What is Bernoulli's principle?

Bernoulli's principle: P + ½ρv² = constant. When a fluid speeds up, its pressure drops, and when it slows down, its pressure rises. Each litre of flowing water or air keeps the same total energy, shared between pressure, motion and height.

Read how it works: What is Bernoulli's principle? · The history of Bernoulli's principle · More boxes on Glassbox

Chapters in this interactive model

1. Faster flow, lower pressure: Squeeze water through a narrow neck. It speeds up, and its pressure drops.
2. Suck it up: Fast air has low pressure, and the still air around pushes a liquid into it.
3. Squeeze it out fast: Push a fluid through a small hole and its pressure becomes speed: v = √(2Δp/ρ).
4. Air that bends and follows: How a wing really lifts, why cyclists tuck in behind, and a ball that floats in a jet.
5. When the rule bends: Friction, speeds near sound, and the myth of air that has to meet up again.