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Changing air pressure causes the weather to change. Warm air is lighter than cold air, so it rises. When warm air rises, it leaves behind
an area of low pressure. As air rises, it becomes cooler and starts to sink. This makes an area of high pressure.
You can measure high and low pressure!
The tool scientists use to measure air pressure is called a barometer . You can make one with things found around your house. Here’s how:
1 balloon 1 drinking straw 1 wide-necked glass jar glue scissors string
Low pressure often brings cloudy, unsettled weather.
High pressure usually brings fair weather.
Stretch the balloon over the top of the jar. Secure it with a string.
Glue the end of the straw onto the center of the balloon.
You can use your barometer
Date
Where is the straw on the air pressure scale (barometer)?
Actual weather outside
and this chart to see if this is true!
Cut off the neck of the balloon.
Cut out the pressure scale below.
Tape the scale on a wall behind the jar so that when the straw is straight, it rests halfway between the high pressure and low pressure marks.
Standards Link: Investigation: Students know how to make a systematic observation.
Standards Link: Physical Science: Students know that states of matter depend on molecular motion. move faster and farther away from each other. This causes warm air to be lighter than cold air, so it rises. This is why hot air balloons float up into the sky. Heaters blow hot air into the balloon and it fills and rises. When balloonists want to land, they turn off the heat and float downward. Air is made of molecules. When molecules heat up, they
Over the next few days, watch the straw move up and down as the air pressure changes.
© Vicki Whiting January 2026
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