Hang two sheets of paper vertically from adjacent corners. The sheets should be parallel and close to each other with a small gap between them. Now gently blow down between the two sheets. What happens? a. The sheets move toward each other and the gap narrows. b. The sheets move away from each other and the gap widens c. Nothing happens. The gap between the two sheets remains constant.

This exercise is related to fluid mechanics, when blowing between the two sheets, we can apply Bernoulli's equation, where the index 2 is the space between the two sheets

P₁ + ½ ρ g v₁² + ρ g y₁ = P₂ + ½ ρ g v₂² + ρ g y²

if the two leaves are at the same height

y₁ = y₂

whereby

P₁ + ½ ρ g v₁² = P₂ + ½ ρ v₂²

for the air velocity between the leaves let us use the continuity equation

A₁ v₁ = A₂ v₂

the area between the leaves is less than the external area, so the air speed must increase. If we use this in Bernoulli's equation, increasing the speed 2 (between the leaves) to maintain equality the pressure must decrease.

If the pressure decreases, the blades should move closer

When resisting the answers, the correct one is a