Bernoulli's Principle
Faster fluid flow means lower pressure.
About this topic
Bernoulli's principle states that, along a streamline in steady flow, faster-moving fluid has lower pressure, a consequence of energy conservation: P + ½ρv² + ρgh is constant. Where a pipe narrows the fluid speeds up and the pressure drops. The continuity equation, A₁v₁ = A₂v₂, tells us how much the speed rises.
It helps explain how aircraft wings generate lift, with faster air over the curved top giving lower pressure than below, and how perfume sprayers, carburettors and Venturi meters work. Curveballs swerve and shower curtains blow inward for related reasons. Chimneys draw better on windy days because fast wind across the top lowers the pressure.
Worked example: water flows at 2 m/s through a pipe that narrows to one quarter of its area. By continuity the speed rises to 8 m/s, and the pressure drops by ½ × 1000 × (8² − 2²) = 30,000 Pa.
Be careful: Bernoulli applies to steady, smooth flow of nearly frictionless fluids, and a full explanation of lift also involves the wing deflecting air downward. A frequent misconception is the equal-transit-time story that air must meet at the back at the same time, which is false. Another is that fast flow always means low pressure in any situation, such as inside a fan blast.
Key ideas
- Explains wing lift and spray bottles
- Energy conservation for fluids
- Continuity: A₁v₁ = A₂v₂
Quick check
Use cases: where Bernoulli's Principle helps
- Homework: review the key idea behind Bernoulli's Principle before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Bernoulli's Principle without notes.
- Visual learning: play with the interactive lab to see how Bernoulli's Principle changes when you adjust its inputs.
- Teaching a friend: explain Bernoulli's Principle in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Bernoulli's Principle?
Faster fluid flow means lower pressure.
What will I learn in Bernoulli's Principle?
Explains wing lift and spray bottles. Energy conservation for fluids. Continuity: A₁v₁ = A₂v₂.
Is Bernoulli's Principle part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Bernoulli's Principle lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Bernoulli's Principle?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.