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_____ ______ _____ _________
SIMPLE MECHANISMS
COMPLETED:
MOU "Secondary School with. Agafonovka, St. Petersburg District, Saratov Region"
Head: Dzyurich E.A.
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physical dictionary
A mechanism is a tool, a structure. - Block - from the English word block - part of the lifting mechanism, tool, structure. - Machine - from the Latin word machina - a structure in the form of a wheel with a chute around the circumference.
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History reference
The first simplest machines (lever, wedge, wheel, inclined plane, etc.) appeared in antiquity. The first tool of man - a stick - is a lever. A stone ax is a combination of a lever and a wedge. The wheel appeared in the Bronze Age. Somewhat later, an inclined plane began to be used. Already in the 5th century BC. in the Athenian army (Peloponessian War), wall-beating machines (rams), throwing devices (ballistae and catapults) were used. The construction of dams, bridges, pyramids, ships and other structures, as well as handicraft production, on the one hand, contributed to the accumulation of knowledge about mechanical phenomena, and on the other hand, required new knowledge.
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ABOUT THE EGYPTIAN PYRAMIDS
The Egyptian pyramids are the tombs of the pharaohs, the kings of Ancient Egypt. The construction of the pyramids was carried out approximately from 2700 to 1800. BC. Each pharaoh, having ascended the throne, began to build a pyramid in which, after death, he should be buried. And the more powerful and richer the pharaoh was, the more majestic was his tomb. The total mass of stone blocks, processed and laid in pyramids, was calculated - 6.5 million tons.
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HYPOTHESIS ABOUT CONSTRUCTION OF THE PYRAMID
Builders could use a helix-shaped plane of brick. Such an inclined plane requires much less material. It could be erected around the pyramid close to its edges, gradually rising up with it. It has non-abundances. The spiral embankment and scaffolding will overlap and take up all the free space long before reaching the top, and the corners will be the most difficult place in the entire structure to overcome.
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About the secrets of the construction of the pyramids
It has been proven that the construction technique of antiquity made it possible to erect such monumental structures. Limestone blocks were cut down in quarries and processed on the spot - hewn and polished with copper tools. The stone was finished so carefully that in the future the blocks fit snugly against each other. Masters achieved amazing results - and a millennium later, even a thread cannot be pulled between the faces of neighboring plates. Then multi-ton blocks, using drag skids and simple levers, were loaded on a barge during the flood period along specially dug channels and sent to the construction site.
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The process of erecting the pyramid was simple, but laborious. Clay mortar was used for masonry. Blocks were lifted to the upper rows of masonry along inclined embankments built of raw bricks. The remains of such mounds were found in Medum and Giza, near the pyramids of the pharaohs Huni and Khafre. They pulled the blocks on the rope with copper hooks. Perhaps the sled was also used. In a word, the main secret of the pyramids is the diligence and talent of a person.
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Archimedes was born in Syracuse on the island of Sicily in 287. BC. Archimedes began his creative activity as an engineer, creating various mechanical devices that were widely used in construction and everyday life. In total, about forty inventions are attributed to Archimedes, including the propeller and the chain hoist.
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How the Greeks moved heavy loads
The experience of Egypt, where the pharaohs drove thousands of slaves to build the pyramids, was inapplicable in Greece. A way out was found: a column, attached in a special way to a wooden frame, was, as it were, turned into a stone skating rink. And rolling weights is much easier than dragging. For rectangular blocks, Metagen came up with a different method: each block, like an axle, was inserted into huge wooden wheels with a diameter of about 4 meters and rolled to the construction site. To lift loads, the Greeks invented cranes, consisting of blocks, ropes and ladders. The Temple of Artemis at Ephesus (built around 550 BC) was one of the most beautiful and famous creations of Greek architecture and was considered the third wonder of the world. During the construction of the temple, the construction managers of Hersi-fron and Metagen faced a difficult problem: how to transport heavy columns and blocks from the quarry to the place of work on loose soil?
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Leverage in wildlife
In the skeleton of animals and humans, all bones that have some freedom of movement are levers. For example, in a person - the bones of the arms and legs, the lower jaw, the skull, the finger. In cats, movable claws are levers; many fish have spines on the dorsal fin; in arthropods, most segments of their external skeleton; bivalve mollusks have shell valves. Skeletal linkages are primarily designed to gain speed with a loss in strength. Especially large gains in speed are obtained in insects.
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Polyspast
Pay attention to the chain hoist - a combination of n blocks loosely put on a common axle. Usually, two chain hoists are used in technology - fixed and movable, - a load of weight P = Ft is suspended from the axis of the latter. The gain in strength in this case is 2n, since the blocks act independently of each other. The force is distributed equally between the blocks Ft / n and is halved with each block. As a result, we get F = Fт/2n. Of course, the gain in strength is compensated by the same loss in distance - we do not win in work. The invention of the chain hoist is attributed to Archimedes.
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Used Books:
Balashov M.M. Physics. - M .: Education, 1994. Golin G.M., Filonovich S.R. Classics of physical science (from ancient times to the beginning of the 20th century). - M .: Higher School, 1989. Katz Ts.B. Biophysics at the lessons of physics. - M .: Education, 1988 Perelman Ya.I. Entertaining physics: Book 1.- M .: Science 1979. Encyclopedia for children: T. 14 - "Technique". - M .: Avanta +, 2000. I know the world: Children's encyclopedia "The world of the mysterious." – M.: Astrel, 2004.
Review questions:
1. What is strength?
2. What forces do you know?
3. What is the name of the device for measuring force?
4. What is called work in physics?
5. What is the working formula?
6. In what units is work measured?
7. What is power?
8. What is the power formula?
9. In what units is power measured?
Riddle 1:
I will believe with a long neck,
I will pick up a heavy load,
Where they order, I will put
I serve the man.
Riddle 2:
Wonderful buddy: wooden hand
Yes, an iron butt, a hardened comb.
He is held in high esteem by carpenters, every day with him at work.
Riddle 3:
Toothy, not biting.
Riddle 4:
Looks, we opened our mouths,
You can put paper in it:
Paper in our mouth
Will be divided into parts.
Riddle 5:
Two brothers went into the water to swim, two are swimming, and one is lying on the shore.
Riddle 6:
They stuffed her mouth with meat
And she chews it
Chewing, chewing and not swallowing -
Sends to the plate.
Riddle 7
Bucket loudly, descending, jumping,
And rising - creaks and cries.
In a deep mine, water is stored,
So that in the sultry summer you can get drunk.
Riddle 8
He himself is thin, and his head is a pood.
simple mechanisms
Prepared by: physics teacher
MBOU "Secondary School No. 13 of the city of Evpatoria" Shvaiko L.A.
simple mechanisms
Since time immemorial, people have used various devices to perform mechanical work. With the help of levers 3 thousand. years ago, during the construction of the pyramid of Cheops in ancient Egypt, they moved and lifted slabs weighing 2.5 tons to a height of 147 meters.
Simple mechanisms are called devices that serve to transform power.
Simple mechanisms include: a lever and its varieties - a block, a gate; inclined plane and its varieties - wedge, screw.
In most cases, simple mechanisms are used in order to obtain a gain in strength, i.e., to increase the force acting on the body by several times.
simple mechanisms
Inclined plane
fixed
mobile
Task number 1 "Strongman"
Can a person hold 5 tons of weight? Can you crush iron with your hand? Can a child resist a strongman? What mechanism can be used to do this?
The lever is a rigid body that can rotate around a fixed support.
Point O is the fulcrum, located between the points of application of forces.
The shortest distance between the fulcrum and the straight line along which the force acts on the lever is called the arm of the force.
Lever equilibrium condition
The lever is in equilibrium when the forces acting on it are inversely proportional to the shoulders of these forces.
Task #1:
Vertical forces of 2 and 18 N are applied to the ends of the horizontal lever, which is in equilibrium. What is the gain in leverage?
Task number 2 "Builder"
How to raise a covering for it on the roof of a 9-storey building? What mechanisms can be used to do this?
Block is a wheel with a groove, reinforced in the holder. A rope, cable or chain is passed along the gutter of the block.
Fixed block - a block, the axis of which is fixed and does not rise or fall when lifting loads .
OA \u003d R \u003d arm of force F 1
OB \u003d R \u003d arm of force F 2
OB = 2R= force arm F
OA \u003d R \u003d arm of the force P
The movable block gives a gain in strength of 2 times.
F 1 s 1 = F 2 s 2
Task #2:
With the help of a movable block, the load was lifted to a height of 1.5 m, to what length was the free end of the rope extended?
In order to lift the load to a height h with the help of a movable block, it is necessary to move the end of the rope to which the dynamometer is attached to a height of 2 h=2∙1.5=3 m.
Task #3:
The worker, with the help of a movable block, lifted the load to a height of 7 m, applying a force of 160 N to the free end of the rope. What work did he do?
Task number 3 "Trickster"
How to lift a barrel of nails onto a truck body without a crane and other lifting machines? How to divide an oak chock into two parts? How is water pumped out of ships that have received a hole? What mechanisms can be used to do this?
Task #4:
The cart is lifted along an inclined plane, the length of which is 3 m and the height is 1.5 m. Find the gain in the force of the inclined plane?
Tasks for self-control:
1. What are the names of devices that serve to transform power?
2. What simple mechanisms are used in everyday life?
3. What simple mechanisms were used in Egypt to build the pyramids?
4. What is the name of a rigid body that can rotate around a fixed axis?
5. What is the name of the shortest distance between the fulcrum and the straight line along which the force acts on the lever?
6. Write down the balance condition of the lever as a formula.
7. By whom was this rule established?
8. What is the purpose of the fixed block?
9. For what purpose is the movable block used?
10. Why is the handle placed at the edge of the door?
Homework:
- Fill in the table:
Application of simple mechanisms
in the animal kingdom
in vegetable
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simple mechanisms
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There are situations when you have to lift some heavy object, such as a cabinet. Often, human power is not enough for this. But it doesn't matter: you can slip a strong stick under the edge of the cabinet, and the cabinet will be raised without much difficulty.
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It is not always possible to crush the nut shell. And this is not a problem - there are special nutcrackers, with their help you can easily cope with this task. If a person does not have enough strength to do this or that work, he picks up some kind of device, and overwhelming work immediately becomes on his shoulder.
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Simple mechanisms (Greek "mehane" - machine, tool) are devices that serve to transform power. In most cases, simple mechanisms are used in order to obtain a gain in strength, i.e., to increase the force acting on the body by several times.
Block
gate
Lever arm
Inclined plane
Wedge
Screw
simple mechanisms
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A lever is a rigid body that can rotate around a fixed support. The wheel is also a lever, since it is a rigid body rotating around an axis.
Lever arm
The line of action of a force is a straight line passing through the force vector. The shortest distance from the axis of the lever to the line of action of the force is called the arm of the force.
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In the figure on the left, the lever is the pedal. Its axis of rotation passes through point O. Two forces are applied to the pedal: F1 is the force with which the foot presses on the pedal and F2 is the elastic force of the stretched cable attached to the pedal. Drawing through the vector F1 the line of action of the force (shown in blue) and lowering the perpendicular from point O onto it, we get the segment OA - the arm of the force F1. With the force F2, the situation is even simpler: its line of action can be omitted, since the vector of this force is located more successfully. Lowering from t. O the perpendicular to the line of action of the force F2, we get the segment OB - 2 arm of this force.
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The lever is in equilibrium when the forces acting on it are inversely proportional to the shoulders of these forces.
For the first lever, the lever of the left force is 2 times greater than the shoulder of the right force, therefore, the right force is twice as large as the left force. For the second lever, the leverage of the right force is 1.5 times greater than the leverage of the left force, that is, the same number of times as the left force is greater than the right force. So, when two forces are in equilibrium on the lever, the larger of them always has a smaller leverage and vice versa.
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With the help of a lever, a small force can balance a large force. Consider, for example, lifting a bucket from a well. The lever is a well gate - a log with a curved handle attached to it. The axis of rotation of the gate passes through the log. The lesser force is the force of the person's hand, and the greater force is the force with which the bucket and the hanging part of the chain are pulled down.
Gate.
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Block
Block - simple mechanical device, which allows you to change the force. The fixed block has a fixed axis and is designed to redirect force. The fixed block is used to lift small loads or to change the direction of force. Does not give a gain in strength.
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The movable block has a free axle and is designed to convert forces (to lift larger loads than the previous one). Changes the direction of the force. In the absence of friction forces, it gives a gain in strength by a factor of 2.
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Rolling barrels down an inclined plane, people apply less force than if they were lifting barrels on ropes. In other words, the forces applied by people are less than the weight of the barrels. In the absence of friction forces, the inclined plane gives a gain in force as many times as the length is greater than the height of the inclined plane.
Inclined plane
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A wedge is a variation of a simple mechanism called an inclined plane. It is used to obtain a gain in strength, that is, with the help of a smaller force to counteract a larger force.
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The screw is the second kind of inclined plane. By turning the corkscrew handle clockwise, we cause the corkscrew screw to move down. In other words, there is a transformation of movement: the rotational movement of the corkscrew leads to its forward movement.
Slide 14
Acting on the long arm of the force, we gain in strength, but at the same time we lose in distance by the same factor, therefore, when using simple mechanisms, we cannot win in work, since the product of the force F and the path s is work. The work performed by the forces applied to a simple mechanism are equal to each other: F1s1=F2s2 A1=A2
The "golden rule" of mechanics
The presentation was developed based on the book by Ts.B. Katz "Biophysics at the lessons of physics". I have been using the material in this book in physics classes for many years. With the advent of the computer, I continue to tell children about the connections between physics and biology, while using ICT tools.
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Slides captions:
Simple mechanisms The work of a physics teacher MKOU "Lipetsk school" Novoduginsky district of the Smolensk region Sarioglo Nadezhda Nikolaevna
Human strength is limited! Simple mechanisms are devices (devices) that allow you to convert force into a force that is significantly greater. Simple mechanisms give a gain in strength.
Lever A lever is a rigid body that can rotate around a fixed point of support. The equilibrium condition for a lever is:
Block A block is a wheel with a groove around the circumference for a rope or chain. Blocks are used in lifting devices. Fixed block Movable block Changes direction of force There is NO gain in force!!! Balanced lever. P=F P F P F=P/2 Gains in power by 2 times. Miscellaneous lever. F
P= 600 N 3 movable blocks 3 fixed blocks F= 100 N Pulley block - a combination of several movable and fixed blocks (poly - a lot, spao - pull) Gain in strength - 6 times!!!
Gate A gate is two wheels connected together and rotating around the same axis, for example, a well gate with a handle
Inclined plane - a simple mechanism in the form of a flat surface set at an angle other than a straight one to a horizontal surface
A screw is a simple machine. The thread of the screw is an inclined plane wrapped around the cylinder many times
A wedge is a simple mechanism in the form of a prism, the working surfaces of which converge at an acute angle. Used for moving apart, dividing into parts of the processed object
In the skeleton of animals and humans, all bones that have some freedom of movement are levers. . One-shoulder lever of the human hand Levers of the forelimb of the dog Simple mechanisms in wildlife
In humans, the levers are the bones of the limbs, the lower jaw, the skull (the fulcrum is the first vertebra), the phalanges of the fingers. Pulling force of muscles and ligaments attached to the occipital bone Gravity of the head An example of the operation of a lever - the action of the arch of the foot when lifting on the toes Simple mechanisms in wildlife
In cats, levers are movable claws In arthropods, most segments of their external skeleton Simple mechanisms in wildlife
In many fish, the spines of the dorsal fin are simple mechanisms Simple mechanisms in wildlife
In bivalve mollusks, shell valves are simple mechanisms. Simple mechanisms in wildlife
The short legs of the mole are designed to develop large forces at low speed. Simple mechanisms in wildlife
The long legs of the greyhound and deer determine their ability to run fast. Simple mechanisms in wildlife
The long jaws of the greyhound allow you to quickly grab prey on the run. The short jaws of the bulldog close slowly, but hold strongly. Simple mechanisms in wildlife
Link mechanisms can be found in sage flowers Long lever arm Short lever arm guards the entrance to the flower Simple mechanisms in wildlife
The "piercing tools" of many animals and plants resemble a wedge in shape. Simple mechanisms in wildlife
The pointed shape of the head of fast-moving fish is also similar to a wedge. Simple mechanisms in wildlife
Simple mechanisms in everyday life Application of the equilibrium condition of the lever when working with a wheelbarrow
Simple mechanisms in everyday life Applying the equilibrium condition of the lever, it is easier for the first person to carry the load if it is closer to the shoulder
Simple mechanisms in everyday life Libra is an equal-armed lever
Simple mechanisms in everyday life
Simple mechanisms in engineering
Simple mechanisms in engineering Fire engine with an arrow - an example of a lever
Simple mechanisms in engineering Tower cranes are used in the construction of high-rise buildings
1. Katz Ts.B. Biophysics at physics lessons. - M. Enlightenment, 1988.- 160s. 2. Katz Ts.B. Physics and Live nature. - Physics at school. - 1995. - No. 2 and No. 3. 3. Internet - resources. Literature
