When the body floats. Statics. Swimming conditions of bodies. III. Practical work to verify the findings

During the classes

Progress of the lesson

Self-analysis of the lesson

Activation of knowledge:

Solving research problems:

Reflection:

Lesson Plan

I. Organizational moment

II. Initial check of understanding of previously studied material

III. Practical work to verify the findings

IV. Reflection

V. Homework

Experience 1

Exercise 1.

Task 2.

Task 3.

Experience 2

Lesson type: study

Technologies used: Traditional, group, innovative.

The purpose of the lesson: Find out the conditions for the floating of bodies depending on the density of the liquid and the body, assimilate them at the level of understanding and application, using the logic of scientific knowledge.

Tasks:

establish theoretically and experimentally the relationship between the density of the body and the liquid necessary to ensure the conditions for the floating of bodies;
continue to develop students’ ability to conduct experiments and draw conclusions from them;
development of skills to observe, analyze, compare, generalize;
nurturing interest in the subject;
nurturing culture in the organization of educational work.

Expected results:

Know: Sailing conditions tel.

Be able to: Experimentally determine the conditions for floating bodies.

Equipment: Multimedia, screen, individual task cards, density table, materials to be studied.

Teacher:

– In previous lessons, we examined the effect of liquid and gas on a body immersed in them, studied Archimedes' law, and the conditions for floating bodies. We will learn the topic of today's lesson by solving a crossword puzzle.

Horizontal: 1. Unit of division. 2. Unit of mass. 3. Multiple unit of mass. 4. Unit of area. 5. Unit of time. 6. Unit of force. 7. Unit of volume. 8. Unit of length.

Answers: 1. Pascal. 2. Kilogram. 3. Ton. 4. Square meter. 5. Hour. 6. Newton. 7. Liter. 8. Meter.

(We write down the topic of the lesson in a notebook)

Teacher: But now, before we begin solving experimental problems, let’s answer a few questions. What force occurs when a body is immersed in a liquid?

Students: Archimedes' power.

Teacher: Where is this force directed?

Students: It is directed vertically upward.

Teacher: What does Archimedean force depend on?

Students: Archimedean force depends on the volume of the body and the density of the liquid.

Teacher: And if the body is not completely immersed in the liquid, then how is the Archimedean force determined?

Students: Then, to calculate the Archimedean force, you must use the formula F A = ρ w gV, where V is the volume of that part of the body that is immersed in the liquid.

Teacher: In what ways can Archimedean force be experimentally determined?

Students: You can weigh the fluid displaced by the body, its weight will be equal to the Archimedean force. You can find the difference in dynamometer readings when weighing a body in air and in liquid; this difference is also equal to the Archimedean force. You can determine the volume of a body using a ruler or beaker. Knowing the density of the liquid and the volume of the body, we can calculate the Archimedean force.

Teacher: So, we know that any body immersed in a liquid is acted upon by the Archimedean force. Also, what force acts on any body immersed in a liquid?

Students: Gravity.

Teacher: Can you give examples of bodies that float on the surface of water? What bodies drown in water? How else can a body behave in water? What kind of bodies are these? Try to guess which floating body we are talking about now.

Today over the sea
Great heat;
And he floats in the sea
Ice Mountain.
Floats and probably
Believes:
It won't melt even in the heat.

Students: Iceberg.

Teacher: Would anything change if we instantly changed the water in the ocean to kerosene?

(Students are confused about the answers)

You can't answer this question for sure. But you already have ideas and hypotheses. Let's solve the problem together today in class: Let's find out: What are the conditions for floating bodies in a liquid.

Write down the topic of the lesson in your notebook – “Swimming conditions for bodies.”

Teacher: Guys, do you know which scientist studied the floating of bodies?

Students: Archimedes.

Teacher: Let's try to check all the information about the floating conditions of bodies experimentally by carrying out research. We have already done this when studying the force of friction. Each group will receive its own task. After completing the tasks, we will discuss the results obtained and find out the conditions for the floating bodies.

Write down all the results in your notebook. If you have any questions, please raise your hand.

(The guys receive cards with tasks and equipment to complete them – 7 options. The task options are not the same in difficulty level: the first ones are the simplest, 6 and 7 are more difficult. They are given according to the level of training.)

Tasks:

Group 1 assignment:

Observe which of the proposed bodies sink and which float in the water.
Find the density of the corresponding substances in the textbook table and compare with the density of water.
Present the results in table form.

Equipment: a vessel with water and a set of bodies: a steel nail, a porcelain roller, pieces of lead, a pine block.

Equipment: a vessel with water and a set of bodies: pieces of aluminum, organic glass, polystyrene foam, cork, paraffin.

Group 2 assignment:

Compare the depth of immersion in water of wooden and foam cubes of the same size.
Find out whether the depth of immersion of a wooden cube in liquids of different densities differs. The result of the experiment is presented in the figure.

Equipment: two vessels (with water and oil), wooden and foam cubes.

Group 3 assignment:

Compare the Archimedean force acting on each of the test tubes with the force of gravity on each test tube.
Draw conclusions based on the experimental results.

Equipment: beaker, dynamometer, two test tubes with sand (test tubes with sand should float in water, immersed to different depths).

Group 4 assignment:

“Is it possible to “make” a potato float in water? Make a potato float in water.
Explain the results of the experiment. Arrange them in the form of drawings.

Equipment: a vessel with water, a test tube with table salt, a spoon, a medium-sized potato.

Group 5 assignment:

Get a piece of plasticine to float in the water.
Make sure the piece of foil floats in the water.
Explain the results of the experiment.

Equipment: vessel with water; a piece of plasticine and a piece of foil.

Teacher: We talked about the condition of solids floating in a liquid. Can one liquid float on the surface of another?

Group 6 assignment: Observation of an oil stain floating under the action of the buoyant force of water.

Goal of the work: Observe the rise of oil immersed in water, experimentally detect the buoyant action of water, and indicate the direction of the buoyant force.

Equipment: vessels with oil, water, pipette.

Sequence of experiment:

Use a pipette to take a few drops of oil.
Lower the pipette to a depth of 3–4 cm into a glass of water.
Release the oil and observe the formation of an oil stain on the surface of the water.
Draw a conclusion based on your experience.

After completing the experiment, the results of the work are discussed and the results are summed up.

While students are completing assignments, I monitor their work and provide the necessary assistance.

Teacher: When we finish the work, move the cutlery to the edge of the table. Let's move on to discussing the results. First, let's find out which bodies float in liquid and which ones sink. (Group 1)

Students: One of them names those bodies that sink in water, the other – the bodies that float, the third compares the densities of bodies of each group with the density of water. After this, everyone comes to a conclusion together.

Conclusions:

If the density of the substance from which the body is made is greater than the density of the liquid, then the body sinks.
If the density of a substance is less than the density of a liquid, then the body floats.

(Conclusions are written in notebooks.)

Teacher: What will happen to the body if the densities of the liquid and the substance are equal?

Students: give an answer.

Let's see how bodies floating on the surface of a liquid behave. Guys group 2 looked at how bodies made of wood and foam behave in the same liquid. What did they notice?

Students: The depth of immersion of bodies is different. The foam floats almost on the surface, and the tree is slightly submerged in the water.

Teacher: What can be said about the depth of immersion of a wooden block floating on the surface of water or oil?

Students: The block sank deeper in oil than in water.

Conclusion: Thus, the depth of immersion of a body in a liquid depends on the density of the liquid and the body itself.

Let's write down this conclusion.

Teacher: Now let's find out whether it is possible to make bodies float that under normal conditions sink in water, for example, potatoes or plasticine or foil. (Group 4; Group 5)

What are you observing?

Students: They drown in the water. To make the potato float, we added more salt to the water.

Teacher: What's the matter? What happened?

Students: The density of the salt water increased and it began to push the potatoes out more strongly. The density of water increased and the Archimedean force became greater.

Teacher: Right. And the guys who performed the task with plasticine had no salt. How did you manage to get the plasticine to float in water?

Students: We made a boat out of plasticine. It has a larger volume and therefore floats. You can make a box out of plasticine, it also floats. It also has more volume than a piece of plasticine.

Conclusion: So, to make normally sinking bodies float, you can change the density of the liquid or the volume of the submerged part of the body. At the same time, the Archimedean force acting on the body also changes. Do you think there is any connection between gravity and the Archimedean force for floating bodies?

Teacher:(Group 6) Let's return to the table of substance densities again. Let us explain why an oil film forms on water.

So, the problem is solved, which means Liquids, like solids, are subject to the conditions of floating of bodies.

Let's continue the conversation about liquids.

One shallow vessel invited three immiscible liquids of different densities to visit at once and invited them to settle down with all the comforts. How were the liquids arranged in the hospitable vessel, if they were: machine oil, honey and gasoline.

Indicate the order in which the liquids are arranged.

Students:(Group 3) We immersed two test tubes with sand in water - one lighter, the other heavier - and both of them floated in the water. We have determined that the Archimedean force in both cases is approximately equal to the force of gravity.

Teacher: Well done. This means that if a body floats, then F A = F heavy. (I write on the board). What if the body sinks in liquid?

Students: Then the force of gravity is greater than the Archimedean force.

Teacher: What if the body floats?

Students: This means that Archimedean force is greater than gravity.

Teacher: So, we have obtained the condition for the floating of bodies. But it is not related to the density of the body or the density of the liquid itself. (This dependence was examined by the children of group 1). This means that the conditions of bodies can be formulated in two ways: by comparing the Archimedean force and the force of gravity or by comparing the densities of the liquid and the substance in it. Where in technology are these conditions taken into account?

Students: When building ships. Previously, wooden ships and boats were made. The density of wood is less than the density of water, and ships floated in water.

Teacher: Metal ships also float, but pieces of steel sink in water.

Students: They are treated as we did with plasticine: the volume is increased, the Archimedean force becomes greater, and they float. They also make pontoons and submarines.

Teacher: So, shipbuilding uses the fact that by changing the volume it is possible to impart buoyancy to almost any body. Is the connection between the floating conditions of bodies and changes in liquid density taken into account?

Students: Yes, when moving from sea to river, the draft depth of ships changes.

Teacher: Give examples of using the conditions of floating bodies in technology.

Students: Pontoons are used for river crossings. Submarines sail in the seas and oceans. For scuba diving, part of their tank is filled with water, and for surface diving, the water is pumped out.

(I show drawings of modern ships.)

Teacher: Take a close look at the nuclear icebreaker. There are several such icebreakers operating in our country. They are the most powerful in the world and can sail without entering ports for more than a year. But we'll talk more about this in the next lesson.

Board design: Homework § 48.

Lesson topic: Sailing conditions for bodies.

Lesson summary:

Together with the guys, we draw a conclusion about the research carried out. Once again we summarize the conditions for floating bodies using the table presented on the board.

I enjoyed my lesson today...
I want to …
I found out …
Today I am myself...

Sailing conditions

Purpose of the lesson: to clarify the conditions for the floating of bodies depending on the density of matter and liquid.

Educational:

familiarization of students with concepts: the condition of floating bodies

formation of a holistic perception of the scientific picture of the world

Educational:

development of students' operational thinking style;

development of students’ synthetic thinking;

development of skill and skill in conducting experiments;

continuation of work on the development of intellectual skills: highlighting the main thing, analysis, ability to draw conclusions, specification;

Educators:

developing students' interest in studying physics;

nurturing accuracy, ability and skill in rational use of one’s time, planning one’s activities.

Equipment for the lesson:

Test tube with stopper, potato ball, plasticine, water, saturated salt solution, vessel, dynamometer, scales with weights

1. Introduction. Updating knowledge.

Today a student in your class will start the lesson. So let's listen carefully

The blue whale's tongue weighs 3 tons, its liver weighs 1 ton, its heart weighs 600-700 kg, its blood weighs 10 tons, the diameter of its dorsal artery is 40 cm, and its stomach contains 1-2 tons of food; whale's mouth - room with an area of 24 m2. IN thrown ashore, dies almost instantly.

An interesting plant lives in the Pacific Ocean - this is macrocystis. Its length reaches 57 meters and its weight is 100 kilograms. This algae is called bladderwrack. Near each leaf blade there is a bubble the size of a large apple. The shell is thick, you won’t puncture it! It is inflated tightly, tightly with some kind of gas that the algae itself produces. This plant is very useful.

L hogs and ducks, heavy and clumsy on the shore, But so light and graceful in the water.

G a ship made of iron sinks, but a ship made of iron floats

2. Formulate the topic of the lesson???

Sailing conditions

Lesson objectives:

Learn to derive formulas for the floating conditions of bodies.

Learn to work with instruments, observe, analyze and compare experimental results, and draw conclusions.

Find out the condition under which a body sinks in a liquid, and the condition for the floating of bodies completely immersed in a liquid.

3.Experience:

– I have in my hands several blocks and balls of the same volume. Will the buoyancy forces of these bodies be the same when they are immersed in water? (same)

- Let's try to put them in the water. What do we see? Some bodies drowned, others floated. Why? What else did we not take into account when we talked about immersing bodies in liquid?

Conclusion from experience:

This means whether a body sinks or not depends not only on the force of Archimedes, but also on the force of gravity.

4. Let's repeat the material from the previous lesson

What force is called Archimedean force?

On what quantities does it depend?

What formula is used to calculate it?

How else can you determine buoyancy force?

In what units is it measured?

How is the Archimedean force directed?

How to determine gravity

What is the direction of gravity?

What is the resultant force?

How is the resultant of two forces directed along one straight line in one direction found? In different directions?

How will a body behave under the influence of two equal but oppositely directed forces?

5. Presentation of new material. Primary consolidation.

Let's look at different situations

(Ft >FA) (Ft =FA) (Ft< FА)

Let's make assumptions (hypothesis)

if the force of gravity is greater than the force of Archimedes (Ft > FA) -- The body sinks

if the force of gravity is equal to the force of Archimedes (Ft = FA) – The body floats,

if the force of gravity is less than the force of Archimedes (Ft< FА) ---Тело всплывает

The assumption must be tested experimentally.

Before you are various bodies and devices.

What materials should be used to prove our assumptions?

(dynamometer, liquid, body)

What measurements to make (determine the Archimedes force and the force of gravity and compare them with each other) or calculate using formulas.

Fill out the table

A= ρ andV g =

F t = mg =

conclusion (the ratio of gravity and Archimedean force determines the ability of the body: to swim, sink or float)

The ratio of gravity and Archimedean force determines the body’s ability to swim, sink or float.

Demonstrations: 1. A test tube body floats in water. 2. A potato ball sinks in water. 3. The same potato ball floats in salt water. 4. A plasticine ball sinks in water 5. A plasticine boat floats in water

In order for a body to float, it is necessary that the force of gravity acting on it be balanced by the Archimedean (buoyant) force.

F t = F a (1)

Archimedean force: F a = ρ f V f g (2)

Gravity: F t = mg = ρVg (3)

Let's substitute expressions (2) and (3) into equality (1): ρVg = ρ f V f g

Dividing both sides of this equality by g, we obtain the condition for the floating of bodies in a new form:

ρV = ρ f V f

For a body to float, partially protruding above the surface of the liquid, the density of the body must be less than the density of the liquid. When the density of the body is greater than the density of the liquid, the body sinks, because the force of gravity exceeds the Archimedean force.

Analysis of the exercise:

– What substances (ice, stearin, wax, rubber, brick) will float in water, milk, mercury?

– Using the table, determine which metals sink in mercury? (osmium, iridium, platinum, gold)

– What substances will float in kerosene? (cork, pine, oak)

4. Application of floating conditions for bodies

A) Sailing ships

- And now we must explain why a steel nail sinks, but a ship made of steel floats?

- Let's take plasticine. If you put it in water, it drowns. How to make sure he doesn't drown?

B) Swimming of fish and whales

How can fish and whales change their diving depth? (fish due to a change in the volume of the swim bladder, whales due to a change in the volume of the lungs, which means due to the force of Archimedes)

The density of living organisms inhabiting the aquatic environment differs very little from the density of water, so their weight is almost completely balanced by the Archimedean force. A fish can change the volume of its body by compressing its swim bladder with the efforts of its pectoral and abdominal muscles, thereby changing the average density of its body, thanks to which it can regulate the depth of its dive.

The swim bladder of a fish easily changes its volume. When a fish, with the help of muscles, descends to a greater depth and the water pressure on it increases, the bubble contracts, the volume of the fish’s body decreases and it swims in the depths. When rising, the swim bladder and volume of the fish increases and it floats to the surface. This is how the fish regulates the depth of its dive. Swim bladder of a fish This is interesting

Whales regulate their dive depth by increasing and decreasing their lung capacity. This is interesting

The average density of living organisms inhabiting the aquatic environment differs little from the density of water, so their weight is almost completely balanced by the Archimedean force. Thanks to this, aquatic animals do not need strong and massive skeletons. For the same reason, the trunks of aquatic plants are elastic.

Birds have a thick, water-impervious layer of feathers and down, which contains a significant amount of air, due to which the average density of their body is very low, so ducks do not submerge much in the water when swimming.

B) Submarine navigation

– How can submarines rise and fall to different depths? (due to changes in its mass, and therefore gravity)

D) Human swimming in fresh water and salt water

The average density of the human body is 1030 kg/m. Will a person swim or drown in the river and in the salt lake?

Floating bodies

203. A swimmer lying motionless on his back on the water takes a deep breath and exhales. How does the position of the swimmer’s body change in relation to the surface of the water? Why?

204. Are the buoyancy forces acting on the same wooden block floating first in water and then in kerosene the same?

205. Why does a plate placed flat on the surface of the water float, but one placed edge-on into the water sinks?

206. Can a lifebuoy hold any number of people who grab onto it?

207. Heavy lead plates are placed on the chest and back of the diver, and lead soles are attached to the shoes. Why do they do this?

208. A piece of wood is lowered into a vessel with water. Will this change the pressure at the bottom of the vessel if water does not pour out of the vessel?

209. A glass is filled to the brim with water. A piece of wood is placed in it so that it floats freely. Will the weight of the glass change if water still fills it to the brim?

Answers:203. When inhaling, the swimmer floats up, and when exhaling, he plunges deeper into the water, since when breathing, the volume of the chest changes and the Archimedean force changes accordingly.

(When inhaling, the swimmer floats up, when exhaling, he plunges deeper into the water, since during breathing the volume of the chest changes, but the body weight remains almost constant. Therefore, the total volume of the body increases when inhaling, decreases when exhaling, and the volume of the part of the body immersed in water does not change.)

204. Same. The block floats in both fluids, which means that the buoyant force in each of them is equal to the force of gravity acting on it.

206. No, since the lifting force (the difference between the maximum Archimedean force and the force of gravity) of a circle has a limited value.

207. To increase the force of gravity and make it greater than the Archimedean force, otherwise the diver will not dive to the required depth.

208. The pressure will increase as the water level in the vessel rises.

209. It will not change, since the weight of a piece of wood is equal to the weight of the water displaced by it (and poured out of the glass).

6. Experimental task.

Determine body weight:m=

DefineFt according to the formula and using a dynamometer, fill out the table.

Define FAUsing the formula and using a dynamometer, fill out the table.

Formulate a conclusion (the ratio of gravity and Archimedean force determines the ability of the body: to swim, sink or float)

Fill out the table

A= ρ andV g =

F t = mg =

conclusion(based on experiment)

conclusion (in fact)

F t =

7. Homework:

8.Conclusion: with Now our lesson time is coming to an end. And although we have not solved all the problems, our journey along the roads of physics does not end!

Floating is the ability of the body to stay on the surface of a liquid or at a certain level inside a liquid.

We know that any body in a liquid is acted upon by two forces directed in opposite directions: gravity and Archimedean force.

The force of gravity is equal to the weight of the body and is directed downward, while the Archimedean force depends on the density of the liquid and is directed upward. How does physics explain the floating of bodies, and what are the conditions for floating bodies on the surface and in the water column?

Archimedean force is expressed by the formula:

Fout = g*m f = g* ρ f * V f = P f,

where m is the mass of the liquid,

and Pf is the weight of the fluid displaced by the body.

And since our mass is equal to: m f = ρ f * V f, then from the formula of the Archimedean force we see that it does not depend on the density of the immersed body, but only on the volume and density of the fluid displaced by the body.

Archimedean force is a vector quantity. The reason for the existence of the buoyant force is the difference in pressure on the upper and lower parts of the body. The pressure indicated in the figure is P 2 > P 1 due to the greater depth. For the Archimedes force to arise, it is enough that the body is at least partially immersed in the liquid.

So, if a body floats on the surface of a liquid, then the buoyant force acting on the part of this body immersed in the liquid is equal to the gravitational force of the entire body. (Fa = P)

If the force of gravity is less than the Archimedean force (Fa > P), then the body will rise from the liquid, that is, float.

In the case when the weight of the body is greater than the Archimedean force pushing it out (Fa

From the obtained ratio, important conclusions can be drawn:

The buoyancy force depends on the density of the liquid. Whether a body sinks or floats in a liquid depends on the density of the body.

A body floats when completely immersed in a liquid if the density of the body is equal to the density of the liquid

A body floats, partially protruding above the surface of the liquid, if the density of the body is less than the density of the liquid

- if the density of the body is greater than the density of the liquid, swimming is impossible.

Fishermen's boats are made of dry wood, the density of which is less than that of water.

Why do ships float?

The hull of a ship that is immersed in water is made voluminous, and inside this ship has large cavities filled with air, which greatly reduce the overall density of the ship. The volume of water displaced by the ship is thus greatly increased, increasing its buoyancy force, and the total density of the ship is made less than the density of water, so that the ship can float on the surface. Therefore, each ship has a certain limit on the mass of cargo that it can carry. This is called the ship's displacement.

Lesson developments (lesson notes)

Line UMK A.V. Peryshkin. Physics (7-9)

Attention! The site administration is not responsible for the content of methodological developments, as well as for the compliance of the development with the Federal State Educational Standard.

Lesson topic: Sailing conditions tel.

Lesson objectives:

Educational: teach to analyze, highlight (main, essential),
bring you closer to solving problem situations on your own.
Developmental: develop interest in specific activities in the lesson,
develop the ability to compare, classify, generalize facts and concepts.
Educational: create an atmosphere of collective search, emotional elation, joy of learning, joy of overcoming difficulties.

Place of the lesson in the section:"Pressure of solids, liquids and gases", after studying the topic "Pressure of liquids and gases on a body immersed in them. Archimedean force."

Lesson type: Lesson on reviewing subject knowledge.

Basic terms and concepts: mass, volume, density of matter, body weight, gravity, Archimedean force.

Interdisciplinary connections: mathematics

Visibility: demonstration of the behavior of different bodies immersed in water; body floating conditions depending on density.

Equipment:

a) for demonstration

a plastic jar with water, three objects on a string: an aluminum cylinder, a plastic ball, a hermetically sealed bottle of water (prepared in advance by the teacher), which can be in equilibrium anywhere in the liquid;
a bath of water, a plate of aluminum foil, pliers.

b) for frontal work

Scales with weights, measuring cylinder (beaker), float capsule with a lid (3 each), dry sand, threads, filter paper, electrical tape, instructions for completing frontal experiment tasks, notebooks for laboratory work.

Forms of work in the lesson: frontal in pairs, individual.

Organizing time;
Initial check of understanding of previously studied material;
Practical work to verify the findings;
Reflection;
Homework.

Today in the lesson we will continue to study the behavior of bodies immersed in water. Let's look at a few experiments; you will carry out some of the experiments yourself and perform some calculations.

We lower an aluminum cylinder, a ball and a bottle of water into the water in succession. We observe the behavior of bodies.

Result: the cylinder sinks, the ball floats up, the bubble floats, completely immersed in water.

Problem situation: Why? – (Ratio of forces acting on the body).

– All bodies in water are acted upon by two forces: the force of gravity, directed downward, and the buoyant force (Archimedes’ force), directed upward.

– From the rule of addition of forces acting on a body along one straight line, it follows: sinks if F t ˃ F A; floats up if F t ˂ F A; floats if F t = F A.

Let's do an experiment and check the relationship between gravity and buoyant force. (The laboratory work “Elucidation of the conditions for floating bodies in a liquid” is taken as a basis - page 211 of the textbook).

Fill the capsule 1/4 full with sand, determine its mass in grams on the scale. Convert the mass value into kg and write it in the table.
Place the capsule in water and determine the volume of displaced water in cm3. To do this, mark the water levels in the beaker before and after immersing the capsule in water. Record the volume value in m3 in the table.

P = F heavy = mg And F A = ρ f gV t

Fill the capsule completely with sand and determine its mass in grams on the scale. Convert the mass value into kg and write it in the table.
Place the capsule in water and determine the volume of displaced water in cm3. To do this, mark the water levels in the beaker before and after immersing the capsule in water. Write the volume value in m 3 in the table.
Calculate gravity and Archimedean force using the formulas:

P = F heavy = mg And F A = ρ f gV

Compare Archimedean force with gravity. Enter the calculation results in the table and note: the capsule sinks or floats.

Determine at what ratio of gravity and Archimedean force the capsule will float anywhere in the liquid, completely immersed in it? What value will the volume of water displaced by the capsule have?
Determine the mass for the floating body (without calculation).
Fill the capsule with sand to the required mass, then lower it into the water and verify from experience that your reasoning is correct.
Draw a conclusion about the condition for a body to float in a liquid.

Let's check the floating conditions depending on the density of the substance from which the bodies are made and the density of the liquid. For this we have a bath of water, a plate of aluminum foil, and pliers.

By bending the corners, we will make a box from the plate. Let's lower it to the surface of the water. We observe the box floating on the surface of the water.
Let's take the box out of the water and return the plate to its flat appearance. fold the plate in half, in four, etc. Using pliers, squeeze the foil and lower it into the water.

Result: the box-shaped plate floats, but when compressed it sinks.

Problem situation: Why? – (Ratio of body and water densities).

density boxes made of aluminum foil is less dense than water, and the density of a compressed lump of foil is greater than the density of water.
Conditions for floating bodies: sinks if ρ t ˃ ρ water; floats up if ρ t ˂ ρ water; floats if ρ t = ρ water. (ρ aluminum = 2700 kg/m3; ρ water = 1000 kg/m3).

Experience 3. Look and explain the operation of the device made by the student according to the assignment for §52 (p. 55 of the textbook). "Cartesian Diver". Instead of a clear bottle, the student used a regular pipette.

The device allows you to demonstrate the laws of floating of bodies.

§52; exercise 27(3,5,6).

Body mass,
m, kg

Gravity,
F heavy, N

Volume of displaced water,
V, m 3

Archimedes' power
F A, N

Comparison F cord and F A

Behavior of the capsule in water

The topic of the 7th grade physics lesson is “Conditions for floating bodies.” There are 20 students in the class. The majority of them have good mathematical training. The guys are inquisitive and active. They work well in a team. Participate in preparing equipment for the lesson.

The purpose of the lesson: to interest students, to bring them closer to independently solving problem situations. During the lesson, children learn to independently plan ways to achieve goals, including alternative ones, and consciously choose the most effective ways to solve a problem.

The type of lesson - a lesson on repeating subject knowledge - allows you to test the knowledge acquired in the previous lesson and prepare for solving problems on the topic in the next lesson.

The selected stages of the lesson are logically connected with each other, there is a smooth transition from one to another. During the lesson, the teacher only guides and corrects the actions of the students, who work independently for almost the entire lesson. To save time when completing the practical part, during additional classes, students prepared two capsules with sand, fully and partially filled (tasks 1 and 2), the third remained empty. During the lesson, the children learned to draw conclusions from the experiment and actively discussed solutions to problem situations. At the final stage, the children’s attention was once again focused on the topic of the lesson. The teacher commented on the homework and gave grades for oral answers; after the lesson, the notebooks for laboratory work were checked.

I believe that the goals of the lesson were achieved: the children learned to analyze, highlight (the main, essential), compare, classify, generalize facts and concepts, and find solutions to problem situations. The lesson created an atmosphere of collective search, emotional elation, the joy of learning, and the joy of overcoming difficulties.