I. A. Izyumov,
, MOU gymnasium No. 3, Aksai, Rostov region

Measuring the efficiency of an inclined plane

Impossible direct hit experiment
into a narrowly defined theoretical target.

Imre Lakatos

When theory matches experiment,
It is no longer an opening, but a closing.

Pyotr Leonidovich Kapitsa

The purpose of the lesson: development of skills to independently apply knowledge, to carry out their transfer to new conditions.

Didactic task: ensuring the assimilation of new knowledge and methods of action at the level of application in various situations.

Reflective activity of the student: self-affirmation, self-realization and self-regulation.

D The activity of the teacher to ensure reflection: presentation of educational material, taking into account the zone of the closest and actual development of the student.

Indicators of the real result of solving the problem: independent performance of tasks using knowledge in various situations.

The logic of building a lesson: actualization of the complex of knowledge → application of knowledge in various situations → control and self-control.

Equipment: wooden board, wooden block, dynamometer, measuring ruler.

During the classes

I. Updating the knowledge complex(15 minutes)

Reference drawing on the board. The teacher together with the students solves the problem:

What work must be done in order to drag a load along a plane with an inclination of 30 ° to a height of 2 m, applying a force that coincides in direction with the displacement? The mass of the load is 400 kg, the coefficient of friction is 0.3. What is the efficiency of this?

Solution

II. Problem solving(30 min)

1 (10 min). The teacher works with the class to:

Place a small object (elastic band, coin, etc.) on the ruler. Gradually raise the end of the ruler until the object begins to slide. Measure your height h and base b obtained inclined plane and calculate the coefficient of friction.

Solution. F T x = F tr x ; mg sinα = μ F t cosα; μ = tanα = h/b.

Having received the calculation formula, students, using a wooden board, a wooden block and a ruler, experimentally determine the coefficient of friction themselves and write down the result in workbooks.

2 (10 min). The teacher works with the class to:

Find the efficiency of an inclined plane with a length of 1 m and a height of 0.6 m, if the coefficient of friction when a body moves along it is 0.1.

Solution. Using the second result of solving the problem , we obtain:

The teacher proposes to measure the length of a wooden board and determine the efficiency of the inclined plane for the height and coefficient of friction obtained by solving the problem. The result is recorded in a notebook.

3 (10 min). The teacher proposes to determine the efficiency of the inclined plane for the height value obtained when solving the problem in another way, and then compare the results and draw conclusions.

Lay the block on an inclined plane; attaching a dynamometer to it, evenly pull it up along the inclined plane; measure traction force F .

Measure gravity with a dynamometer F t acting on the bar, and find the experimental value of the efficiency of the inclined plane:

Homework. Calculate the maximum possible value of the gain in force obtained for a given slope of the plane: kmax = l/h.

Find experimentally the gain in force obtained with the help of an inclined plane: k uh = F T /F.

Compare your results. Draw your own conclusions.

Literature

1. Rymkevich A.P. Physics. Taskbook-10–11: A manual for general education. institutions. – M.: Bustard, 2004.
2. Dick Yu.I., Kabardin O.F., Orlov V.A., Kabardina S.I., Nikiforov G.G., Shefer N.I. Physical workshop for classes with ang. the study of physics: Didact. material: 9–11 cells: Ed. Yu.I. Dick, O.F. Kabardin. – M.: Enlightenment, 1993.

Laboratory work number 6.

Determining the efficiency of an inclined plane

Goal of the work:

1. calculate the efficiency of the proposed inclined plane and draw a conclusion about its value;

2. verify by experience that Ap< Аз.

Equipment: dynamometer, board, tripod, wooden block, measuring tape (or ruler), set of weights (fig.).

Progress:

1. Determine the division value of measuring instruments. Cd \u003d .... N. (dynamometer)

Cl = .... N. (rulers).

2. Using a dynamometer, determine the weight of the bar (R), lifting it up h(write in the table).

3. Moving the bar at a constant speed up the inclined plane, measure the traction force required for this (F). (write in table)

4. Use the ruler to define the path s passed by the lower edge of the load, and the height h on which it was raised. (write in table)

5. Determine the total weight of the bar with two weights (R), (write in the table).

6. Loading the bar with two weights and attaching a dynamometer to it, move the bar at a constant speed up the inclined plane. Measure the traction force required for this ( F). s And h the same. (to table)

7. Lower the plank below and repeat experiment 2. S the same , h measure (record in a table)

general task for 3 experiments:

8. Calculate useful and expended work: ,

9. Find the efficiency of the inclined plane.

10. Enter the results of the calculations in the table.

Conclusion: as a result of the work, we

physics teacher GOU lyceum No. 384 of the Kirovsky district of St. Petersburg

Introduction

The concept of "efficiency" is first introduced in the course of physics in the 7th grade. The use of modern educational technologies allows students to increase the motivation for learning and the efficiency of mastering the material.

During the lesson "Determining the efficiency when lifting the body on an inclined plane", the technology of research in training was used.

The lesson includes the following stages: updating knowledge, studying new material (performing laboratory work), conducting research, reflection.

During the lesson, work in pairs was used. The use of this technology allowed students not only to acquire new knowledge, but also to develop the ability for active creativity.

Goals and objectives of the lesson

Lesson objectives:

Updating students' knowledge

Generate interest in the material being studied

・Motivate students

Goals:

Tutorials:

· Introduce students to a new physical quantity - the efficiency of the mechanism.

Verify by experiment that the useful work done with the help of an inclined plane is less than the work expended.

Determine the efficiency when lifting a body on an inclined plane.

Find out what determines the efficiency when lifting a body-inclined plane.

· Check the ability to apply the acquired knowledge to solve practical and research problems.

Show the connection of the studied material with life.

Developing:

• To create conditions for the development of the personality of students in the course of their activities.
• To promote the development of practical skills and abilities.
• Form the ability to put forward a hypothesis, test it.
• To teach to highlight the main thing, to compare, to develop the ability to generalize, systematize the knowledge gained. Develop the ability to work in pairs.

Educational:

• Development of communication skills.
• Development of teamwork skills (mutual respect, mutual assistance and support).

Health saving:

Building a model of a health-saving lesson.

Lesson Form: Research work of students.

During the classes

· Organizing time.

· Updating knowledge. Warm up.

· Perform laboratory work.

· Physical pause.

· Research part of the work.

· Homework.

Consolidation of the studied material.

1. Organizational moment. Slides 2-3

2. Actualization of knowledge. Warm up. Slides 4-7

1. What are simple mechanisms?

List what simple mechanisms you know.

Give examples of the application of simple mechanisms.

What are they needed for?

Explain in your own words the meaning of the phrase “gain a gain in strength.”

Formulate the "golden rule" of mechanics.

2. Consider the situation. Slides 8 - 9

A worker needs to load a barrel of gasoline into the back of a truck. To just lift it, you need to apply a very large force - a force equal to the gravity (weight) of the barrel. The worker cannot apply such a force.

. What should he do?

(students make their own suggestions)

... then he puts two boards on the edge of the body and rolls the barrel along the formed inclined plane, applying a force much less than the weight of the barrel!

Conclusion: Slide 10 - 11

· An inclined plane is used to move heavy objects to a higher level without directly lifting them.

· Such devices include ramps, escalators, conventional stairs and conveyors.

3. What parameters characterize the inclined plane?

3. Laboratory work No. 10. Slides 12 - 21

"Determination of the coefficient of efficiency when lifting a body along an inclined plane."

Subject of study: inclined plane.

Compare useful and expended work.

Equipment:Computer, multimedia projector (for teachers)

· A set of cargoes

· Dynamometer

Measuring tape (ruler)

Learning new material.

1. Introduce students to a new physical quantity - the efficiency of the mechanism.

Efficiency is a physical quantity equal to the ratio of useful work to spent work, expressed as a percentage.

Efficiency is indicated by the letter "this"

Efficiency is measured as a percentage.

What work is useful, what work is expended?

Work expended Aexpended=F*s

Useful work Auseful = P*h

For example , efficiency = 75%.

This number shows that out of 100% (of work expended), useful work is 75%.

Job instruction.

Performing laboratory work.

Determine the price of division of instruments (dynamometer and ruler).

1. Install the board at height h, measure it.

2. Measure the weight of the bar P with a dynamometer.

3. Place the block on the board and use a dynamometer to pull it evenly up along the inclined plane. Measure the force F. Remember how to use the dynamometer correctly.

4. Measure the length of the inclined plane s.

5. Calculate useful and expended work.

6. Calculate the efficiency when lifting the body on an inclined plane.

7. Write down the data in table No. 1.

8. Draw a conclusion.

Registration of work results

Table 1.

Useful work _______________ than expended.

Efficiency when lifting a body along an inclined plane _____%, i.e. this number indicates that _______________________________________________________________.

4. Physical break. Slides 22 - 25

Inclined plane examples. Students watch slides with examples of the use of an inclined plane.

5. Research work. Slides 26 - 30

Problem. What influences the efficiency of an inclined plane?

Hypothesis. If you increase (decrease) the height of the inclined plane, then the efficiency when lifting the body along the inclined plane will not change (increase, decrease).

If you increase (decrease) the weight of the body, then the efficiency when lifting the body along an inclined plane will not change (increase, decrease).

Students choose one of the proposed research options:

from the height of the inclined plane?

How does the efficiency of lifting a body down an inclined plane depend? from body weight?

Registration of work results

Table 2.

The efficiency when lifting a body along an inclined plane depends (does not depend) on the height of the inclined plane. The greater (less) the height of the inclined plane, the more efficient __________.

The efficiency when lifting a body along an inclined plane depends (does not depend) on the weight of the body. The more (less) body weight, the more efficient __________.

Discussion of research options.

6. Homework. Slides 31 - 32

Paragraph 60, 61, task 474.

For those who wish to prepare messages.

Simple mechanisms in my house

Meat grinder device

Simple mechanisms in the country

Simple mechanisms in construction

Simple mechanisms and the human body

7. Consolidation of the studied material Slides 31 - 34
Work with text

When using _________________ mechanisms, a person commits _______________. Simple mechanisms allow you to win ______________. At the same time, how many times ________________ is in force, the same number of times _________________________________. This is the ______________________ of mechanics. It is formulated as follows: ________________________________________________________________________________________________________________________________________________. Usually, when a body moves, ______________________________ friction. Therefore, the value of _____________________ of work is always greater than ____________________. The ratio of ________________________________________ to ______________________, expressed as a percentage, is called _________________________________________________________________________________________: ______________.

Mini test.

Your efficiency today in the lesson

2. more than 100%

3. less than 100%

Literature

1 A.V. Peryshkin Physics Grade 7. Moscow: Bustard, 2010

2 G.N. Stepanova Physics 7 workbook part 1. St. Petersburg STP-School, 2003