A barometer is a device used to measure air pressure. In general, the pressure is higher near sea level since there is so much air above pushing down. Conversely, air pressure is lower in the mountains since there is less air above.
Elevation effects air pressure and, it is also effected by temperature. Warmer temperatures result in low pressure air since the molecules spread apart. Cold temperatures result in air molecules packed closer together and higher pressure.
Barometers and Weather
Barometers are important devices in forecasting weather. Moisture is stored in low pressure air. Therefore, if the barometer is dropping it can mean a storm is coming. Often when weathermen speak of hurricanes, low pressure is discussed.
High pressure systems are commonly associated with nice days. The high pressure keeps the moisture out, but if a high pressure hangs over an area too long it can mean drought.
Since air likes to move from areas of high pressure towards areas of low pressure, barometers can help to predict wind.
Make Your Own Barometer
Since mercury changes its size so dramatically in accordance with pressure, it is the key element in many barometers. However, since it is toxic and difficult to obtain, our barometer was constructed from an empty glass jar, balloon, straw and tape.
The barometer was placed near the wall and pressure lines were drawn onto a sheet of paper behind the barometer. Over time we could see the indicator move up and down.