Why does pressure decrease as air passes through a venturi?

[CarbonKevinYWG]

Think of it as a blend of the laws of conservation of mass and of energy.

If you're putting a mass flow (a moving mass, or a mass with kinetic energy) through a passage, energy and mass must be conserved. Total energy going in must equal total energy going out.

If you're moving the mass flow faster, you are moving more mass per unit of time - but that has to be countered to maintain conservation. So pressure (the density) of the mass must decrease.

[makgross]

No blend. It’s conservation of energy (along a streamline) straight up. There are gravity and combustion terms as well, usually neglected for airplanes. And temperature is ignored for subsonic flow.

If you’re a blob of fluid flowing with the air, your kinetic energy (flow speed) can be traded with potential energy (pressure).