# Bernoulli's principle Bernoulli's principle says that along a streamline in a steady, frictionless, incompressible flow, pressure falls where speed rises. It is [[Energy]] conservation written for a moving fluid: the sum of pressure, kinetic, and potential terms is constant along the line. Stated with its conditions attached it is exact and enormously useful; stated without them it is the most misapplied result in [[Fluid_dynamics]]. ## What the conditions exclude Along a streamline is the crucial phrase — the constant differs between streamlines unless the flow is also irrotational, which means [[Vorticity]] free. It fails wherever [[Viscosity]] is doing work, so it says nothing inside a [[Boundary_layer]] or across a [[Hydraulic_jump]], both of which dissipate [[Energy]]. And it does not by itself explain lift: the popular equal-transit-time story attaches Bernoulli to a false premise, and the honest account runs through [[Circulation_(physics)|circulation]] and the [[Kutta–Joukowski_theorem]]. Bernoulli describes the pressure field; it does not supply the [[Velocity]] field that produced it. ## Instruments built on it A Venturi narrows a pipe, speeds the flow, and reads the pressure drop as a flow rate. A pitot tube compares stagnation with static pressure to give airspeed — the primary sensor behind every [[Avionics|air-data]] display, and a known [[Reliability_engineering|failure point]] when it ices or blocks. Carburettors, atomisers, and aspirators all use the same low-pressure throat, as does a [[WT!Advanced_Manufacturing_Center_of_Excellence|shop]] vacuum ejector running on compressed air. **Microsim brief (next pass):** Venturi tube with a flow slider; live pressure trace along the length and manometer columns that rise and fall, plus a toggle for the incorrect equal-transit-time animation beside the correct one. **On the spine:** [[Fluid_dynamics]] · [[Potential_flow]] · [[Boundary_layer]] · [[Kutta–Joukowski_theorem]] · [[Cavitation]] · [[WT!Thury_Hydrodynamics_Compendium]]. <!-- SPINEPATH:BEGIN g20 — shortest chain of Wikipedia links between local articles to a Compendium Main article; do not hand-edit inside --> *Connected to the Apex Spine:* Bernoulli's principle → [[Fluid_dynamics|Fluid dynamics]] — [[WT!Thury_Hydrodynamics_Compendium|Compendium]] section 1, *Fluid dynamics*. <!-- SPINEPATH:END --> <!-- COMPENDIUMLINK:BEGIN g19 — generated from _registry/plans/THURY_COMPENDIUM_SECTIONS.md; do not hand-edit inside --> **Part of the [[WT!Thury_Hydrodynamics_Compendium|Thury Hydrodynamics Compendium]]** — main article for section 22, *Energy along a streamline*. Related sections: [[Fluid_dynamics]] · [[Hydrostatics]] · [[Boundary_layer]]. <!-- COMPENDIUMLINK:END --> <!-- THURYSIM:BEGIN g21 — Thury Compendium microsim (framework build, specs/sims/Bernoulli's_principle.json); do not hand-edit inside --> **Microsim — three.js (Wikitube framework):** *Bernoulli's principle* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/thury/Bernoulli's_principle.html" data-title="Bernoulli's principle"></div> *Built from `MICROSIM_GUIDE/specs/sims/Bernoulli's_principle.json`; part of the [[WT!Thury_Hydrodynamics_Compendium|Thury Hydrodynamics Compendium]] set.* <!-- THURYSIM:END --> ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Bernoulli's_principle) : [Wikitube](https://en.wikitube.io/wiki/Bernoulli's_principle) ## Previous hub tags Hubs: `Life_Physics`, `Systems`. Portals: [[PORTAL_WT!Thury_Hydrodynamics_Compendium]], [[PORTAL_Physics]]. --- *Fluid seed wave · 2026-09-10 · seed register · microsim layer pending.*