MAKE A BAROMETER
Do you know what the air pressure is today? You can find out for yourself by measuring the air pressure on a barometer.
COVER the top of the can with plastic wrap. USE a rubber band to hold the plastic wrap in place. The cover should be taut making the can airtight. PLACE the straw horizontally on the plastic wrap so that two-thirds of the straw is on the can. TAPE the straw to the middle of the plastic wrap. TAPE the index card to the can behind the straw. Carefully RECORD the location of the straw on the index card. After 15 minutes, RECORD the new location of the straw on the index card. Continue CHECKING and RECORDING the straw location as often as desired. Be careful not to place your barometer near a window, as the barometer is sensitive to temperature as well as air pressure.
High pressure will make the plastic wrap cave in, and the straw go up. Low pressure will make the plastic wrap puff up, and the straw go down. Check your measurements with a real barometer. What happens to your barometer when a big storm comes? Can you use your barometer to predict a storm?