Laboratory work 7 measurement of buoyancy force. Laboratory work "determining the magnitude of the buoyant force acting on a body immersed in a liquid"

Topic: Laboratory work "Determination of the buoyant force acting on a body immersed in a liquid".

Goals:

learn to measure the buoyant force acting on a body immersed in a liquid;

develop the skills of independent individual work, the ability to compare, observe, draw conclusions;

develop an interest in the subject

During the classes:

1. Organizing moment. goal setting

2. Actualization of basic knowledge

3. Performing laboratory work with a computer model.

4. The results of the lesson.

5. Homework.

Teacher: Hello,our great compatriot M.V. Lomonosov said: "I put one experience higher than a thousand opinions born only of the imagination." Today we will try ourselves not just in the role of a student, but in the role of a scientific researcher. Where does any research begin? Of course, from the experiment.

But, first, let's recall the material covered.

Teacher questions:

Student Answers:

– What forces act on a body immersed in a liquid?

F T , F BUT

– What force is called buoyant force?

The force generated when a body is immersed in a liquid or gas

– Where F is directed T ?

Down

– Where F is directed BUT ?

Up

– Name the formula F BUT , characterize the quantities included in it

F BUT .= wellV T g

How to determine the weight of a body immersed in a liquid?

P = F T –F BUT

Teacher:

If the body is thrown into the water

Or just drop

There will be the power of Archimedes

Press down on him.

If the weight of water in volume

The submerged part to know

Can the force of Archimedes

3. That's what we're going to do in today's lesson.doing lab work using interactive th model .

Equipment: a computer,interactive model.

In order to get started, you need to determine the division price of the devices with which you will work todayusinginteractive model. Let's remember the rule.

Student:

find the two nearest strokes of the scale, near which the magnitude values ​​are written;

subtract the smaller value from the larger value and divide the resulting number by the number of divisions in between.

C =- the price of division of the scale of the device

Experience 1.

(Description in work) Fill in table 1

Table 1.

№ experience

P, body weight in air (H)

R 1 , body weight in water (H)

F Arch

F Arch= P - P 1

1.aluminum cylinder

2. copper cylinder

part 2

Experience 2 .

1. Measure the volume of water poured into the beaker (Vo).

2. Measure it after immersing the cylinders there (V b, V m).

3. CalculateV body =V-Vo. (Convert V to m 3 , knowing that 1ml = 1cm 3 =0.000001m 3)

4.CalculateF Arch \u003d P liquid \u003d Mzh * g \u003d ρ well gV (ρ f= 1000 kgm 3)

Fill in table 2

Table 2.

№ experience

Vo, volume of poured water,

(cm 3 )

V, water volume

3 )

V t, body volume, cm 3

V t, volume

body, m 3

F Arch

1.cylinder big

2.cylinder small

On the basis of the experiments performed, conclude

Conclusion:

1. Archimedean force, does not depend on the density of the substance from which the body is made

2. The force acting on a body immersed in a liquid is directly proportional to the volume of the body

Reflection

Finish the sentence:

Today in class I learned…………..

It was interesting to know…………..

It was difficult……………

5.D/z

§ 48, 49 ex. 24 (1, 2)

Experience 1. Study of the dependence of the buoyancy force on the density of the body

Table 1.

№ experience

P, body weight in air (H)

R 1 , body weight in water (H)

F Arch

F Arch= P - P 1

1.aluminum cylinder

2. copper cylinder

100

Experience 2. Investigation of the dependence of the buoyancy force on the volume of the submerged body.

Table 2.

№ experience

Vo, volume of poured water,

(cm 3 )

V, water volume

after the body is immersed in it, (see 3 )

V t, body volume, cm 3

V t, volume

body, m 3

F Arch

1.cylinder big

100

137

0,000037

2.cylinder small

100

113

0,000013

Laboratory work 7 Determination of the buoyant force acting on a body immersed in a liquid. The purpose of the work: to experimentally detect the buoyant effect of a fluid on a body immersed in it and determine the magnitude of the buoyant force. Instruments and materials: a dynamometer, a tripod with a clutch and a foot, two bodies of different volumes, glasses with water and a saturated solution of salt in water.

Training tasks and questions 1. Use vectors to show the forces acting on the body in the 1st and 2nd cases. 2. Where is it easier to hold the body: in air or in water? __________ ___________________________________ Why? _____________ _______________________________

3. Write down the formulas: Archimedean force Body weight 4. Write down the formula for finding the Archimedean force, if you know the weight of the body in air - R 1 and in water - R 1 f. F A \u003d _____________ 5. Body weight in air P 1 \u003d 120N Body weight in water R 1 w \u003d 100 N Archimedean force F A \u003d ____________ N

Workflow 1. Mount the dynamometer on a tripod and hang the first body on a thread. Note and record the dynamometer reading in the table. This will be the weight of the body in the air - R 1 2. Substitute a glass of water and release the clutch with the foot and dynamometer until the whole body refuses under water. Note and record the dynamometer reading in the table. This will be the weight of the body in water - R 1 f. 3. Based on the data obtained, calculate the buoyancy force acting on the first body: F 1 \u003d P 1 - P 1 w \u003d __________ 4. Instead of pure water, take a saturated salt solution and again determine all this body in a salt solution - R 1 w, Write in table and determine the buoyancy force F 1

5. Suspend a body of a different volume from the dynamometer and determine in the same way as for the first body, buoyant force in water and in a saturated salt solution-F 2. Body weight in air, N Body weight in liquid, N Buoyancy force, N R 1 R 2 R 1 F R 2 F F ​​1 F 2 Water Satur. salt solution in water Record the result in the table. Conclusion: ____________________________ _______________________

Lab 1

Determination of the buoyant force acting on a body immersed in a liquid

Objective: study of the parameters on which the Archimedes force acting on a body immersed in a liquid depends.

Introduction

A body immersed in a liquid or gas is subjected to a buoyant force (Archimedean force). According to the law of Archimedes, the buoyant force F A is directed vertically upwards and is numerically equal to the weight of the liquid (or gas) displaced by the body. Mathematically, Archimedes' law is expressed by the formula

F A =  gV,

where  is the density of the liquid; g- acceleration of gravity; V - the volume of the part of the body immersed in a liquid (or gas). In a state of weightlessness, the Archimedean force does not act.

Due to the buoyant force, the weight of any body in the liquid is less than in air. If the weight of the body in the air R 1 , and in liquid R 2 , then the value of the Archimedean force acting on this body when it is immersed in a liquid can be found as the difference R 1 and R 2 , i.e.

F A = R 2 – R 1 .

Description of the experiment

In this work, you are invited to measure the buoyancy force acting on a body immersed in a liquid, and also to investigate the dependence of the buoyancy force on the volume of the body and on its mass.

The measurement of the Archimedean force will be carried out using a force sensor: first, the body will be weighed in air and in liquid, and then the difference between the obtained values ​​will be calculated.

Equipment and materials

Tasks

1. Measure the weight of bodies in air and water.

2. Determine the buoyancy force acting on bodies immersed in water.

3. Investigate the dependence of the buoyancy force on the volume of the body.

4. Investigate the dependence of the buoyancy force on the volume of the submerged part of the body.

5. Investigate the dependence of the buoyancy force on the body mass.

6. Analyze the received data.

7. Draw conclusions.

Running an experiment

1. Familiarize yourself with the general safety rules for practical work in the physics classroom.

2. Before starting work, you need to check the connection and operation of the force sensor. Connect the sensor to the UIOD. Select from the menu File paragraph New. The sensor should be detected automatically, then on the device screen you will see the image shown in Figure 1.

3. To conduct an experiment, you must change Frequency sensor measurements at 1 Hz and Experiment time for 10 s.

Ipart: checking the dependence of the buoyancy force on the volume of the body

1. Suspend your body from the force sensor. Next, determine the weight of the body in the air and enter the results of weighing and the average value of the weight in the table. Measure the weight value several times (3-5).

2. Then place a beaker of water under the body and immerse the entire body in the water as shown in Figure 2. While doing this, you must monitor the readings of the force sensor. Body weight in water must also be determined 3-5 times. Thus, you will determine the weight of the body in water and enter the results of weighing and the average weight in the table.

3. Then calculate and enter in the table the value of the buoyancy force acting on the body. For calculation, use the average values ​​of body weight in air and in water.

4. Follow steps. 1-3 with a body of a different volume.

You must also record the results of repeated weighing of this body in the report table.

IIpart: checking the dependence of the buoyancy force on the volume of the submerged part of the body

1. Hang a metal cylinder from a set of bodies of different masses and the same volume to the force sensor.

2. Weigh the cylinder in the air and enter the value in the table. In this part of the work, due to the limited time of the lesson, we recommend conducting single weight measurements.

3. Next, you must draw lines that conditionally mark the division of the cylinder into four equal parts. It is convenient to draw these lines on the side surface of the cylinder with a colored pencil in a contrasting color. We recommend that you first measure half the height of the cylinder and draw a line, then divide each half in half again. Thus, the cylinder will have clearly marked lines on its side, conditionally dividing it into four parts.

4. Then you must immerse first ¼, then ½, ¾ of the volume of the cylinder into the liquid, then immerse it in its entirety and weigh in each case. For each value of the volume of the part of the cylinder immersed in water, you must determine the weight of the body in water and enter this value in the table.

5. Calculate and enter in the table the values ​​of the buoyancy force acting on the body in each case.

IIIpart: checking the dependence of the buoyancy force on the mass of the body

1. Determine the weight in air and in water for two cylinders from a set of bodies of different masses and the same volume when they are completely immersed in water and enter the data in the table. Take measurements several times (3-5).

2. Calculate and enter in the table the values ​​of the buoyancy forces acting on the cylinders. Analyze the received data and answer the control questions.

3. Make a detailed conclusion after completing the laboratory work. We remind you that the conclusion must be drawn based on the goals of the work and the tasks set in it.

Processing the results of the experiment

I. Fill in the table for the first part of the work.

Table 1. Results of measurements of the weight of bodies of various volumes when weighed in air and in water

II. Complete the table for the second part of the work.

Table 2. Results of measurements of body weight depending on the part of the volume of the body immersed in water. Body weight when weighed in air R 1 =…., N

III. Complete the table for the third part of the work.

Table 3. Results of weighing bodies of different masses, but the same volume

test questions

1. Does the buoyancy force acting on a body immersed in a liquid depend on its volume?

2. Are the buoyant forces acting on a block floating first in water and then in kerosene the same?

3. What decreases when a body is immersed in a liquid - body weight or gravity?

4. A piece of ice floats in a glass filled to the brim with water. Will the water overflow if the ice melts?

Additional tasks.

1. Calculate the value of the Archimedes force of choice for the first part or for the third part of the experiment, taking into account the errors. When calculating errors, consider the instrumental relative error of the force sensor equal to δ R = 3%.

2.Suggest a method for determining the volume of the cavity inside the body. Consider that the density of the material from which the body is made is known.

3. Carry out work to study the dependence of body weight on the density of the liquid in which it is immersed. To do this, immerse bodies of different weights, but having the same volume, in salt water. Compare the results obtained with the results obtained when bodies are immersed in pure water.

4. Check by experience whether the buoyancy force depends on the depth of the body's immersion in the liquid .

Laboratory work №8.

Subject: Determination of the buoyant force acting on a body immersed in a liquid.

Why egg

pops up?

Target: To study the effect of a liquid on a submerged body, to experimentally investigate the dependence of the buoyancy force on the density of the liquid and the volume of the body.

Lesson objectives:

• 1. To teach students to detect the presence of a force pushing a body out of a liquid, to find out on what factors the magnitude of the buoyancy force depends (does not depend) and to formulate the law of Archimedes by establishing the dependence of the Archimedes force on the volume of the body immersed in the liquid and on the density of the liquid.
• 2. To cultivate the ability to work purposefully to achieve joint and personal goals, to cultivate tolerance and respect for other opinions, to cultivate sociability.
• 3. Develop techniques for enhancing mental activity - analysis, synthesis, comparison, generalization and abstraction.

1. Where is the buoyant force directed?

2. Does body weight change when immersed in water?

3. Body weight?

Target: to discover experimentally the buoyant action of a liquid on a body immersed in it.

Equipment:

tripod with clutch, dynamometer, 2 bodies, glasses with clean and salt water.

Working process.

1. To calculate the buoyancy force, you need to measure ...

1. To calculate the buoyancy force, you need

1) measure body weight in air F 1 .

2) measure body weight in water F 2 .

Where is the weight more?

2. To calculate the pushing force, you need ...

F you are t = F 1 -F 2 .

Reporting table .

Body weight in air F 1 ,

Water

Body weight in water F 2 ,

Pure

buoyant force,

salty

F you are t = F 1 -F 2 . (H)

• In order to calculate the buoyancy force...

subtract the smaller weight from the larger one, i.e.

F you are t = F 1 -F 2 .

Conclusion: (What did you measure? What did you calculate? What determines the buoyancy force?)

Additional task: to investigate the dependence of the buoyancy force on the volume of the body.

• We work with only one liquid.

Reporting table .

Body weight in air F 1 ,

Body

Body weight in water F 2 ,

big

buoyant force,

small

F you are t = F 1 -F 2 . (H)

Conclusion: (What determines the pushing force?)

D/Z: & 50-51-retelling, questions orally

• Well done!
• Thank you for the lesson.

Additional research.

Investigate whether the buoyancy force depends on:

• body density;
• body shape;
• diving depth.

LABORATORY WORK.

DEFINITION OF THE PUSHING FORCE.

Goals : to discover experimentally the buoyant effect of a fluid on a body immersed in it and determine the buoyant force.

Devices and materials : a dynamometer, a tripod with a clutch and a foot, two bodies of different volumes, glasses with water and a saturated solution of salt in water.

Instructions for work:

1. According to the law of Archimedes, a buoyant force acts on a body immersed in a liquidF A, equal to the weight mgdisplaced fluid:

F A = mg. (1)

To compare the Archimedean force with body weight, you need to measure the body weightPusing a dynamometer and calculate the Archimedean forceF A . Archimedean forceF A is determined by the formula:

F A = mg =  Vg (2),

where  - density of water ( \u003d 1000 kg / m 3), V- the volume of water displaced by the body,g- acceleration of gravity (g\u003d 9.81 m / s 2).

Volume VThe displaced water can be measured using a measuring cylinder as the difference in the water level when the body being examined is immersed in it and without the body.

Archimedean force FA, acting on a body sinking in water, can be found by measuring the body weight with a dynamometerPin the air and strengthP 1 that keeps the body in balance when it is immersed in water:

P=F A + P 1 , F A = P - P 1 .

2. Measure the weight P of the first body using a dynamometer.

3. Measure the strength P 1 acting on the hook of the dynamometer when the body is completely immersed in water. To do this, fix the dynamometer on a tripod and hang a weight from it. Place a glass of water and lower the clutch with the foot and dynamometer until the entire body is under water. This will be the weight of the body in water.

4. Calculate the buoyant force acting on the body.

5
. Instead of pure water, take a saturated salt solution and calculate the buoyant force.

6. Suspend another body from the dynamometer and do step 2 - step 5

7. Record the results of measurements and calculations in the reporting table.

body weight in air

body weight in liquid

Buoyancy force

F, N F \u003d P -P 1

R ’

P''

P 1 ’

P 1 ’’

F'

F''

Water

Saturated salt solution in water

Draw conclusions based on the experiments performed.

Test questions.

1. In what water and why is it easier to swim: in the sea or river?

2. A steel bar suspended on a thread is immersed in water. Name the interacting bodies and the forces acting on the block. Depict these forces graphically.

3. The volume of a piece of iron is 0.1 m 3 . What buoyant force will act on it when completely immersed in kerosene?