Topicmcaef80b897d693da_1528449000663_0Topic

Archimedes’ principleArchimedes’ principleArchimedes’ principle

Levelmcaef80b897d693da_1528449084556_0Level

Second

Core curriculummcaef80b897d693da_1528449076687_0Core curriculum

I. The use of physical concepts and quantities to describe phenomena and to indicate their examples in the surrounding reality.

V. Matter's properties. Student:
9c) demonstrates the Archimedes’ principle and on this basis analyses the floating of bodies; determines the density of liquids or solids.

Timingmcaef80b897d693da_1528449068082_0Timing

45 minutes

General learning objectivesmcaef80b897d693da_1528449523725_0General learning objectives

Using the concept of buoyant forcebuoyant forcebuoyant force.

Key competencesmcaef80b897d693da_1528449552113_0Key competences

1. Recognition of characteristics describing buoyant force.

2. Using Archimedes' principle.

3. Presenting examples of the use of Archimedes' principle.

Operational (detailed) goalsmcaef80b897d693da_1528450430307_0Operational (detailed) goals

The student:

- recognizes the buoyant force and its characteristics,

- gives the content of Archimedes' principle and examples of its application.

Methodsmcaef80b897d693da_1528449534267_0Methods

1. Learning by observation.

2. Learning by experimenting.

Forms of workmcaef80b897d693da_1528449514617_0Forms of work

1. Individual work.

2. Work with the whole class.

Lesson stages

Introductionmcaef80b897d693da_1528450127855_0Introduction

We already know that the hydrostatic pressure depends on the height of the liquid column, the density of the liquid and the standard gravity.

We measure body density as a ratio of body mass to its volume.

We measure the weightweightweight of a body using a dynamometer or a suitable weight.

Proceduremcaef80b897d693da_1528446435040_0Procedure

Task 1

Observe the experiment performed by the teacher.

Experiment 1

Research problem:
Does water affect the weightweightweight of the body immersed in it?

Research hypothesis:
The real weight of the body does not change, but the apparent weight of the body immersed in water is smaller than the weight of the same body in the air.

Requisites:

a) dynamometer;
b) tripod;
c) cuboids of the same dimensions, made of various metals, e.g. copper, aluminium and iron;
d) beaker with water.

Course of the experiment:

1. Using a dynamometer, determine the weightweightweight of this cuboid.
2. Record the result in the table.
3. Immerse the suspended cuboid completely in a beaker of water; do not immerse the hook of the dynamometer itself.
4. Read the result again and record the dynamometer readings.
5. Make the same measurements for the other cuboids.

Save the results of the experiment in the table.

[Table 1]

Observation:
Experiment has shown that the dynamometer reading during the measurement when the body was immersed in water is smaller than during the measurement when it was in the air.

[Illustration 1]

Conclusions:

- The difference between measurements does not depend on the material from which the rectangles are made, and is always constant, provided that their volumes are the same.
- The observed regularity applies to all liquids.
- An additional force acts on the body immersed in any liquid, which has the opposite direction with respect to the force of gravity.
- This force is called the buoyancy force, and its value does not depend on the type of substance from which the immersed body is made.mcaef80b897d693da_1527752263647_0- The difference between measurements does not depend on the material from which the rectangles are made, and is always constant, provided that their volumes are the same.
- The observed regularity applies to all liquids.
- An additional force acts on the body immersed in any liquid, which has the opposite direction with respect to the force of gravity.
- This force is called the buoyancy force, and its value does not depend on the type of substance from which the immersed body is made.

Task 2

Give the names of the forces shown in the figure:

[Interactive graphics]

Task 3

Perform the experiment according to the given scheme.

Experiment 2

Research problem:
What determines the buoyant forcebuoyant forcebuoyant force?

Observations:

a) The buoyant force depends on the type of liquid in which the body is completely immersed.

[Illustration 2]

b) The buoyant force depends on the volume of the immersed body.

[Illustration 3]

Task 4

Perform the experiment according to the given scheme.

Experiment 3

Perform the experiment under the supervision of an adult.

Research problem:
What does the buoyant force depend on?

Hypothesis:
The buoyant forcebuoyant forcebuoyant force does not depend on the body shape, liquid volume, immersion depth, body weightweightweight

Requisites:

a) beakers of various volumes,
b) water,
c) dynamometer,
d) plasticine ball,
e) cord.

Instruction:

1. Hang the ball on a cord.
2. Determine the weightweightweight of the ball with a dynamometer.
3. Immerse the ball completely in beakers of various volumes of water.
4. Read the dynamometer readings.
5. Immerse the ball in water - read the dynamometer readings.
6. Change the shape of the ball and repeat step 5.
7. Immerse the ball in a measuring cylinder filled with water and read the value of the buoyant force at the different depth of the ball's immersion.

Observations:

a) The buoyant force does not depend on the shape of the body (point 6 of the instructions).

[Illustration 4]

b) The buoyant force does not depend on the volume of liquid in which it is immersed (point 3 of the instructions).

[Illustration 5] 

c) The buoyant force does not depend on the immersion depth of the body (point 7 of the instructions).

[Illustration 6] 

Conclusions:

The buoyant forcebuoyant forcebuoyant force acting on the body immersed in the liquid depends on the density of the liquid and the volume of the immersed body. The buoyant force does not depend on the shape of the body, body weightweightweight, liquid volume, immersion depth. 

Based on the above‑mentioned experiments, we can formulate the content of Archimedes' principle:

For every body immersed in a liquid there is a buoyant force which is directed upward and equal in magnitude to the weight of the displaced liquiddisplaced liquiddisplaced liquid. 

The magnitude of buoyant force FIndeks dolny w  Indeks dolny koniec_w is calculated according to the formula:

where:
d - density of displaced liquid;
V - volume of displaced liquid;
g - standard gravity.

Task 5

Answer the question:

Is Archimedes' principle valid for bodies immersed in gas?

Suggest a way to confirm the validity of the principle for gases.

Answer:

a) Archimedes' right is also valid for bodies immersed in gas because the volume of gas displaced by the body also has its own weight.

b) Archimedes' principle for gases can be checked with a balloon filled with hydrogen or helium.

Lesson summarymcaef80b897d693da_1528450119332_0Lesson summary

1. The buoyant force affects the body immersed in liquid or gas.

2. The buoyant force is always directed upward

3. The buoyant force depends on the density of the liquid or gas and the volume of the body immersed in the liquid or gas.

4. Archimedes' principle:
For each body immersed in a liquid (or gas), there is a buoyant force that is directed upward and equal in magnitude to the weight of the displaced liquid (or displaced gas).

5. The buoyant force can be calculated using the formula:

where:
d - density of displaced liquid,
V - volume of displaced liquid,
g - standard gravity.

Selected words and expressions used in the lesson plan

Archimedes’ principleArchimedes’ principleArchimedes’ principle

buoyant forcebuoyant forcebuoyant force

depth of immersiondepth of immersiondepth of immersion

displaced liquiddisplaced liquiddisplaced liquid

displaced volumedisplaced volumedisplaced volume

force of gravityforce of gravityforce of gravity

weightweightweight