Determining the equilibrium conditions of the lever, table 15. Application of simple mechanisms. Clarification of the equilibrium conditions of the lever. Example of work done

Purpose 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 downward, 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.

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 leverage and use them to explain results practical work;
• developmental - show students the social and practical significance of the material being studied, 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.

Lesson progress:

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. Summing up.

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 the option practical task, the following result was obtained: the products of force on the 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.

Full text of the material Development of a physics lesson

Lesson developments (lesson notes)

UMK line A. V. Peryshkina. Physics (7-9)

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

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.

Lesson progress

1. Organizational moment (2 min)

2. Repetition. Updating knowledge. (20 min)

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

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:(5min)

• 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 will be selected (by the largest 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)

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

Work 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.

	Force F 1 on the left side of the lever, N	Shoulder l 1, cm	Force F 2 on the right side of the lever, N	Shoulder l 2, cm	Strength-shoulder ratio

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).

1. Triple Goal:

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 development student speeches, visual memory, attention, semantic memory, observation, visual perception, skills to analyze, compare, generalize, forming 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 results force measurements, shoulder strength using tables.
2.3.4. Draw conclusions based on experimental data.
2.3.5. Give examples practical application lever
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.

Hanafina Totygul
Physics lesson summary “Laboratory work. Determining the equilibrium condition of the lever"

Laboratory work No. 5

Determining the equilibrium condition of the lever.

Goals lesson:

1. Formation of educational and cognitive competence through clarification of the equilibrium condition of the lever.

2. Check experimentally at what ratio of forces and their shoulders the lever is in balance.

3. Experimental verification of the moment rule.

1. Safety regulations.

2.Practice tasks and questions:

What is lever?

(Lever represents solid, capable of rotating around a fixed support).

What is called the shoulder of strength?

(The arm of force is the distance from the fulcrum to the line of action of the force).

Formulate a rule lever balance.

(In order to balance with a smaller force, a greater force requires that its shoulder exceed the shoulder of the greater force. Gain in power obtained through lever determined by the ratio of the applied force arms).

Write down the rule formula lever balance.

(F2/F1=l1l2)

Formulate the rule of moments.

(The lever is in balance, if the moment of the force rotating it clockwise is equal to the moment of the force rotating it counterclockwise).

Write down the formula for the rule of moments.

(M1=M2 or F1l1=F2l2)

3. Execution work:

1. By rotating the nuts at the ends balance the lever like this so that it is positioned horizontally.

2. hang two weights on your left shoulder lever at a distance l1=18 cm from the axis of rotation.

3. By trial, set the location on the right shoulder lever, to which three weights should be suspended so that balance the previous two. Measure the distance from this place to the axis of rotation (l2).

4. Assuming that each weight weighs 1N, fill in the blanks in the table.

l1,m F1,H l2,m F2,N M1,Nm M2,Nm

5. Draw a conclusion about the validity of the moment rule.

(The lever is in balance, if the moment of force rotating it clockwise is equal to the moment of force rotating it counterclockwise).

4.Additional task:

Hang three weights to the right of the axis of rotation lever at a distance of 5 cm. Using a dynamometer, determine how much force needs to be applied at a distance of 15 cm from the axis of rotation to the right of the weights, directing it upward to hold lever in balance