Pascal's Principle
Pressure applied to a fluid is transmitted everywhere in it.
About this topic
Pascal's principle says that a pressure change applied to an enclosed incompressible fluid is transmitted undiminished throughout the fluid. In a hydraulic system, a small force on a small piston creates the same pressure as a large force on a large piston: F₁/A₁ = F₂/A₂. This acts as a force multiplier.
Car brakes, garage lifts, excavator arms, dentist chairs and aircraft control surfaces all use hydraulics. Fluids work well because liquids are almost incompressible, so pushing in one end moves the other end directly. Brake fluid carries your foot's force to all four wheels at once.
Worked example: a car jack has a small piston of area 0.001 m² and a large piston of area 0.05 m². Pushing with 200 N on the small piston gives a pressure of 200,000 Pa, so the large piston exerts 200,000 × 0.05 = 10,000 N, enough to lift a 1000 kg car.
Energy is not created: the small piston must move 50 times further than the large one, because work in equals work out, force times distance. Air bubbles ruin hydraulic brakes because gas compresses, which is why brakes need bleeding. A misconception is that the system gives free energy; it only trades force for distance.
Key ideas
- Hydraulic lifts multiply force
- F₁/A₁ = F₂/A₂
- Brakes use hydraulics
Quick check
Use cases: where Pascal's Principle helps
- Homework: review the key idea behind Pascal's Principle before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Pascal's Principle without notes.
- Visual learning: play with the interactive lab to see how Pascal's Principle changes when you adjust its inputs.
- Teaching a friend: explain Pascal'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 Pascal's Principle?
Pressure applied to a fluid is transmitted everywhere in it.
What will I learn in Pascal's Principle?
Hydraulic lifts multiply force. F₁/A₁ = F₂/A₂. Brakes use hydraulics.
Is Pascal'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 Pascal'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 Pascal'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.