| HIGH/LOW PRESSURE | |
| Atmospheric pressure is defined as the force per unit area exerted against a surface by the weight of the air above that surface. Did you get that? Really, all it is is the weight of the air. When the pressure is high, it means that there is more air pushing down on the earth. When the pressure is low, the opposite is true, less air is pushing down. Warmer areas are usually under less pressure than colder areas, and vice versa. To understand this, think of a hot-air balloon. When you heat the air inside the ballon, it expands and wants to go up because it's lighter. Less weight is like low pressure.
The different pressures create wind, because when warm air rises, cold air rushes in to take it's place. The thin lines you see on the map are called isobars. They surround areas of the same pressure. The closer the lines are to each other, the faster the wind is blowing. Atmospheric pressure is measured with an instrument called a "barometer", which is why atmospheric pressure is also referred to as barometric pressure. |  |
