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Pascal’s principle of transmission of fluid pressure

Source: licencja: CC 0.

Prawo Pascala

You will learn
  • Pascal's law and its application,

  • learn the content of Pascal's law and its practical application with the use of English vocabulary.

Exercise 1
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Answer the questions.

1. Provide a pressurepressurepressure definition.
2. Enter the pressure unit.
3. Is the pressure in the tube of the bicycle wheel in each point of the inner tube the same?
4. Are molecules in liquids and gases in motion or at rest?

Experiment demonstration
Experiment 1
Research problem
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Is the pressure caused by the external force the same in the entire volume of the liquid?

Hypothesis
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If we exert pressure on the liquid or gas from the outside, it will create in the liquid or gas an additional pressure equal in the entire volume of this liquid or gas.

You will need
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- a syringe with a thick needle,
- needle or pin,
- water,
- ping‑pong ball.

Instruction
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1. Using a pin, make holes in the ball - evenly over its entire surface.
2. Fill the syringe with water.
3. Pierce the surface of the ball with the needle and push it in quite deeply.
4. Fill the ball with water from the syringe. If there is not enough water in the syringe, disconnect it from the needle, fill with water again, connect it with the needle and fill the ball until it is full.
5. When the ball and syringe are filled with water, press the plunger of the syringe.
6. Observe the water jets squirting from the holes on the surface of the ball.

Summary
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We see that from every hole in the ball the water squirts in the same way.

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Source: GroMar, licencja: CC BY 3.0.
Conclusion
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The force with which we press on the plunger of the syringe produces the same pressure in the entire volume of the liquid. From each hole of the ball (located at the bottom, side, top), the water squirts in the same way. This shows that the pressure caused by pressing the plunger is the same in each of the holes regardless of whether the hole is on the bottom, side or top of the ball.

Pascal's law
Definition: Pascal's law
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If we exert pressurepressurepressure on the liquid or gas from the outside, it will create in the liquid or gas an additional pressure equal in the entire volume of this liquid or gas.

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See the presented model of the device.

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Source: GroMar, licencja: CC BY 3.0.
Exercise 2
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Answer the questions.

a) How will the bigger piston behave if we press a smaller piston with our hand?
b) Is the pressure in both arms of the vessel the same?
c) Is Pascal's law illustrated in the presented model?

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Look at the picture.

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Source: GroMar, licencja: CC BY 3.0.
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F1 – the force that acts on the smaller pistonpistonpiston,
F2 – the force that acts on the larger piston,
SIndeks dolny 1 – the area of the smaller piston,
SIndeks dolny 2 – the area of the larger piston,
p – the pressure inside the liquid p=p1=p2=F1S1=F2S2,
pIndeks dolny 1 - pressure exerted by the smaller piston p=p1=p2=F1S1=F2S2,
pIndeks dolny 2 - pressure exerted by the smaller piston p=p1=p2=F1S1=F2S2.

Pa=Nm2

Task 1
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Familiarize yourself with the practical use of Pascal's law in the industry: slideshow „Hydraulic presshydraulic pressHydraulic press – stamping car sheet metal”, and in everyday life with respect to car operation: slideshow „Pascal’s lawPascal’s lawPascal’s law application for hydraulic brakes”.

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Pokaz multimedialny - prasa hydrauliczna - tłoczenie blachy samochodowej. Instrukcja obsługi z poziomu klawiatury: 1. Uruchomienie aplikacji - ENTER, 2. Na każdym ze slajdów czytany jest automatycznie tekst alternatywny po polsku, 3. Przy pierwszym uruchomieniu na pierwszym slajdzie, czytanie tekstu po angielsku - TAB, 4. Przejście między slajdami: do następnego slajdu - TAB, do poprzedniego slajdu - TAB + SHIFT, 5. Przejście do czytania napisu po angielsku - strzałka w górę + strzałka w dół (czyta tekst po angielsku widoczny na slajdzie).
Source: GroMar, licencja: CC BY 3.0.
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Pokaz multimedialny - prawo Pascala w zastosowaniu do hamulców hydraulicznych. Instrukcja obsługi z poziomu klawiatury: 1. Uruchomienie aplikacji - ENTER, 2. Na każdym ze slajdów czytany jest automatycznie tekst alternatywny po polsku, 3. Przy pierwszym uruchomieniu na pierwszym slajdzie, czytanie tekstu po angielsku - TAB, 4. Przejście między slajdami: do następnego slajdu - TAB, do poprzedniego slajdu - TAB + SHIFT, 5. Przejście do czytania napisu po angielsku - strzałka w górę + strzałka w dół (czyta tekst po angielsku widoczny na slajdzie).
Source: GroMar, licencja: CC BY 3.0.
Summary
  • If the force acts on the liquid or gas from outside, it will create in the liquid or gas an additional pressurepressurepressure equal in the entire volume of this liquid or gas. We say that the external pressure exerted on the liquid spreads equally in all directions. This law was formulated by Blaise Pascal and is named Pascal's law after his name.

  • Pascal's law has been widely used, among others in the design of presses, car jacks, pumps and hydraulic braking systems.

  • The principle of operation of the hydraulic press uses Pascal's law. The task of the press is to multiply the external force and use it to do the work.

  • The magnitude of the force F2 obtained by means of the press is as many times greater than the force F1 acting externally on the pistonpistonpiston, as many times the surface SIndeks dolny 2 of the larger piston is larger than the surface SIndeks dolny 1 of the smaller piston:

    p=F1S1=F2S2

Exercises

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Exercise 3
Exercise 4

The large piston of the hydraulic press moves in one stroke by h = 45 cm and a small one by hIndeks dolny 1 = 4 cm. Calculate the value of the force that a large piston acts on the body if the force F = 200 N acts on the small piston. Draw the device diagram. Mark the given quantities in the drawing.

Exercise 5

Write in English what is the reason that by pumping the wheel of a bicycle we must act with larger and larger force?

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Exercise 6
Wersja alternatywna ćwiczenia: Indicate which pairs of expressions or words are translated correctly. Możliwe odpowiedzi: 1. tłok - pressure, 2. prasa hydrauliczna - hydraulic press, 3. prawo Pascala - Pascal’s law, 4. paskal - pascal, 5. ciśnienie - piston
zadanie
Source: GroMar, licencja: CC BY 3.0.
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Interaktywna gra, polegająca na łączeniu wyrazów w pary w ciągu jednej minuty. Czas zaczyna upływać wraz z rozpoczęciem gry. Jeden ruch to odkrywanie najpierw jednej potem drugiej karty z wyrazem. Każdy wyraz jest odczytywany. Kolejny ruch to odkrywanie trzeciej i czwartej karty. W ten sposób odsłuchasz wszystkie wyrazy. Nawigacja z poziomu klawiatury za pomocą strzałek, odsłuchiwanie wyrazów enterem lub spacją. Znajdź wszystkie pary wyrazów.
Source: Zespół autorski Politechniki Łódzkiej, licencja: CC BY 3.0.

Glossary

hydraulic press
hydraulic press

prasa hydrauliczna

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wymowa w języku angielskim: hydraulic press
pascal
pascal

paskal

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wymowa w języku angielskim: pascal
Pascal’s law
Pascal’s law

prawo Pascala

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wymowa w języku angielskim: Pascal’s law
piston
piston

tłok

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wymowa w języku angielskim: piston
pressure
pressure

ciśnienie

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wymowa w języku angielskim: pressure

Keywords

hydraulic presshydraulic presshydraulic press

Pascal’s lawPascal’s lawPascal’s law

pressurepressurepressure