🔩 Bernoulli's Principle — Venturi Effect
Where fluid speeds up, pressure drops. The Bernoulli equation P + ½ρv² + ρgh = const is conservation of energy per unit volume. Combined with the continuity equation A₁v₁ = A₂v₂, it explains carburettors, aeroplane lift, and perfume atomisers.
Flow
Results
Fluid
How it works
The continuity equation demands that fluid mass is conserved: A₁v₁ = A₂v₂. So where the pipe narrows (A₂ < A₁), velocity must increase. Bernoulli then tells us pressure must fall to keep total energy constant: P₂ = P₁ + ½ρ(v₁² − v₂²).
The Venturi meter exploits this to measure flow rate: by measuring the pressure difference ΔP between the wide and narrow sections, the flow rate Q = A₁ · √(2ΔP / ρ(1/R²−1)) is known precisely.
Real-world applications
Carburettors (air speeds up → fuel drawn in), Pitot tubes (aircraft speed), aeroplane wings (air faster over curved top → lower pressure → lift), perfume atomisers, and Bunsen burner air intake all use Bernoulli's principle.