Pressure

You’ve seen that air is a mixture of different gas molecules, mostly oxygen and nitrogen, and almost all of the time, some water vapor is present.
Pressure is the term we use to describe the force of these molecules on the Earth’s surface.
You will learn a lot more about atmospheric pressure in the next module, but for now, understand that all of the gases in the atmosphere exert pressure on the Earth’s surface as they are pulled down by gravity.