Definition
The drop in pressure that occurs when a moving fluid (such as air) passes through a narrowed section of a passage. As the fluid speeds up to get through the constriction, its static pressure falls.
Plain English
When air flows through a narrow spot, it speeds up and its pressure drops. The tighter the squeeze, the faster the flow and the lower the pressure at that point.
Context Anchor
Seen in instrument-system discussions, especially when an alternate static source uses cabin air instead of the normal outside pressure source.
Derivation
Named after Giovanni Battista Venturi, an 18th-century Italian physicist who studied how fluids behave when forced through a constriction. Knowing it's a person's name, not a Latin term, helps avoid hunting for a hidden meaning in the word.
Why Pilots Care
It explains how certain blockages produce erroneous airspeed and altitude indications during flight.
Analogy
Similar to water pressure falling inside a garden hose when you partially cover the open end with your thumb.
Grounding Statement
Picture squeezing a garden hose: the water shoots out faster where the hose is pinched. Air does the same thing -- it speeds up through the narrow spot, and its pressure drops while it's there.
Intuition Check
The venturi effect is not a separate suction force. It is lower pressure caused by faster-moving air.
Example Sentence 1
The shape of the wing uses the venturi effect to lower the pressure on top, which helps create lift.
Example Sentence 2
Understanding the venturi effect helps pilots recognize why an altimeter may overread after a static port blockage.