Lesson-generalization "simple mechanisms". Box of quality problems in physics: elements of statics, balance of bodies, moment of force, simple mechanisms...
"Examples of simple mechanisms" - The force that moves the body. Efficiency. The efficiency of some mechanisms. Inclined plane. Blocks. simple mechanisms. Lever rule. The use of a wedge when lifting weights. Wedge. Block. efficiency. Polyspast. Fixed block. moving block. Lever use. Lever arm. Leverage application. wedge application.
"Cam mechanism" - The most common are labial tubes. Video from the Polytechnic Museum. Reed pipes. Mechanical organ by Pavel Brugger (Moscow, 1880). Nurok with a programmed camshaft of a Brugger mechanical organ. Cam system and related mechanisms. On the monuments of science and technology of the Polytechnic Museum.
"Simple mechanisms Grade 7" - Project planning. Project planning: Control is carried out in several directions. Work in the computer science classroom after hours. Project summary. Project theme: "Simple mechanisms". The results are heard and discussed in class. In informatics, the project allows you to master Information Technology during the implementation of the project.
"Golden Rule of Mechanics" - Where a person uses simple mechanisms in his life. Tasks. What is called a simple mechanism. "Golden" rule of mechanics. Gate. Screw. Using a lever, we lifted the load to a height of 8 cm. How many times did we win in strength. The purpose of our lesson Block is a simple mechanism. Wedge. Inclined plane. Block.
"Simple mechanisms in everyday life" - Simple mechanisms. Sports sailing ships. A simple "inclined plane" mechanism. Means of siege. Systematize the acquired knowledge. Tower cranes. To get acquainted with the practical application of simple mechanisms. A simple "lever" mechanism. Piercing tools. Wedge. Simple mechanisms in nature.
"Using simple mechanisms" - Prepare a short message or presentation on the use of leverage. III option. Block. In wildlife. Arch of the foot. problem question: Think about whether it is possible to get a gain in work using a lever? living nature. Carpentry tools. On my way? Gate. Application in everyday life, technology and wildlife. In technology.
In total there are 8 presentations in the topic
v Topic of the lesson: "Simple mechanisms. Lever"
Archimedes.
The purpose of the lesson:
- to promote the development of the ability to analyze, put forward hypotheses, assumptions, make forecasts, observe and experiment; contribute to the development logical thinking; development of the ability to express in speech the results of one's own mental activity.
- awakening cognitive interest in the subject and surrounding phenomena; the formation of skills to critically, but objectively evaluate objects, phenomena, actions and actions (one's own and others'). computer, multimedia projector, screen, equipment for a mini-experiment (weights of 10 and 20 g, ruler, wooden stick), stick, weight, lever scales, tripod, demonstration lever, computer presentation of the lesson, Lego sets, computers for students .
During the classes:
(cartoon fragment)
Once along the seashore together Archimedes was walking with the king of Syracuse. The king said: - Your science is not easy ... - Trier was dragged aground by sailors. They pulled the ship, exhausted. And then Archimedes asked Hieron: - Do you remember my propeller for lifting water? In Egypt I made the work of the slaves easier. Do you know how a lever would help people
In hard work. For example, one would have managed on a sandy pier
I'll drag this trireme. - Hieron is standing, rubbing his temple: -Will you drag the trireme? One? On the sand?! - I will drag Trier ashore alone. Trier with rowers and cargo. Come here in a month...
We learned about it in Syracuse. At the appointed time, people gather On the pier, warmed by the sun. They look at the car, but do not expect a miracle: -Do not drag! Have you heard this!
I see ropes and a lot of wheels, And I am amazed at the size, But even Hercules, grabbing the cable, Will not drag the trireme onto the shore ... And then Archimedes turned the wheel - The trireme obediently crawls onto the sand. -Floats on the ground! the merchants shouted. And the guards were terrified. Rowers wave their oars through the air, As if they have lost their minds. I don't believe my eyes! How much strength in the shoulders?! No, king! This force was multiplied by the lever! - Archimedes looked: the sky, the sea all around. Blue sea and mountains. - I could turn the earth with a lever, just give me a fulcrum!
2 sl. 3 sl 4 sl
In front of you on the slide are stone statues on the coast of Easter Island in pacific ocean in the form of a human head up to 20 high and weighing 40-90 tons. How they were delivered to the coast is unknown - this is one of the main mysteries of the island, which has haunted several generations of travelers and explorers. According to legend, they "walked" themselves. A Norwegian traveler gives a description of one of these ways of moving statues, which was tested in action. local residents. So, one of the Moai, overturned from the pedestal, was hoisted back by using logs slipped under the statue, which resembled a lever in design.
5 sl Simple mechanisms are devices that serve to transform force. Simple mechanisms include: a lever and its varieties, a block and a gate, an inclined plane and its varieties, a wedge and a screw. We will consider the most common mechanism - the lever. 6 w 7 w
Take a toothpick and break it in half. Break the halves now. What is harder to break - a whole or a half? Why? 8 sl
10 sl 11 sl
I want to demonstrate to you the operation of a crane constructed from Lego blocks. The slide shows a real crane. 12 sl Why do cranes have counterweights? What can happen if the crane capacity is calculated incorrectly? Watch the video. 13 w.
14 sl
16 sl
As in any mechanism for the coupling of wagons, simple mechanisms are also used. I propose to evaluate my knowledge gained in the lesson using wagons different color: blue - I don’t understand the material well, green - I understand, but I still need to work, red - I understand everything, everything is working out. And draw your mood on the car in the form of a smiley. We collect the train on the board.
17 sl - extra.
View document content
"Development of a lesson in physics Simple mechanisms"
Lesson topic: "Simple mechanisms. Lever"
"Give me a foothold and I will lift the Earth!"
Archimedes.
The purpose of the lesson:
introduce students to various types simple mechanisms; consider simple mechanisms as devices that serve to transform power; consider the device and principle of operation of the lever; find out the equilibrium condition of the lever.
to promote the development of the ability to analyze, put forward hypotheses, assumptions, make forecasts, observe and experiment;
promote the development of logical thinking; development of the ability to express in speech the results of one's own mental activity.
awakening cognitive interest in the subject and surrounding phenomena; the formation of skills to critically, but objectively evaluate objects, phenomena, actions and actions (one's own and others').
Equipment and facilities for the educational process:
computer, multimedia projector, screen, equipment for a mini-experiment (weights of 10 and 20 g, ruler, wooden stick), stick, weight, lever scales, tripod, demonstration lever, computer presentation of the lesson, Lego sets, computers for students .
During the classes:
Preparation for the perception of new material.
(cartoon fragment)
Once upon a seashore together
Archimedes was walking with the king of Syracuse.
The king said: - Your sciences are not easy ... -
Trier was dragged aground by sailors.
They pulled the ship, exhausted.
And here Archimedes of Hiero asked:
- Do you remember my screw for lifting water?
In Egypt I made the work of the slaves easier.
Do you know how a lever would help people
In hard work. For example,
one would have managed on a sandy pier
I'll drag this trireme.-
Hieron is standing, rubbing his temple:
-Will you drag the trireme? One? On the sand?!
- I will drag Trier ashore alone.
Trier with rowers and cargo.
Come here in a month...
We learned about it in Syracuse ..
People gather at the appointed time
On the pier, warmed by the sun.
They look at the car, but do not expect a miracle:
-Do not pull! Have you heard this!
I see ropes and many wheels
And I marvel at the size
But even Hercules, grabbing the rope,
Will not drag a trireme ashore ...
And then Archimedes turned the wheel -
Trier obediently crawls onto the sand.
-Floats on the ground! the merchants shouted.
And the guards were terrified.
Rowers swing their oars through the air,
It's like they've lost their minds.
I don't believe my eyes! How much strength in the shoulders?!
No, king! This force was multiplied by the lever!-
Archimedes looked: the sky, the sea all around.
Blue sea and mountains.
- I could turn the earth with a lever,
just give me a foothold!
The word "Lever" sounded in the plot. Archimedes was going to turn the Earth with a lever, but what is a lever, what is its design and where is it used? (Student answers). You can give the exact answer to the questions posed at the end of our lesson, the topic of which is “Simple mechanisms.”. The motto of the lesson: "Give me a fulcrum, and I will lift the Earth!" 2 sl. 3 sl
4 sl
The physical capabilities of a person are limited, therefore, since ancient times, a person has often used devices that can transform a person’s strength into a much greater one. Such mechanisms are called "simple mechanisms". The first person to use simple mechanisms was our distant prehistoric ancestor, who moved heavy stones with a stick in search of edible roots or small animals hiding under the roots. There is a lot of evidence that in ancient countries - Babylon, Egypt, Greece - builders widely used simple mechanisms when lifting and transporting statues, columns and huge stones, in skillful hands a heavy load turned into a light one.
In front of you on the slide are Moai - stone statues on the coast of Easter Island in the Pacific Ocean in the form of a human head up to 20 meters high and weighing 40-90 tons. How they were delivered to the coast is unknown - this is one of the main mysteries of the island, which has haunted several generations of travelers and explorers. According to legend, they "walked" themselves. Norwegian traveler Thor Heyerdahl gives a description of one of these ways of moving statues, which was tested in action by local residents. So, one of the Moai, overturned from the pedestal, was hoisted back by using logs slipped under the statue, which resembled a lever in design.
What is a simple machine? What are simple mechanisms for?
5 sl
Simple machines are devices that serve to transform power. Simple mechanisms include: a lever and its varieties, a block and a gate, an inclined plane and its varieties, a wedge and a screw. We will consider the most common mechanism - the lever. 6 sl
7 w
Lever - is integral part almost every modern machine, machine tool, mechanism. The excavator digs a ditch - its iron "arm" with a bucket acts as a lever. The driver changes the speed of the car using the gearshift lever. Digging up beds in the garden, the shovel in our hands also becomes a lever. All kinds of rocker arms, handles and gates are all levers.
Let's find out how to use the lever correctly? (I ask two brave students to come to the board. I give one a heavy briefcase in his hands and suggest using a stick to facilitate the transfer of the load.) Show us how to place the stick on which the load weighs on the friend’s shoulder so that the pressure on the shoulder is the least ? A stick is a lever that we use to make it easier to carry a heavy load. How to hang the load on the lever?
Take a toothpick and break it in half. Break the halves now. What is harder to break - a whole or a half? Why? 8 sl
Lever arm - solid capable of rotating around a fixed support. In practice, a stick, board, crowbar, etc. can play the role of a lever.
The lever has a fulcrum and a shoulder. The shoulder is the shortest distance from the fulcrum to the line of action of the force (i.e., the perpendicular dropped from the fulcrum to the line of action of the force). Usually, the forces applied to the lever can be considered the weight of the bodies. One of the forces we will call the force of resistance, the other - the driving force.
What do you think will happen if one of the forces doubles? Answer: the scales will go out of balance (I show on ordinary scales). Do you think there is a way to balance the greater power with the lesser? Answer: yes, no. In the course of the experiment, I suggest that you derive the equilibrium condition for the lever.
Work with the computer model "Lever" (condition of equilibrium of the lever), the disk " Laboratory works in physics." Assignment to the computer model: hang the weights on the lever so that it is in balance. (If the first arm is 18 cm, a load with a gravity of 2N is hung from it, a load with a gravity of 3N is hung on the second arm, what is the length of the arm? 12 cm)
The lever is in equilibrium when the forces acting on it are inversely proportional to the shoulders of these forces. It is this rule of equilibrium of the lever that Archimedes deduced.
9 w. 3. Visual gymnastics.
Close your eyes and cover them with your palms. Imagine a sheet of white paper and try to mentally write your name on it in ink. If this succeeds, then spell your last name and patronymic, clearly imagining each letter separately. Put a period at the end of the entry. Now forget about the letters and remember only the dot. It should appear to you as moving from side to side in short, slow, light wiggles. You relax, remove your palms, open your eyes, we are returning to real world full of strength and energy.
10 sl
Today, simple mechanisms operate on cable cars, on drilling rigs, perform construction, installation and loading work. Tower cranes work at any construction site - this is a combination of levers, blocks, gates. Depending on the "specialty" cranes have different designs and characteristics. 11 sl
I want to demonstrate to you the operation of a crane constructed from Lego blocks. The slide shows a real crane.12 sl
Why do cranes have counterweights? What can happen if the crane capacity is calculated incorrectly?Watch the video.13 w.
Tasks: 1). On a board thrown over a log, 2 boys of different weights are swinging. Should they sit at the same distance from the support?
2). From the figure, determine what load should be placed at points A (2H), B (1H) and C (5H) so that it is in equilibrium? 14 sl
3). Why is the handle placed at the edge of the door?
Give examples of the use of levers in everyday life and technology.
Summarizing. Reflection. 15 sl
16 sl
As in any mechanism for the coupling of wagons, simple mechanisms are also used. I propose to evaluate my knowledge gained in the lesson using cars of different colors: blue - I do not understand the material well, green - I understand, but I still need to work, red - I understand everything, everything is working out. And draw your mood on the car in the form of a smiley. We collect the train on the board.
EFFECTIVENESS OF SIMPLE MECHANISMS Physics lessons in grade 7
CONTROL UNIT Answer the questions of the wise owl
Answer question 1. What is " Golden Rule» mechanics? 2. Do simple mechanisms give a gain in work? 3. Prove that the "golden rule" of mechanics applies to a hydraulic machine.
Answer question 4. Will any of the levers in the picture be in balance? F 1 F 2 F 1 F 1 F 1 F 2 F 2 F 2 1) 2) 3) 4)
Answer question 5. Which of the inclined planes do you think gives the greatest gain in strength? Why? 1) 2) 3) 1) 2) 3) a) b)
Answer question 7. Why is the door handle located not in the middle of the door, but closer to its edge? 6 . 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? 8. Why does a wing nut have blades?
Answer question 9. Why are scissors with short handles and long blades used for cutting paper and fabric, and long handled and short blades for cutting sheet metal? 10. In a school workshop, a boy, in order to strongly clamp the workpiece in a vice, is taken not by the middle, but by the edge of the handle? Why?
EFFICIENCY OF SIMPLE MECHANISMS Lesson topic:
WHAT SHOULD YOU KNOW? 1. What work is called useful, what is complete? 2. Why is the work done more than the useful work in practice? 3. What is the efficiency factor? four . Can the efficiency be greater than one? 5. How can efficiency be increased?
WHAT WORK IS USEFUL, WHAT IS COMPLETE? Assignment: A barrel weighing 200 kg must be lifted aboard the ship to a height of 10 m. Questions: 1. What work must be done to complete the task? A = F ∙ s = m ∙ g ∙ s = 200 kg ∙ 10 N/kg ∙ 10 m = 20,000 J 2. Why do loaders use an inclined plane? 3. What do loaders gain by using an inclined plane, and what do they lose? 4. Do loaders get a gain in work by using an inclined plane? 5. Did we take into account the action of friction and resistance forces when calculating the work? 6. Is it necessary in practice to do additional work to overcome the forces of friction and resistance? What work needs to be done in practice? In practice, the total work done by the mechanism Az is always somewhat greater than the useful work. Ap
EFFICIENCY COEFFICIENT (EFFICIENCY) The ratio of useful work to full work is called the efficiency of the mechanism Efficiency = Ap Az η = Ap Az ∙ 100% "this" The efficiency cannot be more than 1 (or 100%), because In practice, there are always forces of resistance.
HOW TO INCREASE EFFICIENCY? Lever Inclined plane Block Did we take into account when calculating the work: The weight of the lever? Hook weight? Friction? Friction between body and plane? block weight? Rope weight? Friction? To increase efficiency, it is necessary to reduce friction and use light but strong materials.
SOLVING THE PROBLEM A load of 100 kg is suspended on the short arm of the lever. To lift it, a force of 250 N was applied to the long arm. The load was lifted by 0.08 m, while the application point driving force dropped by 0.4 m. Find the efficiency of the lever. m = 100 kg g = 9.8 N/kg F = 250 N h 1 = 0.08 m h 2 = 0.4 m η = ? F h 1 h 2 η = Ap Az ∙ 100% A p = P ∙ h 1 A z = F ∙ h 2 η = m ∙ g ∙ h 1 F ∙ h 2 ∙ 100% [ η ] = [kg ∙ N ∙ m ∙ % P = m∙g N ∙ kg ∙ m = % ] η = 100 ∙ 10 ∙ 0.08 ∙ 100 250 ∙ 0.4 = 80% Answer: η = 80%
Strive to comprehend science ever deeper,
Longing for the knowledge of the eternal.
Only the first knowledge will flash you light,
You will know: there is no limit to knowledge.
Ferdowsi
Hakim Abulqasim Mansour Hassan Ferdowsi Tusi (935-1020) - Persian poet.
BOX OF QUALITATIVE TASKS IN PHYSICS: ELEMENTS OF STATICS
balance of bodies, moment of force, simple mechanisms...
Didactic materials in physics for students, as well as their parents ;-) and, of course, for creative teachers. For those who love to learn!
Your attention 75
quality problems in physics on the topic: "Elements of statics: balance of bodies, moment of force, simple mechanisms".
Let's accompany the tasks with informative notes and comments - for the curious we will give detailed answers to some tasks ;-) According to the tradition of green pages, we will treat ourselves masterpieces of world art…
And also ;-) let's get acquainted with some secrets inclined Nevyansk tower - an architectural gem of the Urals, shrouded in legends under the very flag-weather vane with the coat of arms of the Demidovs ...
Task #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 diagrams.
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; March 15, 1839–March 9, 1924) was an American genre painter.
Task #2
"Yamskaya Sloboda", 1927. Andrey Platonovich Platonov
“... In the middle of the settlement stood a two-story old house. There is a well near it, and near the well there is a round barn - a dungeon for a horse. In that dungeon all day the horse circled in a narrow place, dragging a wooden carrier. Ropes were twisted and untwisted on the carrier, which dragged water from the well in buckets. 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 market watered the horses a penny from the head, and people drank for free ... "
What simple mechanisms used to draw water from a well are referred to in this passage?
Task #3
What kind mechanical movements happen to different parts of the gate while using it?
Answer: Rotational (wheel, shaft) and translational (rope, lifted load - a bucket of water).
Task #4
Firefighters and climbers sometimes use a stationary simple block to lift themselves up a rope or cable. Does this result in a gain in strength in relation to the weight of the load being lifted?
Answer: It turns out a gain in strength twice.
I did not expect that the task number 4 "about firefighters and climbers" would cause such heated debate. Some of the comments are hidden (not deleted!) due to excessive aggression and confusion. In this case, apparently, it is worth analyzing the solution of this simple problem in more detail.
Taking this opportunity, I decided to add to the page a reproduction of the painting by Rostislav Vovkushevsky "Climbers". For some, just a picture, but for someone 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 fixed block does not give 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 a force half as much as his weight. Since in this case the weight of a person is distributed equally on two parts of the cable or rope (on opposite sides of the block).
F = P/2 = mg/2
It turns out a gain in strength twice.
At the same time, 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 power, we lose on the way". This proposition is so general and at the same time so important that it has been called "golden rule" of mechanics.
It turns out that we have achieved a double gain in strength at the cost of a double loss along the way. In other words, in order to lift oneself with the help of a fixed block, say, to a height of 15 meters, a person must, sorting through 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:
Gained a double win ;-)
Received a double loss on the way.
Didn't get any win :-(
We are not talking about work in the condition of problem No. 4 “about firefighters and climbers”, but for the sake of completeness, let it be ... Apparently, those who stirred you up do not catch the difference between strength and work ...
Task #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) was an English genre painter.
Task #6
Why is a screwdriver made with a thickened handle?
Answer: The large diameter of the handle increases the leverage of the force applied by us in order to be able to reduce this force. For the same reason, the key to the door is always made with a wide part in the place of holding by hand, 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 corkscrew tip into the depth of the cork, which without this rotation would require a lot of force. The same principle as in the lever is used in the pliers...
Task #7
Why is it easier to cut thick cardboard with the middle of scissors than with their ends?
Answer: This makes it possible to reduce the force applied to the handles of the scissors.
Task #8
Stationery scissors have very long blades. Is it profitable?
Answer: The loss in strength is not significant here, and the gain in speed is of great importance.
Johan August Malmström(Johan August Malmström; 10/14/1829–10/18/1901) was a Swedish genre painter.
Task #9
Why is the product sometimes pushed out of the scissors when cutting?
Answer: The resultant of the forces acting on the cut object from the side of the scissors blade is not equal to 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 the Celtic tribes. They were two knives connected by an arcuate springy metal plate. Similar scissors are still used today for shearing sheep. Modern type scissors (two articulated knives) appeared around the 8th century AD in the Middle East. In Russia, the oldest articulated scissors were found in the Gnezdovsky barrows - an archaeological reserve in Smolensk region Russia (the settlement of Gnezdovo was most likely founded at the beginning of the 10th century).
Task #10
Where is the handle placed on the door to make it easier to open the door?
Answer: The handle is placed at the edge of the door to increase the leverage and thus facilitate the opening of the door.
Task #11
Why is it easier to climb a gentle staircase than a steep one?
Task #12
Why do roads in mountainous areas zigzag?
(06/06/1844 - 02/13/1905) - Russian genre painter, academician, full member of the Imperial Academy of Arts, member of the Association of Traveling Art Exhibitions, teacher.
Auvergne- an administrative region of France, located on the territory of the Central mountain range. The highest peak is Mount Sancy (1886 m). Auvergne is rich in mineral waters and thermal springs.
Task #13
What simple mechanisms underlie the work of tools and devices that workers use in the construction of the road in the painting by Joseph Vernet?
Claude Joseph Vernet(Claude Joseph Vernet; 08/14/1714 - 12/03/1789) - French painter.
Task #14
Why the presence of significant rises in the area railway necessitates the use of higher power locomotives?
Task #15
Why do train drivers avoid stopping trains on the rise?
Task #16
What is the easiest way to move a railway car: applying force to the body of the car or to the top of the wheel rim?
Answer: In the second case, half the force is required, since the instantaneous axis of rotation of the wheel passes through the point of contact with the rail.
Task #17
Why doesn't a single-rail suspension railway car tip over?
Answer: The center of gravity of the wagon is below the suspension line.
Task #18
If a fast moving car brakes sharply, then its front end drops down. Why?
Probably soon we will forget how to walk
Already the habit of driving lives in us
To walk just two steps we suffer
A hundred kilometers by car does not count
Cars, cars literally filled everything
Where the age-old dust lay
The car has left its mark...
"Cars"- song of the Soviet ensemble "Funny boys", 1987
words: Michael Shabrov, music: Vladimir Matecki.
Alan Fearnley(Alan Fearnley) - British artist, master of "automobile" painting.
Task #19
Why do cars, bicycles, etc. Is it better to put the brakes on the rear rather than the front wheels?
Answer: In order not to create overturning the car in a vertical plane and turning it in a horizontal plane, the moments of forces that may occur when braking the front wheels.
Task #20
To pull out a stuck car, use the following technique. A long strong rope is tightly tied to a tree or stump near the road and to the car so that the rope is taut. Then pull the middle of the rope at a right angle in its direction. What is this approach based on?
Answer: The reception is based on a huge gain in strength on the cable with a large angle between the component forces.
Task #21
Consider simple mechanisms whose principles are used in a bicycle (steering wheel, pedal, gear). In which of them do they achieve a gain in strength, and in which - a gain in speed?
Task #22
At what position of the bicycle pedal will the moment of the force acting on it, directed vertically, be the greatest? 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 - 12/5/1926) - French landscape painter, one of the founders of impressionism.
Task #23
A person, in order not to slip on an icy hill, runs away from it. Why is it advisable?
Task #24
Why do people walk on slippery ice with small steps?
Answer: On ice, the friction force is small, and with large steps, a person leans heavily. As a result, the moment of gravity may not be compensated by the moment of friction and the person will fall.
Task #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 tending to rotate his body around a vertical axis. Therefore, the skater, in time with the movement of the legs, swings his arms in such a way that, by the movement of his arms, he creates moments of forces that counteract the moments of forces due to the movement of the legs and compensate for them.
Task #26
A shovel is a well-known garden tool for digging up the soil. What simple mechanism is used in this wonderful tool? 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 coast of the Adriatic Sea.
Problem #27
Why can a bent arm lift more weight than an outstretched arm?
Answer: Reducing the lever arm makes it possible to increase the weight of the lifted load.
Task #28
Explain the operation of the human hand and foot using the rule of leverage.
Problem #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.
Task #30
Do you need to spread your legs wide apart when lifting heavy weights, or should they be kept together?
Answer: It is necessary, since the center of mass of a person who spreads his legs wide is lower and he is more stable.
Task #31
Rocker - a wooden device used to facilitate the carrying of two buckets of water, buckets, baskets ... and other loads. What is the benefit 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 wrote in the style of academic classicism.
Task #32
The load is carried on a stick slung over the shoulder. How does the position of the load (closer or farther from the shoulder) affect the amount of force with which the stick acts on the shoulder, and the force with which the hand must keep 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 pressure force of the stick on the shoulder, equal to the sum of the weight of the load and the force of the arm, will be less.
Task #33
Why does a person carrying a heavy suitcase or bag in one hand lean in the opposite direction?
Problem #34
Why does a person carrying a heavy load on his back lean forward?
Answer: To position the center of gravity of your body with the load on the support area.
Julien Dupre(Julien Dupre; 03/19/1851 - 04/15/1910) - French artist, representative of realism.
Problem #35
Why can't you get up from a chair without tilting your body forward?
Answer: If you do not tilt the body forward, then the vertical drawn through the center of gravity of a person will not cross the area of \u200b\u200bsupport (feet).
Task #36
Why is it easier to cut meat not just by pressing on the knife, but by pressing and moving the knife back and forth?
Answer: When the knife moves, its “cutting section” is not a section perpendicular to the cutting edge, as in 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 greater the speed of the knife.
Problem #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 sharpening it 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) was a Polish realist painter.
Problem #38
Why are hacksaws with small teeth used for sawing hard metal, and large teeth for sawing soft metal?
Problem #39
It is easier to hold a long rod in a horizontal position by the middle than by the end. Why?
Answer: If you keep the rod in the middle, then you do not need to apply a moment of force to keep the rod in balance. If you hold on to one of the ends, then you need to apply a moment of force.
Task #40
When a stick is held in the hands by the ends, it is difficult to break it. If the middle of the stick is placed on a stand, then it is easier to break the stick. Explain why.
Task #41
Break a thin piece of wood in half, break the resulting pieces into two parts again, and so on. Why does breaking get harder every time?
Answer: The shoulders of the forces applied to the chip are reduced.
Task #42
Explain how a catapult works. What simple mechanism works in it key role? Where are catapults currently used?
Edward John Pointer(Edward John Poynter; 1836-1919) - English painter.
Catapult- the Greek term for any throwing machine.
For the curious: The principle of operation of the catapult. Unlike a bow, where kinetic energy is provided by the elasticity of the bent arms of the bow, in catapults and ballistas, energy is stored in twisted bundles (bundles) of low-elastic fibers. The lever, inserted at one end into a twisted bundle, tends to unwind, accelerating the other end of the lever to high speed. In this way each arm of the catapult consists of a horizontal arm inserted into a tourniquet twisted with a certain force, as well as bases or frames where the tourniquet is vertically attached. Both arms of the catapult are connected by a bowstring, which can only be pulled back with 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 shells and aircraft from aircraft carriers. Developments are underway to create catapults for launching cargo spaceships from the surface of the planets.
Task #43
In what case will a barrel rolled on inclined bars produce more pressure on them at the same height: when are they longer or shorter?
Answer: With longer bars.
Task #44
A wheelbarrow is a simple device, consisting of a cargo body, wheels and handles, and designed to transport 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 wheel of a wheelbarrow (which in this case plays the role of the axis of the lever) than the force acting from the hands of a person. Therefore, a person can lift such a load on a wheelbarrow that he is not able to lift directly with his hands. The force acting from the hands of a person must be directed upwards 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 - 02/13/1905) - Russian genre painter, academician, full member of the Imperial Academy of Arts, member of the Association of Traveling Art Exhibitions, teacher.
Problem #45
Why is it impossible to make sure by means of a balance that the force of gravity changes with the transition from the equator to the poles?
Answer: Since two forces equal to gravity are balanced on the lever. A change in one of them occurs simultaneously with a change in the other.
Task #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 side to the other? Accompany your answer with a picture.
Problem #47
There are two cast iron plates of the same mass. One slab is twice as long as the other. Both slabs are lifted by the edge with a turn near the rib forming the width of the slab and placed vertically. Which plate requires the most force to lift?
Answer: The force is required to be applied the same, equal to half the gravity of the plate.
Problem #48
Levers that are used "in reverse";-) Leverage is not always used to do work with less force. Sometimes it is important to win in the movement, even if it means applying a lot of force. So does the fisherman who needs to pull the fish, move it a long distance. At the same time, he uses a fishing rod as a lever. Comment on the above using a schematic drawing.
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 #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 of different materials, are balanced on the lever, and one weight is 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 pull.
Problem #51
Two cast-iron weights of the same mass are suspended from an equal-armed lever on threads. Will the balance of the lever change if one of them is immersed in water and the other in oil?
Answer: It will change: the weight in the oil will fall, and in the water it will rise.
Problem #52
Porcelain balls are suspended from an equal-arm lever. If one of the balls is lowered into a glass of water, and the other is lowered into a glass of kerosene, then the lever is in equilibrium. Will the balance be disturbed if the vessels with liquids are removed?
Answer: Yes, it will pull the ball that was in the water.
Problem #53
Explain what a balance scale is. What is the basis for the work of these scales?
Answer: Rocker scales are an equal-arm lever (rocker), to both ends of which are suspended bowls for weights and the load to be weighed. In an equal-arm lever, the support is located at an equal distance from the points of application of forces. The basis of the operation of such scales is the principle of balance.
Leon Augustine Lhermitte(Leon Augustin Lhermitte; 07/31/1844 - 07/28/1925) - French genre painter, engraver.
I suggest that readers of green pages 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 Alma-Ata
Problem #54
On the one hand, a brass one was hung from the balance beam, and on the other - equal mass cast iron weight. Will the balance remain in equilibrium if it is lowered so that both weights are in the water?
Answer: The brass weight will pull.
Problem #55
How, without using scales, to determine the mass of the ruler using a weight of known mass? Do it.
Answer: It is necessary to hang the weight from one end of the ruler and place the ruler on a point support so that it is in balance. From the equation of moments we find the mass of the ruler.
Problem #56
As you know, a fixed block does not give a gain in strength. However, when checking with a dynamometer, it turns out that the force holding the load on a fixed block is slightly less than the gravity of the load, and with a uniform rise it is greater than it. What explains this?
Answer: The action of the force of friction.
Problem #57
Why is a heavy load attached to the middle part of the cable connecting the tug and the barge during stormy weather?
Answer: To avoid excessive cable tension.
Problem #58
What will happen if the rowers sitting in the boat, depicted in the painting by Vasily Surikov “Stepan Razin”, start moving the oars in opposite directions?
Answer: The boat will start turning.
Surikov Vasily Ivanovich(01/24/1848 - 03/19/1916) - Russian painter, master of large-scale historical canvases.
Problem #59
The ship has two engines. How will the ship move if the command is given: “The right engine is full forward, the left engine is full back!”? The thrust forces of both engines are the same modulo.
Answer: Rotate under the action of a pair of forces counterclockwise.
Problem #60
What device is depicted in Henry Bacon's painting "Towing a Ship"? Explain how it works.
Henry Bacon(Henry Bacon; 839-1912) was an American painter.
Answer: The picture of Henry Bacon "Towing a ship" depicts capstan(vertical gate - a modified double block), used to pull up ships at the berths, as well as to select ship anchors. The spokes of the capstan play the same role as the larger diameter pulley in the double pulley. 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 should be taken, respectively, counting from the axis to the place where the force is applied. Since the length of the spokes can be made many times greater than the radius of the drum, the collar makes it possible to balance forces many times greater than those applied to the spokes.
Problem #61
Is it possible to stretch the 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 balance.
Problem #62
Why does a taut clothesline often break under the weight of a dress hung on it, while a loosely taut one can withstand the same load?
Problem #63
Why do circus performers hold heavy poles in their hands when walking on a tightrope?
Answer: The center of gravity of the system man - pole in equilibrium is located approximately at the middle of the pole above the rope. When a person moves along the rope, this position of the center of gravity of the system is maintained by the displacement of the pole (the pole moves to the left if the person leans to the right).
Semiradsky Genrikh Ippolitovich(10/24/1843 - 08/23/1902) - Russian painter of Polish origin, one of the largest representatives of late academicism. He is best known for his monumental paintings depicting scenes from the history of ancient Greece and Rome.
Problem #64
A rod of wire is suspended from a thread in the middle. Will it stay 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 as close to the axis of rotation.
Problem #65
A stick hangs on a rope loop in a horizontal position. One end of the stick is much thicker than the other. Cut the stick where the loop was. Is the weight of the resulting parts of the stick the same?
Answer: The thick end of the stick weighs more.
Problem #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 support plane.
Problem #67
Sometimes, as examples of inclined bodies standing in equilibrium on a horizontal plane, they give "falling towers". Why can't these examples be considered appropriate for this case?
Answer: These towers are one 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:
Leaning Nevyansk Tower - an architectural gem of the Urals.
It was built in the first half of the 18th century by order of Akinfia Demidova, the founder of the mining industry in Altai, the son of a Tula industrialist Nikita Demidov. According to folk legends, it was originally planned like this - 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 Leaning Tower of Nevyansk is an analogue leaning tower of pisa(it is known that the Demidovs visited Italy more than once in early XVIII century and decided to put a tower in the Urals no worse than the Leaning Tower). Local historians are sure to clarify that the Nevyansk Tower, unlike the Leaning sister of Pisa, does not fall, but is only tilted. Of course, there is a difference: ours does not need to be saved ;-)
Efremov Alexey Valentinovich- contemporary Russian painter, graphic artist. Member of the Union of Artists of Russia.
Nevyansk- a city located on the eastern slope of the Ural Range 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 the calculations of various experts, is from eighty meters to two meters and 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 - a 25-kilogram weather vane is installed there, which constantly rotates, indicating the direction of the wind. If the tower tilted just a little bit, the weather vane, according to the laws of physics, would stop rotating.
Secrets of the Nevyansk Tower
clock with chimes, lightning rod, "auditory room" ...
chimes, installed on the Nevyansk tower, were bought by Akinfiy Demidov in England. On the bells of the chimes, the inscription has been preserved: "Richard Phelpsi Lonpini Fecit 1730", which in Latin means: "Richard Phelps, made in London, 1730". The Nevyansk craftsmen perfected the English invention: on the largest alarm bell there is an inscription: “Summer 1732 June 1, this bell of the Nevyansk nobleman Akinfey Demidov was cast in the factories. Weight 65 pounds 27 pounds. A few years later, the Nevyansk factory already had watch machines, “which cut through the wheels for the clock and prepare other parts.” In the middle of the 18th century, “table and tower clocks” were made here not only for the Demidov factories, but also for sale. Nevyansk bells became famous for their ringing throughout Siberia ...
But ... the chimes on the Nevyansk tower did not stand the test of time and were silent for many years ... The arrows and the clockwork broke, the musical shaft was mangled, the bells were covered with dust and oxides. There were traces of 2186 pegs on the shaft. Once upon a time, each peg in a certain sequence clung to the levers, which were connected by strings to the hammers on the bells. But in what order? How many melodies are encoded on the shaft? All these secrets in 1976 unraveled Soviet Ural master Alexander Sakantsev- adjuster of welding equipment, and by calling a watchmaker. He restored the clock and the musical machine. Managed to decipher most melodies recorded on a musical shaft. These were English marches, folk songs of the 17th century, later a melody was recorded "Glory" - a fragment from Mikhail Glinka's opera "Ivan Susanin". It is she who is currently playing the chimes.
Akinfiy Nikitich Demidov
Georg Christoph Groot
before 1745
And more ;-)
Ural craftsmen built a 40-cm spiked ball on the roof of the Nevyansk Tower - 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 is located "auditory room". A word whispered in one corner is clearly audible in another, opposite corner. At the same time, neither in the center of the room, nor at any other point, what was said is completely inaudible. The Demidovs used this wonderful acoustic effect to eavesdrop on their working and visiting auditors.
And that's not all... Shrouded Nevyansk tower legends under the most weather vane flag with the coat of arms of the Demidovs…
It may turn out that it is you who will be lucky enough to unravel its secrets, going back centuries ;-)
Georg Christoph Groot(Georg Christoph Grooth; 01/21/1716 - 09/28/1749) - portrait painter, one of two brothers, German painters who connected their lives with Russia. Since 1743 he was a court painter in St. Petersburg. The author of exquisite portraits in the Rococo style.
Problem #68
Why, when laying the walls of buildings, are they made to be strictly vertical?
Problem #69
One of those sitting in the boat stood up to his full height. How did this change the stability of the boat?
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) was a Danish painter.
Garfish (arrow fish)- schooling predatory fish with a narrow strongly elongated body.
I could not resist the temptation and decided to accompany the painting “Catching a garfish with a net. Early morning" additional question ;-)
Sickle of what month depicted in a painting by Anton Dorf - young or old?
§ A hint for solving this problem can be found on - how to remember reliably and accurately, where which month looks?
Problem #70
If you try to put a chicken egg on a horizontal surface of the table, then it will certainly lie on its side. From what and to what type of equilibrium does the egg pass in this case?
Problem #71
Why does the crane not tip towards the load being lifted? Why does the crane not tip towards the counterweight without a load?
Answer: The design of the crane is such that in any case, the vertical drawn through the center of gravity will cross the support area.
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Pimenov Yury Ivanovich(1903-1977) - Soviet painter and graphic artist. People's Artist of the USSR. Winner of the Lenin and two Stalin Prizes of the second degree.
Problem #72
Why should not a crane be used to lift a load with an oblique position of the cable?
Answer: The tensile strength of the cable increases and it may break.
Problem #73
A homogeneous 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 a straight line lying between the brick and the inclined plane, through the center of the brick, then it will divide the brick into two unequal parts, with the lower half being larger. The area of support of both parts is the same.
Problem #74
Draw a system of forces acting on a hovering 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 #75
We plunge into childhood ;-) - solve riddles, but ... not just solve, but comment in detail on the principle of operation of each tool, guided by the laws of physics.
1. Two rings, two ends, carnations in the middle. (Scissors)
2. Two sisters rocked, they sought the truth, and when they achieved it, they stopped. (Scales)
3. There is a handle, not a rake, it digs the ground, not a plow. (Shovel)
4. He himself is thin, his head is a pood, as he hits, he will become strong. (A hammer)
5. A tenacious mouth is angry at those who sit in vain on the board. (pincers)
6. He eats quickly and chews finely, does not swallow himself and does not give to others. (Saw)
7. He rang in the forest all day
Thick, whitish from hoarfrost,
And at night, going up to the fire
He fell asleep with his nose buried in a log.
(Axe)
Answer to riddle number 7: Consider how an ax splits wood. Its blade is pointed and expands closer to the base, the deeper the wedge of the ax is driven into the wood, the wider it is distributed and eventually splits. The principle of operation of the wedge is the same as for the inclined plane. To push the pieces of wood a centimeter, you would need to apply a huge force. It is enough to apply a much smaller force to the wedge, although in this case you will have to make a greater movement deep into the wood.
I wish you success in your decision
quality problems in physics!
I am very glad that the readers of the green pages liked my puzzle about three wells. Thank you very much for your comments. I'm very pleased.
I hope you will like it another problem about the 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 is a friend". 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 who wants to get drunk clung to her lips. And now, attention, a question:
What is the device of a manual water pump?
Explain the sequence of operation of this tricky unit.
In this case, the matter will not do with simple mechanisms alone ;-) you will have to remember about atmospheric pressure :-)
Invite the children to make a model of a hand pump for water. In the accompanying documentation for the model, drawings and drawings with explanations will be very appropriate. Announce a contest for the best model!!!
Despite all the charms technical progress, hand pumps for water have not lost their appeal. 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 therefore it will not be superfluous if the guys prepare a detailed message on the topic "Varieties of hand pumps for water and features of their work".
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. Older brother folk artist USSR, academician Alexei Petrovich Tkachev, with whom they make up the creative tandem "The Tkachev Brothers".
§ Well crane performed by Ivan Konstantinovich Aivazovsky on Literature:
§ Tulchinsky M.E. Qualitative tasks in physics
Moscow: Enlightenment publishing house, 1972
§ Demkovich V.P., Demkovich L.P. Collection of problems in physics
Moscow: Enlightenment publishing house, 1981
§ Zolotov V.A. Questions and tasks in physics grade 6-7
Moscow: Enlightenment publishing house, 1971
§ Katz Ts.B. Biophysics at physics lessons
Moscow: Enlightenment publishing house, 1988
§ Perelman Ya.I. Do you know physics?
Domodedovo: VAP publishing house, 1994