Natalia Vazhenina
So, let’s say you have a desire and need to take part in one or another webinar. Where to begin?
STEP 1.
We carefully study the provisions of this webinar. If you have any questions, write to the organizer and clarify.
STEP 2.
Submit an application and register for the webinar. The organizers usually describe in detail how to do this in the regulations.
STEP 3.
You will receive an email confirming that you have successfully registered to participate in the webinar. Such a letter usually contains a link to the so-called webinar room (training room).
What is a webinar room and what does it consist of?
The webinar room looks like this:
On the right is a large window where a presentation on the topic under discussion is shown during the webinar.
At the top left is a screen where a video is broadcast on which the presenter talks and shows the webinar material.
At the bottom left is a chat where you can write questions to the presenter from your computer during the webinar. And he will answer you live.
Here you can see it better.
That's all the wisdom! I hope the information is useful!
Publications on the topic:
Consultation for teachers “What is pedagogical technology”, “What is health-saving technology” Pedagogical technology is a direction of pedagogy whose goal is to increase the efficiency of the educational process, guaranteed.
Consultation for teachers “What is a portfolio and why does a future first-grader need it?” The emergence of the concept of “portfolio” in the pedagogical lexicon is associated with the introduction of new approaches in education and the assessment of its new forms. IN.
Consultation for teachers “What is a representative system” The Federal State Educational Standard for Preschool Education prescribes the basic principles of preschool education, one of which is the construction of educational activities.
Consultation for teachers “Humanization of pedagogy. What it is?" It is well known that a person is formed by the totality of relationships into which he enters. This may be relations with the state, its laws.
One of the main conditions for the introduction of information technology in preschool educational institutions is that specialists who know the technical capabilities should work with children.
“Reading is a window through which children see and know themselves.” V. A. Sukhomlinsky “A book is a vessel that fills us, but by itself.
Consultation for parents “What is isothread” The purpose of applied art is to “animate with the power of art” an object of material purpose, to give it meaning, to make it.
Solving problems on the topic: “Simple mechanisms.”
Repetition task.
1. What are simple mechanisms? Give examples of simple mechanisms.
2. For what purpose are simple mechanisms used?
3. What is leverage? Formulate the equilibrium condition for the lever.
4. What is called the moment of force? Formulate the rule of moments.
5. What is a block? What types of blocks are there? For what purpose is a fixed block used? moving block?
6. Formulate the “golden” rule of mechanics.
7. Do simple mechanisms provide benefits in work?
8. Solving problems No. 1, No. 2, No. 3, No. 4.
9. Task cards:
Homework: everyone - repeat § 59-60
On “4” - exercise 31(1,2)
No. 1. Which rod is easier to break into two equal parts - long or short? Why?
No. 2. Is it easier to cut cardboard with scissors: placing it towards the ends of the scissors or placing it closer to their middle?
No. 3. If two guys of different masses are swinging on a board thrown over a log, should they sit at the same distance from the support?
No. 4. When the lever is in equilibrium, a force of 60 N acts on its larger arm, equal to 80 cm, and a force of 240 N on the smaller one. Determine the length of the smaller arm.
No. 5. The arms of the lever in equilibrium are 40 cm and 20 cm. A force of 60 N is applied to the larger arm. What force is applied to the smaller arm?
No. 6. Forces of 25 N and 150 N act at the ends of the lever. The distance from the fulcrum to the smaller force is 21 cm. Determine the length of the lever if it is in equilibrium.
No. 7. How much weight can a boy weighing 400 N lift using a moving block? (do not take into account the weight of the block)
No. 8. What load can be lifted using a moving block weighing 20 N if the rope is pulled with a force of 150 N? How long will the free end of the rope have to be pulled to lift this load to a height of 2 m?
No. 9. Using a movable block, a load was raised to a height of 10 m, applying a force of 120 N. What work was done in this case?
On “4” - exercise 31(1,2)
On “5” - Using a ruler and a 5 ruble coin (its weight
equals 7 g), determine the weight of the pencil. Describe how you do it
No. 1. Which rod is easier to break into two equal parts - long or short? Why?
No. 2. Is it easier to cut cardboard with scissors: placing it towards the ends of the scissors or placing it closer to their middle?
No. 3. If two guys of different masses are swinging on a board thrown over a log, should they sit at the same distance from the support?
No. 4. When the lever is in equilibrium, a force of 60 N acts on its larger arm, equal to 80 cm, and a force of 240 N on the smaller one. Determine the length of the smaller arm.
No. 5. The arms of the lever in equilibrium are 40 cm and 20 cm. A force of 60 N is applied to the larger arm. What force is applied to the smaller arm?
No. 6. Forces of 25 N and 150 N act at the ends of the lever. The distance from the fulcrum to the smaller force is 21 cm. Determine the length of the lever if it is in equilibrium.
No. 7. How much weight can a boy weighing 400 N lift using a moving block? (do not take into account the weight of the block)
No. 8. What load can be lifted using a moving block weighing 20 N if the rope is pulled with a force of 150 N? How long will the free end of the rope have to be pulled to lift this load to a height of 2 m?
No. 9. Using a movable block, a load was raised to a height of 10 m, applying a force of 120 N. What work was done in this case?
Homework: everyone – repeat §
On “4” - exercise 31(1,2)
On “5” - Using a ruler and a 5 ruble coin (its weight
equals 7 g), determine the weight of the pencil. Describe how you do it
Experimental task No. 1.
Checking the equality of work on the lever.
Devices and materials: lever on a tripod, set of weights, ruler.
2. Hang three weights on the left side of the lever and one weight on the right. By moving the weights, achieve balance of the lever.
3. Deflect the lever to a certain angle in the vertical plane and measure the paths traversed by the points of application of gravity forces (see figure).
4. Calculate the work done by both gravity forces and compare their numerical values.
5. Write down the results of measurements and calculations in a notebook.
6. Answer the questions:
· How many times does one gain in strength by using leverage?
· How many times do they lose along the way when using leverage?
· Is it possible to get a win in work using a lever?
Experimental task No. 2.
Measuring body weight using a lever.
Devices and materials: lever on a tripod, ruler, dynamometer, weight weighing 1N, metal cylinder.
The order of work.
1. Rotating the nuts on the ends of the lever, set it to a horizontal position.
2. Hang a metal cylinder to the left side of the lever, and a weight weighing 1N to the right. Experimentally achieve balance between the lever and the load.
3. Measure the arms of the forces acting on the lever.
4. Using the lever equilibrium rule, calculate the weight of the metal cylinder.
5. Measure the weight of the metal cylinder using a dynamometer and compare the result with the calculated one.
6. Write down the results of measurements and calculations in your notebook.
7. Answer the questions: will the result of the experiment change if:
· balance the lever with a different arm length of the forces acting on it?
· hang the cylinder on the right side of the lever, and the balancing weight on the left?
Experimental task No. 3.
Devices and materials: scissors, ruler.
The order of work.
2. Measure the force arms.
3. Calculate approximately the gain in force when using scissors, using the lever equilibrium condition: F1: F2 = l2: l1
5. Answer the question: how should the material being cut be positioned in the scissors to get the greatest gain in strength?
Experimental task No. 4.
Calculation of the gain in the strength of instruments in which leverage is applied.
Devices and materials: wire cutters, ruler.
The order of work.
1. Familiarize yourself with the design of the tool offered to you, which uses a lever: find the axis of rotation, the points of application of forces.
2. Measure the force arms.
3. Calculate approximately the gain in force when using pliers, using the lever equilibrium condition: F1: F2 = l2: l1
4. Write down the results of measurements and calculations in a notebook.
5. Answer the question: how should you hold the pliers in your hand to get the greatest gain in strength?
Experimental task No. 5.
Calculation of the gain in the strength of instruments in which leverage is applied.
Devices and materials: pliers, ruler.
The order of work.
1. Familiarize yourself with the design of the tool offered to you, which uses a lever: find the axis of rotation, the points of application of forces.
2. Measure the force arms.
3. Calculate approximately the gain in force when using pliers, using the lever equilibrium condition: F1: F2 = l2: l1
4. Write down the results of measurements and calculations in a notebook.
5. Answer the question: how to hold pliers
in hand to get the biggest gain in strength?
Stage 1 (grades 5-6).
Form of work: Collective and group.
Key tasks:
- A system of creative homework (come up with a story, choose proverbs, poems, paintings by artists on a given topic).
- A system of creative tasks in lessons (describe, come up with a story on a given topic, conduct research).
- Carrying out practical tasks in groups.
- Manufacturing of instruments and devices.
- Students work together with high school students on projects.
Stage 2 (grades 7-9).
Form of work: individual, group, collective.
Lesson forms: auction lesson, trial lesson, creative laboratory lesson.
Key tasks:
- A system of tasks for working in groups (research, problem solving, compiling tables, solving qualitative problems).
- A system of individual creative tasks (studying the phenomenon of wetting, determining the gain in the power of simple mechanisms).
- Involving all students in a creative project on a chosen topic.
Stage 3 (grades 10-11)
Form of work: group, individual.
Lesson forms: lesson-seminar (role-playing game), lesson-presentation.
Key tasks:
- Completion of a compulsory creative assignment in 10th grade.
- Preparation of abstracts.
- Doing a home test.
- Preparation of materials for lessons and seminars.
- Preparing presentations for lessons.
- Students’ work with collections of problems “Experiment”, “Olympiad”.
I have developed a series of different lessons to actively involve students in activities.
Form of work: individual and group.
Duration: 45 minutes.
The date of the: March, 2007
Peculiarities: Using a presentation (presentation slides are attached below), drawing up summary tables, performing creative tasks in groups, conducting reflection.
Educational:
- 1) Test students’ ability to determine gains in strength.
- 2) Systematize the acquired knowledge by compiling a general table “Simple mechanisms”.
- Test your ability to apply acquired knowledge to solve practical problems.
Developmental:
- Continue to develop students’ thinking by applying acquired knowledge to solving practical problems.
- Continue the development of mental operations: analysis, synthesis, generalization.
Educational:
- Development of communication skills.
- Development of teamwork skills (mutual respect, mutual assistance and support).
Lesson plan:
| Lesson steps | Job No. | Kind of activity | Form of work | time |
| 1 | 1 | Practical task. “Calculate the power gain of simple mechanisms on the table.” |
Group. | 8 min. |
| 2 | Theorists at the board must justify the gains in the power of simple mechanisms theoretically. | Individual. | 8 min.. | |
| 3 | Filling out the general table “Simple mechanisms”. | Group. | 5 minutes. | |
| 4 | Practical work: Determine the gain in strength forearms. |
Group. | 5 minutes. | |
| 2 | 1 | Discussion of qualitative issues. | Group | 8 min. |
| 3 | 1 | Taking a test on the topic. | Individual | 8 min. |
| 4 | 1 | Reflection. | Individual | 3 min |
Teacher: Good afternoon. The topic of our lesson: “Simple mechanisms for us and around us.”
Take the green sheets of paper on your desks, you see a scale, mark it with a tick where you are now. Set the sheets aside.
Teacher: Since time immemorial, people have been using various objects and devices - simple mechanisms - to perform work.
What engineering solution do you think was made by the ancient architects, who were able to lift and install millions of heavy blocks in their place in a relatively short period of time? There are many hypotheses on this matter. Most likely, they used simple mechanisms to lift the blocks.
The outstanding scientist of the ancient world, Archimedes, in his works sets out the laws of the lever and concludes that theoretically, with the help of a lever, you can lift any body, including the earth.
Remember what simple mechanisms are there?
Students: lever, gate, block, inclined plane.
Teacher: What are they needed for?
Students: To get the winnings in strength.
Teacher: Today in the lesson we will remember what simple mechanisms there are and where we meet them.
You will complete the tasks in groups, and at the end of the lesson the result of your work will be assessed.
Task No. 1. On the board, 1 person from the group (theorists) must justify the gain in the strength of various mechanisms.
Task No. 2. The remaining members of the groups perform an experimental task to calculate the gain in the strength of simple mechanisms (scissors, wire cutters, block, inclined plane).
Slide number 4
A discussion of completed tasks 1 and 2 is held.
Task No. 3. Now let’s summarize the knowledge gained by filling out the “Simple Mechanisms” table.
Teacher: Let's check the completed tables.
Slide number 6
Teacher: Let's draw a conclusion. Why do we need simple mechanisms?
Students: We need mechanisms to obtain a gain in strength or distance, but we will not get a gain in work.
2. Teacher: A simple lever mechanism has an important property that determines its widespread use in natural mechanisms, animal and human skeletons. Lever mechanisms in the skeletons of animals and humans are almost all bones that have some freedom of movement: the bones of the limbs, the lower jaw, the phalanges of the human fingers.
Name where in our body we meet this lever?
Skull in the sagittal plane. The axis of rotation is the point of articulation of the skull with the first vertebra, R is the force of gravity of the head, F is the force of muscle traction.
Forearm bone. O is the fulcrum in the bone of the forearm, F is the strength of the muscles that flex the forearm, R is the weight of the load.
Foot of the leg. F is the force acting from the shin on the top of the ankle,
R is the force exerted by the Achilles tendon on the heel.
Task 4. Calculate the payoff in your hand strength.
Teacher: What power gain did you receive? Why is such a mechanism needed?
3. Teacher: Various simple mechanisms that surround us allow us to gain gains in strength or distance and make our lives more convenient.
Therefore, we need to know and take into account the peculiarities of their action.
Let's try to apply our existing knowledge to solve problems.
Answer the questions:
- Why is the door handle not attached in the middle of the door, but at its edge?
- If 2 boys of different masses are swinging on a board thrown over a log, should they sit at the same distance from the support?
- What load can be lifted using a moving block weighing 20 N if the rope is pulled with a force of 150 N?
- Why does a wing nut have blades?
- Why is it harder to break 1/4 of a match than a whole one?
What will the dynamometer show?
The correct solution to the problem:
4. Let’s summarize the work in groups. Well done... the rest need to catch up. Now the work will be done by everyone individually, take the white sheets and complete the test. At the end of the work, you hand over the sheets and each of you will receive another mark for the work completed.
Slide number 10
Now pay attention to the correct test solution:
Slide number 11
The results obtained are discussed.
Teacher: I suggest doing creative homework. Write down:
5.Teacher: Let's summarize the activities for the lesson. Take the green sheets and mark with two pluses the place where you are now. Fill out the lesson reflection table below.
Teacher: This concludes the lesson. Thanks to all!
________________________________________________
_______________________
Reflection sheet:
Last name, first name_____________________________________________
_______________________
1. My mood:
2. Values for you of this work:
- The most important thing is 1
- Important – 2
- Not very important – 3
- Not important at all – 4
Strive to comprehend science more and more deeply,
Thirst for the knowledge of the eternal.
Only the first knowledge will shine upon you,
You will find out: there is no limit to knowledge.
Ferdowsi
Hakim Abulqasim Mansur Hasan Ferdowsi Tusi (935–1020) - Persian poet.
BOX OF QUALITY PROBLEMS IN PHYSICS: ELEMENTS OF STATICS
balance of bodies, moment of force, simple mechanisms...
Didactic materials on physics for students, as well as their parents;-) and, of course, for creative teachers. For those who love to learn!
Your attention 75
qualitative problems in physics on the topic of: “Elements of statics: balance of bodies, moment of force, simple mechanisms”.
We will accompany the tasks with educational notes and comments - for the curious We will give detailed answers to some problems;-) In the tradition of green pages, we will treat ourselves masterpieces of world painting…
And also ;-) let's get acquainted with some secrets leaning Nevyansk tower - an architectural pearl of the Urals, shrouded in legends, right up to the flag-weathervane with the Demidovs’ coat of arms...
Task No. 1
Before you are three pictures - three wells. What simple mechanisms underlie the operation of these simple but very effective devices that make it easier to raise water from a well? Support your answer with schematic drawings.
Three wells...
crane |
gate |
block |
||
Mikeshin Mikhail Osipovich(02/21/1835–01/31/1896) - Russian painter.
George Hardy(George Hardy; 1822–1909) – English genre painter.
Daniel Ridgeway Knight(Daniel Ridgway Knight; 03/15/1839–03/09/1924) - American genre painter.
Task No. 2
“Yamskaya Sloboda”, 1927. Andrey Platonovich Platonov
“...In the middle of the settlement stood a two-story old house. Near it there is a well, and near the well there is a round barn - a dungeon for a horse. In that dungeon, all day long the horse circled in a narrow place, dragging a wooden carrier. On the carrier, ropes were twisted and untwisted, which carried water from the well in buckets. The water was poured into a large vat, and from the vat it was poured into troughs. From the trough, the peasants who came to the settlement to the bazaar, watered the horses for a penny per head, and people drank for free ... "
What simple mechanisms used to raise water from a well are discussed in this passage?
Task No. 3
What type of mechanical movements occur with different parts of the gate during use?
Answer: Rotational (wheel, shaft) and translational (rope, lifted load - bucket of water).
Task No. 4
Firefighters and climbers sometimes use a stationary, simple pulley to lift themselves up a rope or cable. Does this result in a gain in strength relative to the weight of the load being lifted?
Answer: The result is a double gain in strength.
I didn’t expect that problem No. 4 “about firefighters and climbers” would cause such heated debate. Some comments are hidden (not deleted!) due to excessive aggression and confusion. At the same time, it is apparently worth examining the solution to this simple problem in more detail.
Taking this opportunity, I decided to add to the page a reproduction of a painting by Rostislav Vovkushevsky "Climbers". For some it’s just a picture, but for others it’s wonderful memories of youth...
Vovkushevsky Rostislav Ivanovich(03/22/1917–08/14/2000) - Soviet Russian painter, teacher, member of the St. Petersburg Union of Artists.
Explanations for solving the problem “about firefighters and climbers”
So, a stationary block does not provide a gain in strength if, for example, one person pulls another person out of a well or cave. But, in the case when a person lifts himself, he applies force that is half his weight. Since in this case the person’s weight is distributed equally into two parts of the cable or rope (on opposite sides of the block).
F = P/2 = mg/2
It turns out that the gain in strength is doubled.
It should be taken into account that no one has canceled the “golden rule” of mechanics ;-) It was formulated in ancient times as follows: “what we gain in strength, we lose in travel”. This position is so general and at the same time so important that it has received the name "golden rule" of mechanics.
It turns out that we will achieve a double gain in strength at the cost of a double loss along the way. In other words, to lift oneself with the help of a fixed block, say, to a height of 15 meters, a person must, moving the cable with his hands, pull it out 30 meters.
Thus, the work a climber lifting himself will do is the same as a person standing on the ground and lifting a climber to the same height.
A = F × 2h = mg/2 × 2h = mgh
Let's summarize:
Received the winnings in power twice ;-)
We got a double loss on the way.
We didn’t get any benefits from our work :-(
There is no talk about work in the condition of task No. 4 “about firefighters and climbers,” but for the sake of completeness, let it be... Apparently those who stirred you up do not understand the difference between strength and work...
Problem #5
If two guys of different weights are swinging on a board thrown over a log, should they sit at the same distance from the support?
Frederick Morgan(Frederick Morgan; 1856–1927) – English genre painter.
Problem #6
Why is a screwdriver made with a thick handle?
Answer: The large diameter of the handle increases the leverage of the force we apply to be able to reduce this force. For the same reason, the door key is always made with the wide part where it is held by the hand, just like a corkscrew. The corkscrew, thanks to its spiral mechanism, performs another transformation: the rotation of the handle, in which we apply a small force and perform a large movement, is converted into a small movement of the tip of the corkscrew into the depth of the cork, which without this rotation would require a large force. The same principle used in a lever is used in pliers...
Problem No. 7
Why is it easier to cut thick cardboard with the middle of scissors than with the ends?
Answer: This makes it possible to reduce the force applied to the scissor handles.
Problem No. 8
Office scissors have very long blades. Is it profitable?
Answer: The loss in strength is not significant here, but the gain in speed is of great importance.
Johan August Malmström(Johan August Malmström; 10/14/1829–10/18/1901) - Swedish genre painter.
Problem No. 9
Why does the product sometimes get pushed out of the scissors when cutting?
Answer: The resultant of the forces acting on the object being cut from the side of the scissors blade is not zero and is directed from the axis of the scissors. If it is greater than the friction force, then the product is pushed out.
For the curious: Scissors known from the 3rd century BC - found during excavations of cultural monuments of Celtic tribes. They consisted of two knives connected by an arched springy metal plate. Similar scissors are still used today for shearing sheep. Modern type scissors (made of two articulated knives) appeared around the 8th century AD in the Middle East. In Rus', the oldest articulated scissors were found in the Gnezdovo Kurgans, an archaeological reserve in the Smolensk region of Russia (the settlement of Gnezdovo was most likely founded at the beginning of the 10th century).
Problem No. 10
Where in the door is the handle placed to make it easier to open the door?
Answer: The handle is placed at the edge of the door to increase the leverage and thereby make opening the door easier.
Problem No. 11
Why is it easier to climb a flat staircase than a steep one?
Problem No. 12
Why do roads in mountainous areas zigzag?
(06.06.1844–13.02.1905) - Russian genre painter, academician, full member of the Imperial Academy of Arts, member of the Association of Traveling Art Exhibitions, teacher.
Auvergne is an administrative region of France located on the territory of the Central Massif. The highest peak is Mount Sancy (1886 m). Auvergne is rich in mineral waters and thermal springs.
Problem No. 13
What simple mechanisms underlie the tools and devices that workers use to build a road in the painting by Joseph Vernet?
Claude Joseph Vernet(Claude Joseph Vernet; 08/14/1714–12/03/1789) - French painter.
Problem No. 14
Why does the presence of significant elevations on a railway section necessitate the use of locomotives with increased power?
Problem No. 15
Why do drivers avoid stopping trains on the rise?
Problem No. 16
What is the easiest way to move a railroad car: by applying force to the body of the car or to the top of the wheel rim?
Answer: In the second case, half the force will be required, since the instantaneous axis of rotation of the wheel passes through the point of contact with the rail.
Problem No. 17
Why doesn't the carriage of a single-rail suspended railway overturn?
Answer: The center of gravity of the car is below the suspension line.
Problem No. 18
If a fast-moving car brakes sharply, its front end goes down. Why?
We'll probably forget how to walk soon
The habit of driving already lives in us
Walking just two steps is painful
A hundred kilometers by car doesn't count
Cars, cars literally filled everything
Where centuries-old dust lay
The car left its mark...
"Cars"- song of the Soviet ensemble "Funny boys", 1987
words: Mikhail Shabrov, music: Vladimir Matetsky.
Alan Fearnley(Alan Fearnley) – British artist, master of “automotive” painting.
Problem No. 19
Why do cars, bicycles, etc. Is it better to put brakes on the rear wheels rather than the front wheels?
Answer: In order not to create moments of force that overturn the car in a vertical plane and turn it in a horizontal plane, which may arise when braking the front wheels.
Problem No. 20
To pull out a stuck car, use the following technique. A long, strong rope is tied tightly to a tree or stump near the road and to the car so that the rope is taut. Then they pull the middle of the rope at a right angle in its direction. What is this technique based on?
Answer: The technique is based on a huge gain in strength on the cable at a large angle between the component forces.
Problem No. 21
Consider simple mechanisms, the principles of which are used in a bicycle (steering wheel, pedal, gear). In which of them do they gain in strength, and in which do they gain in speed?
Problem No. 22
At what position of the bicycle pedal will the moment of the force acting on it, directed vertically, be greatest? equal to zero?
Answer: The moment is zero at the top and bottom points, maximum in the horizontal position.
Oscar Claude Monet(Oscar-Claude Monet; 11/14/1840–12/05/1926) - French landscape painter, one of the founders of impressionism.
Problem No. 23
A man, in order to avoid slipping on an icy slide, runs away from it. Why is this appropriate?
Problem No. 24
Why do people walk on slippery ice in small steps?
Answer: On ice, the friction force is small, and with large steps a person bends strongly. As a result, the moment of gravity may not be compensated by the moment of friction and the person will fall.
Problem No. 25
Why do speed skaters wave their arms when accelerating?
Answer: The sharp movements of the skater's legs cause the appearance of moments of forces that tend to rotate his body around a vertical axis. Therefore, the skater swings his arms in time with the movement of his legs so that with the movement of his arms he creates moments of forces that counteract and compensate for the moments of forces caused by the movement of his legs.
Problem No. 26
A shovel is a well-known garden tool for digging up soil. What simple mechanism is used in this wonderful instrument? Why does it take less effort to work with a well-sharpened garden shovel?
Peder Severin Kroyer(Peder Severin Krøyer; 07/23/1851–11/21/1909) - Danish painter.
Abruzzo- an agricultural region in Italy, located in the middle part of the Apennine Peninsula on the Adriatic coast.
Problem No. 27
Why can you lift more weight with your arm bent at the elbow than with your arm extended?
Answer: Reducing the lever arm makes it possible to increase the weight of the load being lifted.
Problem No. 28
Explain the workings of the human hand and foot using the rule of leverage.
Problem No. 29
Explain the action of the jaw as a lever, show where the points of application of forces are and why there is a gain in strength.
Problem #30
Should you spread your legs wide apart when lifting heavy weights, or should you keep them together?
Answer: It is necessary, since the center of mass of a person with his legs spread wide apart is lower and he is more stable.
Problem No. 31
A rocker is a wooden device used to make it easier to carry two buckets of water, buckets, baskets... and other loads. What is the feasibility of using this device?
Edwin Thomas Roberts(Edwin Thomas Roberts; 1840–1917) – British painter.
Eugene de Blaas(Eugenio de Blaas; 07/24/1843–02/10/1932) - Italian artist who painted in the style of academic classicism.
Problem No. 32
The load is carried on a stick slung over the shoulder. How does the position of the load (closer or further from the shoulder) affect the amount of force with which the stick acts on the shoulder, and the force with which the hand must hold the stick in balance?
Answer: The closer the load is to the shoulder, the less force with which the hand must hold the stick. Therefore, the force of pressure of the stick on the shoulder, equal to the sum of the weight of the load and the force of the hand, will be less.
Problem No. 33
Why does a person carrying a heavy suitcase or bag in one hand lean in the opposite direction?
Problem No. 34
Why does a person carrying a heavy load on his back lean forward?
Answer: To place the center of gravity of your body with a load on the support area.
Julien Dupre(Julien Dupre; 03/19/1851–04/15/1910) - French artist, representative of realism.
Problem No. 35
Why can't you get up from a chair without tilting your body forward?
Answer: If you do not tilt your body forward, then the vertical line drawn through the person’s center of gravity will not intersect the area of support (feet).
Problem No. 36
Why is it easier to cut meat not by simply pressing on the knife, but by pressing and moving the knife back and forth?
Answer: When a knife moves, its “cutting section” is not a section perpendicular to the cutting edge, as is the case when we simply press on the knife, but a section that makes a certain angle with the line of the tip, the smaller the higher the speed of the knife.
Problem No. 37
Why is the saber given a curved shape, convex on the side of the blade?
Answer: The properties of steel (strength) do not allow it to be sharpened at an angle less than the limit for a given cutting tool. Otherwise the steel will crumble. Due to the curved shape of the saber, at a given wedge angle, it is possible to reduce the cutting angle by increasing the cheek of the wedge.
Jozef Brandt(Jozef Brandt; 02/11/1841–06/12/1915, Radom) - Polish realist artist.
Problem No. 38
Why are hacksaws with small teeth used for sawing hard metal, and with large teeth when sawing soft metal?
Problem No. 39
It is easier to hold a long rod horizontally by the middle than by the end. Why?
Answer: If you hold the rod in the middle, then you do not need to apply any moment of force to keep the rod in balance. If you hold one of the ends, you need to apply a moment of force.
Problem No. 40
When a stick is held in hands by the ends, it is difficult to break it. If you put the middle of the stick on a stand, then it is easier to break the stick. Explain why.
Problem No. 41
Break a thin sliver in half, break the resulting pieces into two again, etc. Why does it get harder to break every time?
Answer: The shoulders of the forces applied to the chip are reduced.
Problem No. 42
Explain the principle of operation of a catapult. What simple mechanism plays a key role in it? Where are catapults currently used?
Edward John Poynter(Edward John Poynter; 1836–1919) – English painter.
Catapult- a Greek term that refers to any throwing machine.
For the curious: Operating principle of a catapult. Unlike a bow, where kinetic energy is provided by the elasticity of the bent arms of the bow, in catapults and ballistas the energy is stored in twisted bundles (bundles) of low-elastic fibers. A lever inserted at one end into a twisted cord tends to unwind, accelerating the other end of the lever to high speed. Thus each arm of the catapult consists of a horizontal lever, inserted into a harness twisted with a certain force, as well as a base or frame into which the harness is vertically attached. Both arms of the catapult are connected by a string, which can only be pulled back using a winch. A guide beam is installed between the levers for the directed flight of a projectile: a stone in a ballista and an arrow in a catapult. Currently, catapults are used to launch projectiles and aircraft from aircraft carriers. Development is underway to create catapults for launching cargo spaceships from the surface of planets.
Problem No. 43
In what case will a barrel rolled along inclined beams produce more pressure on them at the same height: when they are longer or shorter?
Answer: For longer bars.
Problem No. 44
A wheelbarrow is a simple device consisting of a cargo body, wheels and handles, and is intended for transporting goods. What simple mechanism is used in this device?
Answer: A wheelbarrow is a type of lever. The force of gravity of the load is applied much closer to the axis of the wheelbarrow (which in this case plays the role of the axis of the lever) than the force acting from the human hands. Therefore, a person can lift a load on a wheelbarrow that he is not able to lift directly with his hands. The force acting from the human hands must be directed upward so that the moment it creates relative to the axis of the lever is opposite to the moment of gravity of the load.
Savitsky Konstantin Apollonovich(06.06.1844–13.02.1905) - Russian genre painter, academician, full member of the Imperial Academy of Arts, member of the Association of Traveling Art Exhibitions, teacher.
Problem No. 45
Why can’t we use lever scales to verify that the force of gravity changes as we move from the equator to the poles?
Answer: Since two forces equal to the force of gravity are balanced on the lever. A change in one of them occurs simultaneously with a change in the other.
Problem No. 46
An adult and a child need to cross the stream: one from the left bank, the other from the right. There is a board on each bank, but the boards are slightly shorter than the distance between the banks. How can they cross from one bank to the other? Accompany your answer with a drawing.
Problem No. 47
There are two cast iron plates of the same mass. The length of one slab is twice as long as the other. Both slabs are lifted by the edge with a turn near the edge that forms the width of the slab and placed vertically. Which slab requires more force to lift?
Answer: The same force is required, equal to half the gravity of the plate.
Problem No. 48
Levers that are used in reverse;-) Levers are not always used to do work using less force. Sometimes it's important to win the move, even if it means using a lot of force. This is what a fisherman does when he needs to pull out a fish and move it over a long distance. At the same time, he uses the fishing rod as leverage. Comment on the above using a schematic diagram.
Pryanishnikov Illarion Mikhailovich(04/01/1840–03/24/1894) - Russian artist and teacher, master of genre painting, full member of the St. Petersburg Academy of Arts, one of the founders of the Wanderers Association.
Problem No. 49
Two weights of the same material are balanced on a lever, but one weight is twice as heavy as the other. Will the balance of the lever change if the weights are immersed in water?
Answer: Will not change.
Problem #50
Two weights of the same volume, but made of different materials, are balanced on a lever, with one weight being twice as light as the other. Will the balance of the lever change if the weights are immersed in water?
Answer: The balance will be disturbed, and the heavier weight will overwhelm.
Problem No. 51
Two cast iron weights of equal mass are suspended from an equal-arm lever by threads. Will the balance of the lever change if one of them is placed in water and the other in oil?
Answer: It will change: the weight in the oil will go down, and in the water it will rise.
Problem No. 52
Porcelain balls are suspended from an equal-arm lever. If one of the balls is placed in a glass of water and the other in a glass of kerosene, then the lever is in equilibrium. Will the balance be disrupted if the vessels with liquids are removed?
Answer: Yes, it will pull the ball that was in the water.
Problem No. 53
Explain what rocker scales are. What is the basis for the operation of these scales?
Answer: Rocker scales are an equal-arm lever (yoke), at both ends of which bowls for weights and the load being weighed are suspended. For an equal-arm lever, the support is located at an equal distance from the points of application of forces. The operation of such scales is based on the principle of balance.
Leon Augustin Lhermitte(Leon Augustin Lhermitte; 07/31/1844–07/28/1925) - French genre painter, engraver.
I invite readers of green pages to go to the magical kingdom of apples ;-)
§ green page Kursk Antonovka - a symbol of the Kursk region
§ green page Alma-Ata aport - a symbol of the city of Almaty
Problem No. 54
A brass weight was suspended from the balance beam on one side and a cast iron weight of equal mass on the other. Will the scale remain in balance if it is lowered so that both weights are in the water?
Answer: The brass weight will pull.
Problem No. 55
How can you determine the mass of a ruler using a weight of known mass without using a scale? Do it.
Answer: You need to hang a weight from one end of the ruler and place the ruler on a point support so that it is in balance. From the moment equation we find the mass of the ruler.
Problem No. 56
As you know, a stationary block does not give any gain in strength. However, when checked with a dynamometer, it turns out that the force holding the load on a stationary block is slightly less than the force of gravity of the load, and with a uniform rise it is greater than it. What explains this?
Answer: The action of friction force.
Problem No. 57
Why is a heavy load attached to the middle part of the cable connecting the tug and barge during stormy weather?
Answer: To avoid over-tensioning the cable.
Problem No. 58
What will happen if the rowers sitting in the boat, depicted in Vasily Surikov’s painting “Stepan Razin,” begin to move their oars in opposite directions?
Answer: The boat will begin to turn.
Surikov Vasily Ivanovich(01/24/1848–03/19/1916) - Russian painter, master of large-scale historical canvases.
Problem No. 59
The ship has two engines. How will the ship move if the command is given: “Right engine - full forward, left engine - full back!”? The thrust forces of both engines are identical in magnitude.
Answer: Turn under the influence of a couple of forces counterclockwise.
Problem No. 60
What device is depicted in Henry Bacon's painting Towing a Ship? Explain the principle of its operation.
Henry Bacon(Henry Bacon; 839–1912) – American artist.
Answer: Henry Bacon's painting "The Towing of a Ship" depicts capstan(vertical gate - a modified double block), used for pulling ships at berths, as well as removing ship anchors. The capstan spokes play the same role as the larger diameter block in a double block. The equilibrium conditions for the gate are the same as for the double block, but instead of the radii of the smaller and larger blocks, the radius of the drum and the length of the spoke must be taken, respectively, counting from the axis to the point of application of the force. Since the length of the spokes can be made many times greater than the radius of the drum, the gate makes it possible to balance forces many times greater than those applied to the spokes.
Problem No. 61
Is it possible to stretch a rope horizontally so that it does not sag?
Answer: It is forbidden. The forces of gravity and the tension of the rope are perpendicular to each other and cannot be balanced.
Problem No. 62
Why does a tightly stretched clothesline often break under the weight of a dress hung on it, while a loosely stretched one can withstand the same load?
Problem No. 63
For what purpose do circus performers hold heavy poles in their hands when walking on a tightrope?
Answer: The center of gravity of the man-pole system in equilibrium is located approximately at the middle of the pole above the rope. When a person moves along a rope, the displacement of the pole maintains this position of the system’s center of gravity (the pole moves to the left if the person leans to the right).
Semiradsky Heinrich Ippolitovich(October 24, 1843–08/23/1902) - Russian painter of Polish origin, one of the largest representatives of late academicism. He is best known for his monumental paintings on subjects from the history of ancient Greece and Rome.
Problem No. 64
A wire rod is suspended by a thread from the middle. Will it remain in balance if one end is bent in half?
Answer: No. From the side of the bent half of the rod, half the moment of force acts, since the center of gravity of this half has moved twice closer to the axis of rotation.
Problem No. 65
A stick hangs horizontally from a rope loop. One end of the stick is much thicker than the other. Let's cut the stick in the place where the loop was. Are the resulting parts of the stick the same weight?
Answer: The thick end of the stick weighs more.
Problem No. 66
A regular truncated pyramid rests on its large base. Will the center of gravity move relative to the pyramid if it is placed on a smaller base?
Answer: The center of gravity of the pyramid will not change its position relative to the pyramid itself, but will move relative to the plane of the support.
Problem No. 67
Sometimes examples of inclined bodies standing in equilibrium on a horizontal plane are "leaning towers". Why are these examples not considered appropriate for this case?
Answer: These towers are integral with the foundations buried in the ground. Therefore, the conditions for their equilibrium are different than for bodies resting on a horizontal surface.
For the curious:
The leaning Nevyansk Tower is an architectural pearl of the Urals.
It was built in the first half of the 18th century by order Akinfia Demidova, founder of the mining industry in Altai, son of a Tula industrialist Nikita Demidov. According to folk legends, it was originally planned this way - Akinfiy Demidov ordered the tower to be slightly tilted towards his native Tula;-)
Historians, local historians and architects are still arguing about the tilt of the tower. Some of them claim that Nevyansk Leaning Tower is an analogue leaning tower of pisa(it is known that the Demidovs visited Italy more than once at the beginning of the 18th century and planned to erect a tower in the Urals no worse than the Leaning Tower of Pisa). Local historians always clarify that the Nevyansk Tower, unlike the Pisa sister, does not fall, but is only tilted. There is a difference, of course: we don’t need to be saved ;-)
Efremov Alexey Valentinovich– modern Russian painter, graphic artist. Member of the Union of Artists of Russia.
Nevyansk- a city located on the eastern slope of the Ural ridge on the Neiva River, 99 km north of Yekaterinburg, 50 km south of Nizhny Tagil.
The angle of inclination of the Nevyansk Tower, according to estimates by various experts, ranges from eighty meters to two twenty centimeters. It is easy to verify that the angle of inclination does not change by carefully looking at the very top of the tower - there is a 25-kilogram weather vane installed there, which constantly rotates, indicating the direction of the wind. If the tower tilted even a little, the weather vane, according to the laws of physics, would stop rotating.
Secrets of the Nevyansk Tower
a clock with chimes, a lightning rod, a “hearing room”...
Chimes, installed on the Nevyansk Tower, were purchased by Akinfiy Demidov in England. The inscription on the chimes' bells reads: "Richard Phelpsi Lonpini Fecit 1730", which translated from Latin means: "Richard Phelpsi, made in London, 1730". Nevyansk craftsmen improved the English invention: on the largest alarm bell there is an inscription: “Summer 1732 June 1st this bell of the Nevyansk nobleman Akinfey Demidov factories. Weight 65 poods 27 pounds.” A few years later, the Nevyansk plant already had watch machines, “which cut wheels for watches and prepare other parts.” In the middle of the 18th century, “table and tower clocks” were manufactured here not only for the Demidov factories, but also for sale. The Nevyansk bells became famous throughout Siberia for their ringing...
But... the chimes on the Nevyansk Tower did not stand the test of time and remained silent for many years... The hands and clock mechanism broke, the musical shaft was twisted, the bells were covered with dust and oxides. There are traces of 2186 pins left on the shaft. Once upon a time, each peg in a certain sequence clung to levers, which were connected by strings to the hammers on the bells. But in what order exactly? How many melodies are encoded on the shaft? All these secrets in 1976 figured it out Soviet Ural master Alexander Sakantsev– a welding equipment adjuster, and a watchmaker by vocation. He restored the clock and the music machine. It was possible to decipher most of the melodies recorded on the musical shaft. These were English marches, folk songs of the 17th century, the melody was later recorded “Glory” - fragment from Mikhail Glinka’s opera “Ivan Susanin”. This is what the chimes are currently playing.
Akinfiy Nikitich Demidov
Georg Christoph Groot
before 1745
And also ;-)
Ural craftsmen built a 40-centimeter ball with spikes on the roof of the Nevyansk tower - the world's first lightning rod, that is, about a quarter of a century earlier than the American Benjamin Franklin demonstrated this invention.
Between the 4th and 5th floors in the Nevyansk tower there is "hearing room". A word spoken in a whisper in one corner is clearly heard in another, opposite corner. At the same time, neither in the center of the room nor at any other point what was said was completely audible. The Demidovs used this remarkable acoustic effect to eavesdrop on their workers and visiting auditors.
And that’s not all... Shrouded Nevyansk Tower legends under the most flag-weathervane with the coat of arms of the Demidovs…
It may turn out that you will be lucky enough to unravel its secrets, going back centuries;-)
Georg Christoph Groot(Georg Christoph Grooth; 01/21/1716–09/28/1749) - portrait artist, one of two brothers, German painters, who connected their lives with Russia. From 1743 court artist in St. Petersburg. Author of exquisite portraits in the Rococo style.
Problem No. 68
Why, when laying the walls of buildings, do they ensure that they are strictly vertical?
Problem No. 69
One of those sitting in the boat stood up to his full height. How did the stability of the boat change?
Answer: The equilibrium became less stable as the center of gravity of the entire system moved upward.
Anton Dorf(Anton Laurids Johannes Dorph; 02/15/1831-01/12/1914) - Danish artist.
Garfish (arrowfish)– a schooling predatory fish with a narrow, highly elongated body.
I couldn’t resist the temptation and decided to accompany the painting “Catching a garfish with a seine. Early morning" additional question ;-)
What month sickle depicted in a painting by Anton Dorff - young or old?
§ A hint for solving this problem can be found on - how to remember reliably and accurately where which month is facing?
Problem No. 70
If you try to place a chicken egg on a horizontal table surface, it will certainly lie on its side. From what and to what type of equilibrium does the egg pass?
Problem No. 71
Why does the crane not tip towards the load being lifted? Why, without a load, does the crane not tip towards the counterweight?
Answer: The design of the crane is such that in any case, a vertical line drawn through the center of gravity will intersect the support area.
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Pimenov Yuri Ivanovich(1903–1977) – Soviet painter and graphic artist. People's Artist of the USSR. Laureate of Lenin and two Stalin prizes of the second degree.
Problem No. 72
Why should you not use a crane to lift a load with the cable in an oblique position?
Answer: The tension on the cable increases and it may break.
Problem No. 73
A uniform rectangular brick lies on an inclined plane. Which half of the brick, top or bottom, exerts more pressure on the inclined plane?
Answer: The lower half, because if you draw a vertical plane through the straight line lying between the brick and the inclined plane, through the center of the brick, it will divide the brick into two unequal parts, with the lower half being larger. The support area of both parts is the same.
Problem No. 74
Draw the system of forces acting on a soaring kite in a horizontal wind.
Laura Knight(Laura Knight; 08/04/1877–07/07/1970) - English artist, representative of post-impressionism in painting. Commander of the Order of the British Empire.
Problem No. 75
Let's plunge into childhood;-) - we solve riddles, but... we don't just solve them, we comment in detail on the operating principle of each instrument, guided by the laws of physics.
1. Two rings, two ends, carnations in the middle. (Scissors)
2. Two sisters swayed, sought the truth, and when they achieved it, they stopped. (Scales)
3. There is a handle, not a rake; it digs the earth, not a plow. (Shovel)
4. He is thin, his head is as big as a pound, and as soon as he hits him, he will become strong. (Hammer)
5. A tenacious mouth is angry at those who sit on the board for nothing. (Pliers)
6. She eats quickly and chews finely, she does not swallow herself and does not give it to others. (Saw)
7. He rang in the forest all day
Thick, whitish from frost,
And at night, approaching the fire
He fell asleep with his nose buried in a log.
(Axe)
Answer to riddle number 7: Let's look at how an ax splits wood. Its blade is sharpened and widens closer to the base; the deeper the wedge of the ax is driven into the wood, the wider it spreads and eventually splits. The principle of operation of the wedge is the same as for the inclined plane. To move the pieces of wood apart a centimeter would require enormous force. It is enough to apply much less force to the wedge, although in this case you will have to make a greater movement deeper into the wood.
I wish you success in making your own decision
quality problems in physics!
I am very glad that the readers of the green pages liked my three wells puzzle. Thank you very much for your comments. I'm very pleased.
I hope you will enjoy another puzzle about a well, but not a simple well, but a very modernized one;-) Here is a painting by a German artist Felix Schlesinger "A Friend in Need". The picture shows manual wooden well pump. When the lever is raised and lowered, water is drained in portions through the pipe, the same one to which the girl pressed her lips when she wanted to get drunk. And now, attention, a question:
What is the design of a hand water pump?
Explain the operating sequence of this sophisticated unit.
In this case, simple mechanisms alone will not do the trick;-) you will have to remember about atmospheric pressure :-)
Invite the children to make a model of a hand pump for water. Drawings and drawings with explanations would be very appropriate in the accompanying documentation for the model. Announce a competition for the best model!!!
Despite all the delights of technological progress, hand pumps for water have not lost their attractiveness. And to this day they are very relevant in summer cottages and in the rural outback ;-) and not only in the Russian outback, but also in German, French, English... And for this reason, it will not be out of place if the guys prepare a detailed message on the topic “Types of hand pumps for water and features of their operation”.
Felix Schlesinger(Felix Schlesinger; 1833–1910) – German artist. Sergei Petrovich Tkachev(1922...) - Soviet and Russian painter, teacher, professor, veteran of the Great Patriotic War. Chairman of the Board of the Union of Artists of the RSFSR in 1976–1987. The elder brother of the People's Artist of the USSR, academician Alexei Petrovich Tkachev, with whom they form the creative tandem “The Tkachev Brothers”.
§ The Well Crane performed by Ivan Konstantinovich Aivazovsky on Literature:
§ Tulchinsky M.E. Qualitative problems in physics
Moscow: Prosveshchenie Publishing House, 1972
§ Demkovich V.P., Demkovich L.P. Collection of problems in physics
Moscow: Prosveshchenie Publishing House, 1981
§ Zolotov V.A. Questions and tasks in physics grades 6-7
Moscow: Prosveshchenie Publishing House, 1971
§ Katz Ts.B. Biophysics in physics lessons
Moscow: Prosveshchenie Publishing House, 1988
§ Perelman Ya.I. Do you know physics?
Domodedovo: publishing house "VAP", 1994