Air has weight. You might not be able to see it, but it is everywhere Air has weight. You might not be able to see it, but it is everywhere. It touches everything and presses against everything. This is called air pressure.

Air molecules exert the pressure. All of the air above the Earth’s surface is pulled towards the planet by the force of gravity.

As you see in the drawing, atoms have a lot of space between them As you see in the drawing, atoms have a lot of space between them. They can be compressed to fit into areas of smaller volume. When air is compressed, it is called high pressure.

Air pressure tends to be higher close to the earth’s surface where the molecules are compressed by the air above. Air pressure drops as the altitude increases and the amount of air decreases.

A barometer is used to measure air pressure. Local air pressure can change due to the wind and weather.

Meteorologists know that if a low air pressure system moves into an area, they can expect wind, clouds and some form of precipitation.

A high air pressure system usually brings fair and sunny weather with it.