Why do two sheets of paper move together when air is blown between them?

When you blow air between two sheets of paper, they move toward each other due to Bernoulli’s theorem. This principle states that for a flowing fluid—such as air—an increase in the fluid's velocity is associated with a decrease in its pressure.12

As you blow air into the space between the sheets, the air velocity in that gap becomes higher than the velocity of the stationary or slower-moving air on the outer sides of the sheets. According to the theorem, this higher velocity creates a region of lower pressure between the papers. Because the atmospheric pressure on the outer sides of the sheets remains higher than the reduced pressure in the gap, the sheets are pushed toward each other. This phenomenon is a classic demonstration of how pressure changes act as the cause for velocity changes in fluid mechanics.2