How do high- and low-pressure areas...

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How do high- and low-pressure areas form, and how can the air pressure change from one place to another at sea level?
The sun’s heat is the origin of all our weather. It causes air masses to form and circulate in the atmosphere, which then causes differences in pressure. These air masses are composed of billions of molecules that are constantly moving in all directions, bouncing off whatever they encounter and creating what is known as air pressure or barometric pressure. As a warm air mass rises, it cools and spreads. This rising air causes a low-pressure area to form underneath it; there are fewer molecules and more space between them in this area. Once the air cools, it starts to sink back to Earth, thus compacting the molecules and causing an area of higher pressure.