# Air Pressure

Atmospheric pressure is a force in an area pushed against a surface by the weight of air in Earth’s atmosphere. The Earth is covered in a layer of air. However, this layer is not distributed evenly around the globe. At different times, the layer of air is thicker in some places than in others. Where the layer of air is thicker, there is more air. Since there is more air, there is a higher pressure in that spot. Where the layer of air is thinner, there is a lower atmospheric pressure.

The higher the altitude, the thinner the air is, and the lower the atmospheric pressure is. This is because high places do not have as much air above them, pushing down.

Barometers can be used to measure atmospheric pressure.

Here’s one type of barometer. The air pushes down with however much pressure is in the air. That pushes the liquid up the tube. The measurement of how high the liquid is in the tube shows how much air pressure there is. Low pressure usually means rain. High pressure means clear skies. You can think of the high pressure pushing and sweeping those clouds away.

Take a look at the interesting pictures below and read about them.

This plastic bottle was sealed at approximately 14,000 feet altitude, and was crushed by the increase in atmospheric pressure (at 9,000 feet and 1,000 feet) as it was brought down towards sea level.
Do you see that the air is crushing the bottle? It’s happening because the air pressure on the outside is higher than on the inside. It’s pressing in harder from the outside than it is from the inside.