the present air pressure with a known pressure by putting those two pressures on opposite sides of a flexible surface. The higher the air pressure, the more that surface will bend away from it.

You can make a simple barometer by inserting a drinking straw in narrow-mouthed jar that's half full of water and by sealing the neck of the jar around the straw (with a rubber stopper, wax, or glue). Make sure that the end of the straw is immersed in the water and that the water level in the straw is above the top of the jar. As the outside air pressure decreases, the trapped air inside the jar will push the water farther up the straw. As the air pressure increases, it will push the water farther down the straw. Try to keep your barometer's temperature constant, because temperature will also affect its water level. You can use your barometer to predict the weather (somewhat) because storms tend to be accompanied by lower air pressures.


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