| Back | The atmosphere is a layer of air that surrounds Earth. It is thin compared to the size of the Earth. Atmospheric pressure is created on a surface by air molecules colliding with the surface. As the altitude (height above Earth) increases, atmospheric pressure decreases, as shown on certain graphs. These graphs are curved because atmospheric pressure is affected by the density of the atmosphere, which also varies with height. As the altitude increasesm the atmosphere gets less dense, so there are fewer aur molecules that are able to collide with the surface. There are also fewer air molecules above a surface as the height increases. This means that the wiehgt of the air above it, which contributes to atmospheric pressure, decreases with altitude. |