Laboratory work on the conditions of equilibrium of a lever. Physics lesson summary “Laboratory work. Clarification of the equilibrium conditions of the lever. Example of work done

Goal of the work: check experimentally at what ratio of forces and their shoulders the lever is in balance. Test the rule of moments experimentally.

From the textbook (§§56, 57) you remember that if the forces acting on the lever are inversely proportional to the arms of these forces, the lever is in equilibrium.

The product of a force and its arm is called the moment of force.

M 1 - moment of force F 1; M 2 - moment of force F 2;

Example of doing the job:

Calculations:

If during work the ratios of the shoulder forces turn out to be not quite equal to the ratios of forces, do not be embarrassed. The lever you are using cannot be called a very accurate device, and some error may be made when measuring the shoulders and forces. So if you get an approximate equality, this is enough to draw the correct conclusion.

Additional task.

The dynamometer will show the force value F 2 ≅1 N.

The forces acting on the lever in this case will be directed as follows: Force F 1 (the force of gravity acting on the weights) will be directed vertically downwards, its shoulder l 1 = 15 cm.

Force F 2 (the elastic force of the dynamometer spring) will be directed vertically upward; her shoulder l 2 = 15 cm.

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 type: combined.

Forms of implementation: collective work with the whole class, work in groups, individual work.

Methods: conversation, story, laboratory work to clarify the conditions of equilibrium of the lever.

The purpose of the lesson: study the simplest and most common simple mechanism - the lever.

Lesson Objectives:

• Educational: consolidate the concepts of simple mechanisms, levers and their role in human life; find out the condition of lever equilibrium, teach how to apply the rule of lever equilibrium.
• Educational: to cultivate cognitive interest in new knowledge, to create conditions for the manifestation of the desire to independently search for new knowledge.
• Developmental: continue to develop skills and abilities to analyze knowledge and draw conclusions, develop attention and observation through a change in educational activities.
• develop practical skills when using devices;
• develop students' creative thinking.

Equipment: computer, projector, ruler lever, set of weights, scissors, lever scales, block, human skeleton, inclined plane.

During the classes

1. Organizational moment (2 min)

2. Repetition. Updating knowledge. (20 minutes)

A) Demonstration: scissors, lever scales, block, lever-ruler, human skeleton. (2 minutes)

Students are asked a problematic question: What unites these devices and devices? (Simple mechanisms - levers, inclined plane)

Name these simple mechanisms, what type of levers do they belong to?

B) Answer the questions:(5 minutes)

• What are simple mechanisms and what are they for?
• What is a lever (1st kind, 2nd kind)?
• What is a shoulder?
• Lever balance rule?
• What is moment of force?
• What is the rule of moments?

B) Working with the presentation.(9 min)

• Make a block diagram of the types of simple mechanisms. (3 min)
• Divide simple mechanisms into two groups. (5 min)
• Examination. (criteria presented in presentation) (1 min)

D) The use of simple mechanisms - levers.(4 min)

Work in mini-groups (2 people) with elements of competitive games.

Each group is given a sheet with a picture of a human skeleton, and there is a demonstration model on the table.

Task: in 1 minute, circle all possible levers using the example of a human skeleton.

At the end of the time, the groups change sheets and the number of circled levers is counted (criteria are presented in the presentation). Three winners are selected (based on the highest number). The works are being assembled. (self-assessment + teacher assessment)

During a joint discussion, the layout shows all possible levers.

3. Performing laboratory work. (18 min)

(Children are given printouts that they fill out as they complete the work)

Goal of the work: check experimentally at what ratio of forces and their shoulders the lever is in balance. Test the rule of moments experimentally.

Progress:

1. Hang one weight on the hook on the right side at a distance of 12 cm from the axis.
2. Balance the lever with one weight. Measure your left shoulder.
3. Balance the lever again, but with two weights. Measure your left shoulder.
4. Balance the lever again, but with three weights. Measure your left shoulder.
5. Assuming that each load weighs 1 N, I record the data and measured values ​​in a table.

1. Calculate the force ratio and the shoulder ratio for each of the experiments and write the results obtained in the last column of the table.
2. Check whether the experimental results confirm the condition of equilibrium of the lever under the action of forces applied to it and the rule of moments of forces.

(F₁)/(F₂)=(l₂)/(l₁).

M 1 = F 1 * l 1 = = H/m

M 2 = F 2 * l 2 = = N/m

7. Draw a conclusion.

Conclusion: … .

4. Lesson summary. (1 min.)

Conclusion: No matter how many times the strength has increased, the more times the leverage has decreased. When the moments of force are equal, the lever rotates clockwise and counterclockwise, it is in equilibrium.

5. Homework.

(given to each person individually at the end of the lesson) (1 min)

1. § 60, ex. 30(1-3.5).
2. Task (p.180)*,
3. * Using a ruler, measure the lever arms (scissors, wrench, nail puller, tin snips) and determine the gain in strength of the selected simple mechanisms.

6. Reflection. (on the received pieces of paper) (3 min)

Method of non-judgmental control “Mini-review”.

Write in one sentence:

• on one side of the sheet “Important” (what was important in class today),
• on the other - “Unclear” (what remains unclear).

The lesson on developing experimental skills has the following goals:

• educational - to form the concepts of the rules and conditions of equilibrium, the rule of moments, to show its significance in science; be able to explain the rules for using levers and apply them to explain the results of practical work;
• developmental - show students social and practical significance the material being studied, to develop the ability to generalize experimental data, compare and draw conclusions,
• educational - to cultivate a culture of mental work, to continue work on the formation of communication skills, positive motivation for learning, aesthetic perception of the world, to instill a love of science and knowledge.

Equipment for the lesson: computer, projector, lever on a tripod, set of weights, ruler.

During the classes:

I. Motivation.

1.What rules did we learn in the last lesson?

(- lever rule and moment rule).

2.What do you need to know to write down these rules?

(- shoulder and strength)

3.Write down these rules.

Rule of moments: M 1 = M 2;

Lever rules: F 1 *L 1 = F 2 *L 2

4. In what very familiar and often used devices do we find levers?

(scissors, wire cutters, lever scales).

II.Updating basic knowledge.

1. Explain the purpose of these objects (projection of drawings on the board).

• Scissors for cutting paper sheets.
• Scissors for cutting metal sheets.
• Lever scales for determining body weight.

2. Why do some scissors cut thick layers of paper, while others do not?

Scissors operate based on the rule of lever equilibrium. By applying a small force to the long part of the scissors on one side, we get more force on the short part of the scissors on the other side. In order for scissors to cut a thick layer of paper or cardboard, their blades are made short and their handles long.

3. Apply and explain the rules for each of these items:

a) the length of the handle and the length of the blade of paper scissors are almost the same because it does not require much effort;

b) the long handles and short blades of scissors for cutting metal sheets create a large force at the point of contact between the scissors blade and the metal; no matter how many times they are shorter, the force generated during application is the same number of times greater;

c) lever scales have the same arms, which means the force acting on the left and right sides of the scales is the same. Knowing the mass of the weights, determine the mass of the load.

III. Laboratory work No. 5 “Finding out the conditions of equilibrium of the lever”

(for three options):

Option 1:L 1 =18cm; F 1 =2 N; F 2 =3H; L 2 =?

Option 2: L 1 =12cm; F 1 =2H; F 2 =3H; L 2 =?

Option 3:L 1 =18cm; F 1 =1H; F 2 =3H; L 2 =?

Directions for work:

1.Secure the lever to the tripod.

2. Balance the lever without weights using special bolts.

3. Balance the lever using a set of weights and a ruler according to the instructions of your option.

4.Draw a balanced lever on the diagram.

5.Measure the length of the shoulder L 2.

6. Determine the moments of forces M1 and M2.

7.Compare the value of M1 and M2.

8.Draw a conclusion.

IV. Summarizing.

1. Conclusion about the validity of the moment rule.

(Report from each option).

By placing sets of weights at the specified distance, we got the following result:

the product of the force on the arm of this force on the left side of the lever and on the right side of the lever is the same.

This means that the equilibrium condition is satisfied, the moment of force is the same.

General conclusion from the experiment:

Using different sets of weights in all groups performing a variant of the practical task, the following result was obtained: the products of force per arm of this force on the left side of the lever and on the right side of the lever are the same.

Consequently, the equilibrium condition of the lever is satisfied, and the moment rule is valid. M1= M2.

2. Reflection questionnaire.

1.1 educational: create conditions for students to clarify the equilibrium conditions of the lever.
1.2 developing: expand the natural science system of views on the processes occurring in nature.
1.3 educational: form on this educational material mental, moral, aesthetic, universal worldview, development of independence in putting forward hypotheses and formulating conclusions, developing a communicative culture, the ability to evaluate oneself and one’s comrades.

2. Tasks:

2.1. Learning objectives aimed at achieving personal learning outcomes.
2.1.1. To promote self-development and self-education of students based on motivation for learning and knowledge.
2.1.2. Continue the development of students’ speech, visual memory, attention, semantic memory, observation, visual perception, skills to analyze, compare, generalize, and form an idea of ​​the computer as a teaching tool.
2.1.3. Form a holistic picture of the world.
2.1.4. Form a conscious, respectful and friendly attitude towards another person and his opinion.
2.1.5. Develop the ability to control the process and results of activities.
2.2. Learning objectives aimed at achieving math-subject learning outcomes.
2.2.1. Cognitive: develop cognitive activity, continue to work on developing the ability to collect, systematize and apply information on the topic, apply and transform sign-symbolic means to solve problems.
2.2.2. Communicative: continue to work on developing the ability to work in pairs, organize educational cooperation and joint activities with the teacher and peers.
2.2.3. Regulatory: continue to work on developing the ability to independently plan ways to achieve goals and consciously choose effective ways problem solving.
2.3. Learning objectives aimed at achieving subject-specific learning outcomes.
2.3.1. Continue to develop general educational and general cultural skills in working with information, and the ability to apply formulas in practice. Understand the meaning of the concepts of leverage, moment of force, physical quantity of force, and their units of measurement.
2.3.2. Be able to describe and explain physical phenomena based on the equilibrium condition of a lever.
2.3.3. Present the results of measurements of force and leverage using tables.
2.3.4. Draw conclusions based on experimental data.
2.3.5. Give examples of the practical use of leverage.
2.3.6. Solve problems using the conditions of equilibrium of a lever and moment of force.
2.3.7. Check experimentally at what ratio of forces and their shoulders the lever is in balance.
2.3.8. Test the rule of moments experimentally.

1.1 educational: create conditions for students to clarify the equilibrium conditions of the lever.
1.2 developing: expand the natural science system of views on the processes occurring in nature.
1.3 educational: use this educational material to form a mental, moral, aesthetic, universal worldview, develop independence in putting forward hypotheses and formulating conclusions, cultivate a communicative culture, and the ability to evaluate oneself and one’s comrades.

2. Tasks:

2.1. Learning objectives aimed at achieving personal learning outcomes.
2.1.1. To promote self-development and self-education of students based on motivation for learning and knowledge.
2.1.2. Continue the development of students’ speech, visual memory, attention, semantic memory, observation, visual perception, skills to analyze, compare, generalize, and form an idea of ​​the computer as a teaching tool.
2.1.3. Form a holistic picture of the world.
2.1.4. Form a conscious, respectful and friendly attitude towards another person and his opinion.
2.1.5. Develop the ability to control the process and results of activities.
2.2. Learning objectives aimed at achieving math-subject learning outcomes.
2.2.1. Cognitive: develop cognitive activity, continue to work on developing the ability to collect, systematize and apply information on the topic, apply and transform sign-symbolic means to solve problems.
2.2.2. Communicative: continue to work on developing the ability to work in pairs, organize educational cooperation and joint activities with the teacher and peers.
2.2.3. Regulatory: continue to work on developing the ability to independently plan ways to achieve goals, consciously choose effective ways to solve problems.
2.3. Learning objectives aimed at achieving subject-specific learning outcomes.
2.3.1. Continue to develop general educational and general cultural skills in working with information, and the ability to apply formulas in practice. Understand the meaning of the concepts of leverage, moment of force, physical quantity of force, and their units of measurement.
2.3.2. Be able to describe and explain physical phenomena based on the equilibrium condition of a lever.
2.3.3. Present the results of measurements of force and leverage using tables.
2.3.4. Draw conclusions based on experimental data.
2.3.5. Give examples of the practical use of leverage.
2.3.6. Solve problems using the conditions of equilibrium of a lever and moment of force.
2.3.7. Check experimentally at what ratio of forces and their shoulders the lever is in balance.
2.3.8. Test the rule of moments experimentally.