While air can be compressed more easily than water, freely flowing air acts much like water—at least at relatively low speeds. So when you squeeze a stream of air, two things happen. The air speeds up, and as it speeds up, its pressure—the force of the air pressing against the side of the object—goes down. When the air slows back down, its pressure goes back up. Why does the air speed up? Because of conservation of mass, which states that mass is neither created nor destroyed, no matter what physical changes may take place.