Question

Explain what causes air pressure:

Answer 1

Air pressure is caused by the weight of the air molecules above. Even tiny air molecules have some weight, and the huge numbers of airmolecules that make up the layers of our atmosphere collectively have a great deal of weight, which presses down on whatever is below.

Answer 2

Gravity pulling the mass of the atmosphere toward the center of the earth. Atmosphere includes air, water vapor, etc.