MAKE YOUR OWN BAROMETER II
Stretch a piece of balloon over the glass jar.
Glue a straw sideways from the center of the balloon to the end of the jar.
Glue a toothpick to the end of the straw.
On an index card write High on top and Low on the bottom near the toothpick's point. Watch and see what happens.
Barometers keep track of air pressure. When air pressure is high (which means fair weather), the toothpick will point up because air will be pressing down on the balloon. When air pressure is low (which means stormy weather is coming), the toothpick will point down because air inside the jar will be pushing up against the balloon.