HI, I'm Gary for Expert Village.
The way the air pressure works is kind of similar to what we've seen in meteorological maps that sometimes when you're watching the news we see these big maps, we see a bunch of H's and L's and we can now understand what those things mean. When there's a high pressure we can usually expect sunshine and that is because the pressure is very high on the outside. So for our barometer what it would be doing is be pressing down on the top of the jar, pressing down giving, and putting weight on to the balloon and therefore the straw would be tilting upward and that would indicate sunny weather. Now if the air pressure is lower on the outside that means the air pressure inside the jar is greater and that would mean that the balloon would be going upwards from the bottom because of the stronger air pressure inside the jar and that would cause the straw to actually tilt downwards so now we can also understand even beyond our barometer, we can actually understand what all these weather maps mean when we take a look, what a high pressure and a low pressure zone on a weather map actually means and now we can actually see it applied when we can expect sunny or cloudy weather.