Topicm288f92b46c4b82cf_1528449000663_0Topic

Pascal’s lawPascal’s lawPascal’s law

Levelm288f92b46c4b82cf_1528449084556_0Level

Second

Core curriculumm288f92b46c4b82cf_1528449076687_0Core curriculum

Planning and conducting observations or experiments and inference based on their results.

V. Matter's properties. Student:
5) uses Pascal’s law, according to which the increase in external pressurepressurepressure causes the same pressure increase in the entire volume of liquid or gas.

Timingm288f92b46c4b82cf_1528449068082_0Timing

45 minutes

General learning objectivesm288f92b46c4b82cf_1528449523725_0General learning objectives

Knows the content of Pascal's law.

Key competencesm288f92b46c4b82cf_1528449552113_0Key competences

1. Providing the content of Pascal's law.

2. Determining the application of Pascal's law.

Operational (detailed) goalsm288f92b46c4b82cf_1528450430307_0Operational (detailed) goals

The student:

- provides the content of Pascal's law,

- he gives examples of devices in which Pascal's law was applied.

Methodsm288f92b46c4b82cf_1528449534267_0Methods

1. Learning by observation.

2. Cooperation between students and teacher.

Forms of workm288f92b46c4b82cf_1528449514617_0Forms of work

1. Individual work.

2. Work with the whole class.

Lesson stages

Introductionm288f92b46c4b82cf_1528450127855_0Introduction

Task 1

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?

Answer:

1. Pressure is the ratio of the force to the surface area on which this force acts. The force is perpendicular to the surface.
2. The unit of pressure is PascalpascalPascal.
3. It is the same at every point of the bicycle wheel tube.
4. The particles are in motion in liquids and gases. The movement of particles is chaotic. Interactions between particles in liquids are stronger than in gases.

Procedurem288f92b46c4b82cf_1528446435040_0Procedure

Task 2

Follow the demonstration of the experiment carried out by the teacher.

Experiment demonstration:

Research problem:
Is the pressurepressurepressure caused by the external force the same in the entire volume of the liquid?

Hypothesis:
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.

Requisites:

- a syringe with a thick needle;
- needle or pin;
- water;
- ping‑pong ball.

Course of experiment:

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.

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

[Illustration 1]

Conclusion:
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.m288f92b46c4b82cf_1527752263647_0The 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:
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.

Task 3

See the presented model of the device:

[Illustration 2]

Task 4

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?

Answers:

a) The larger plunger will move up.
b) The pressure in these arms is the same.
c) Pascal's law is illustrated in this model

Task 5

Look at the picture:

[Illustration 3]

$\overrightarrow{F_1}$ – the force that acts on the smaller pistonpistonpiston,
$\overrightarrow{F_2}$ – the force that acts on the larger piston,
SIndeks dolny 1₁ – the area of the smaller piston,
SIndeks dolny 2₂ – the area of the larger piston,
p – the pressure inside the liquid $p=p_1=p_2=\frac{F_1}{S_1}=\frac{F_2}{S_2},$
pIndeks dolny 1₁ - pressure exerted by the smaller piston $p=p_1=p_2=\frac{F_1}{S_1}=\frac{F_2}{S_2},$
pIndeks dolny 2₂ - pressure exerted by the smaller piston $p=p_1=p_2=\frac{F_1}{S_1}=\frac{F_2}{S_2}.$

$\left[Pa=\frac{N}{m^2}\right]$

Task 6

Familiarize yourself with the practical use of Pascal's law in the industry: slideshow Hydraulic press – stamping car sheet metal, and in everyday life with respect to car operation: slideshow Pascal’s law application for hydraulic brakes.m288f92b46c4b82cf_1527752256679_0Familiarize yourself with the practical use of Pascal's law in the industry: slideshow Hydraulic press – stamping car sheet metal, and in everyday life with respect to car operation: slideshow Pascal’s law application for hydraulic brakes.

[Slideshow 1]

[Slideshow 2]

Lesson summarym288f92b46c4b82cf_1528450119332_0Lesson 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 $\overrightarrow{F_2}$ obtained by means of the press is as many times greater than the force $\overrightarrow{F_1}$ acting externally on the pistonpistonpiston, as many times the surface SIndeks dolny 2₂ of the larger piston is larger than the surface SIndeks dolny 1₁ of the smaller piston:

Selected words and expressions used in the lesson plan

hydraulic presshydraulic presshydraulic press

pascalpascalpascal

Pascal’s lawPascal’s lawPascal’s law

pistonpistonpiston

pressurepressurepressure