Размышляя topic simple machines. Методическая разработка занятия по английскому языку на тему "Машины и работа" (3 курс)

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    You"re watching FreeSchool! Hi everyone! Today we"re going to talk about simple machines. A simple machine is a device that makes work easier by magnifying or changing the direction of a force. That means that simple machines allow someone to do the same work with less effort! Simple machines have been known since prehistoric times and were used to help build the amazing structures left behind by ancient cultures. The Greek philosopher Archimedes identified three simple machines more than 2,000 years ago: the lever, the pulley, and the screw. He discovered that a lever would create a mechanical advantage, which means that using a lever would allow a person to move something that would normally be too heavy for them to shift. Archimedes said that with a long enough lever and a place to rest it, a person could move the world. Over the next few centuries more simple machines were recognized but it was less than 450 years ago that the last of the simple machines, the inclined plane, was identified. There are six types of simple machines: the Lever, the Wheel and Axle, the Pulley, the Inclined plane, the Wedge, and the Screw. Pulleys and Wheel and Axles are both a type of Lever. Wedges and Screws are both types of Inclined Planes. Each type of Simple Machine has a specific purpose and way they help do work. When speaking of simple machines, "work" means using energy to move an object across a distance. The further you have to move the object, the more energy it takes to move it. Let"s see how each type of simple machine helps do work. A LEVER is a tool like a bar or rod that sits and turns on a fixed support called a fulcrum. When you use a lever, you apply a small force over a long distance, and the lever converts it to a larger force over a shorter distance. Some examples of levers are seesaws, crowbars, and tweezers. A Wheel and Axle is easy to recognize. It consists of a wheel with a rod in the middle. You probably already know that it"s easier to move something heavy if you can put it in something with wheels, but you might not know why. For one thing, using wheels reduces the friction - or resistance between surfaces - between the load and the ground. Secondly, much like the lever, a smaller force applied to the rim of the wheel is converted to a larger force traveling a smaller distance at the axle. Wheel and axles are used for machines such as cars, bicycles, and scooters, but they are also used in other ways, like doorknobs and pencil sharpeners. A Pulley is a machine that uses a wheel with a rope wrapped around it. The wheel often has a groove in it, which the rope fits into. One end of the rope goes around the load, and the other end is where you apply the force. Pulleys can be used to move loads or change the direction of the force you are using, and help make work easier by allowing you to spread a weaker force out along a longer path to accomplish a job. By linking multiple pulleys together, you can do the same job with even less force, because you are applying the force along a much longer distance. Pulleys may be used to raise and lower flags, blinds, or sails, and are used to help raise and lower elevators. An Inclined Plane is a flat surface with one end higher than the other. Inclined planes allow loads to slide up to a higher level instead of being lifted, which allows the work to be accomplished with a smaller force spread over a longer distance. You may recognize an inclined plane as the simple machine used in ramps and slides. A Wedge is simply two inclined planes placed back to back. It is used to push two objects apart. A smaller force applied to the back of the wedge is converted to a greater force in a small area at the tip of the wedge. Examples of wedges are axes, knives, and chisels. A Screw is basically an inclined plane wrapped around a pole. Screws can be used to hold things together or to lift things. Just like the inclined plane, the longer the path the force takes, the less force is required to do the work. Screws with more threads take less force to do a job since the force has to travel a longer distance. Examples of screws are screws, nuts, bolts, jar lids, and lightbulbs. These six simple machines can be combined to form compound or complex machines, and are considered by some to be the foundation of all machinery. For example, a wheelbarrow is made of levers combined with a wheel and axle. A pair of scissors is another complex machine: the two blades are wedges, but they are connected by a lever that allows them to come together and cut. We use simple machines to help us do work every day. Every time you open a door or a bottle, cut up your food, or even just climb stairs, you are using simple machines. Take a look and see if you can identify the simple machines around you and figure out how they make it easier to do work.

    Contents

History

The idea of a simple machine originated with the Greek philosopher Archimedes around the 3rd century BC, who studied the Archimedean simple machines: lever, pulley, and screw . He discovered the principle of mechanical advantage in the lever. Archimedes" famous remark with regard to the lever: "Give me a place to stand on, and I will move the Earth." (Greek : δῶς μοι πᾶ στῶ καὶ τὰν γᾶν κινάσω ) expresses his realization that there was no limit to the amount of force amplification that could be achieved by using mechanical advantage. Later Greek philosophers defined the classic five simple machines (excluding the inclined plane) and were able to roughly calculate their mechanical advantage. For example, Heron of Alexandria (ca. 10–75 AD) in his work Mechanics lists five mechanisms that can "set a load in motion"; lever , windlass , pulley , wedge , and screw , and describes their fabrication and uses. However the Greeks" understanding was limited to the statics of simple machines; the balance of forces, and did not include dynamics ; the tradeoff between force and distance, or the concept of work .

Frictionless analysis

Although each machine works differently mechanically, the way they function is similar mathematically. In each machine, a force F in {\displaystyle F_{\text{in}}\,} is applied to the device at one point, and it does work moving a load, F out {\displaystyle F_{\text{out}}\,} at another point. Although some machines only change the direction of the force, such as a stationary pulley, most machines multiply the magnitude of the force by a factor, the mechanical advantage

M A = F out / F in {\displaystyle \mathrm {MA} =F_{\text{out}}/F_{\text{in}}\,}

that can be calculated from the machine"s geometry and friction.

The mechanical advantage can be greater or less than one:

  • The most common example is a screw. In most screws, applying torque to the shaft can cause it to turn, moving the shaft linearly to do work against a load, but no amount of axial load force against the shaft will cause it to turn backwards.
  • In an inclined plane, a load can be pulled up the plane by a sideways input force, but if the plane is not too steep and there is enough friction between load and plane, when the input force is removed the load will remain motionless and will not slide down the plane, regardless of its weight.
  • A wedge can be driven into a block of wood by force on the end, such as from hitting it with a sledge hammer, forcing the sides apart, but no amount of compression force from the wood walls will cause it to pop back out of the block.

A machine will be self-locking if and only if its efficiency η is below 50%:

η ≡ F o u t / F i n d i n / d o u t < 0.50 {\displaystyle \eta \equiv {\frac {F_{out}/F_{in}}{d_{in}/d_{out}}}<0.50\,}

Whether a machine is self-locking depends on both the friction forces (coefficient of static friction) between its parts, and the distance ratio d in /d out (ideal mechanical advantage). If both the friction and ideal mechanical advantage are high enough, it will self-lock.

Proof

When a machine moves in the forward direction from point 1 to point 2, with the input force doing work on a load force, from conservation of energy the input work W 1,2 {\displaystyle W_{\text{1,2}}\,} is equal to the sum of the work done on the load force W load {\displaystyle W_{\text{load}}\,} and the work lost to friction

W 1,2 = W load + W fric (1) {\displaystyle W_{\text{1,2}}=W_{\text{load}}+W_{\text{fric}}\qquad \qquad (1)\,}

If the efficiency is below 50% η = W load / W 1,2 < 1 / 2 {\displaystyle \eta =W_{\text{load}}/W_{\text{1,2}}<1/2\,}

2 W load < W 1,2 {\displaystyle 2W_{\text{load}} 2 W load < W load + W fric {\displaystyle 2W_{\text{load}} W load < W fric {\displaystyle W_{\text{load}}

When the machine moves backward from point 2 to point 1 with the load force doing work on the input force, the work lost to friction W fric {\displaystyle W_{\text{fric}}\,} is the same

W load = W 2,1 + W fric {\displaystyle W_{\text{load}}=W_{\text{2,1}}+W_{\text{fric}}\,}

So the output work is

W 2,1 = W load − W fric < 0 {\displaystyle W_{\text{2,1}}=W_{\text{load}}-W_{\text{fric}}<0\,}

Thus the machine self-locks, because the work dissipated in friction is greater than the work done by the load force moving it backwards even with no input force

Modern machine theory

Kinematic chains

Classification of machines

The identification of simple machines arises from a desire for a systematic method to invent new machines. Therefore, an important concern is how simple machines are combined to make more complex machines. One approach is to attach simple machines in series to obtain compound machines.

However, a more successful strategy was identified by Franz Reuleaux , who collected and studied over 800 elementary machines. He realized that a lever, pulley, and wheel and axle are in essence the same device: a body rotating about a hinge. Similarly, an inclined plane, wedge, and screw are a block sliding on a flat surface.

This realization shows that it is the joints, or the connections that provide movement, that are the primary elements of a machine. Starting with four types of joints, the revolute joint , sliding joint , cam joint and gear joint , and related connections such as cables and belts, it is possible to understand a machine as an assembly of solid parts that connect these joints.

See also

References

  1. Chambers, Ephraim (1728), "Table of Mechanicks", Cyclopædia, A Useful Dictionary of Arts and Sciences , London, England, Volume 2, p. 528, Plate 11 .
  2. Paul, Akshoy; Roy, Pijush; Mukherjee, Sanchayan (2005), Mechanical sciences: engineering mechanics and strength of materials , Prentice Hall of India, p. 215, ISBN .
  3. ^ Asimov, Isaac (1988), Understanding Physics , New York, New York, USA: Barnes & Noble, p. 88, ISBN .
  4. Anderson, William Ballantyne (1914). Physics for Technical Students: Mechanics and Heat . New York, USA: McGraw Hill. pp. 112–122. Retrieved 2008-05-11 .
  5. ^ Compound machines , University of Virginia Physics Department, retrieved 2010-06-11 .
  6. ^ Usher, Abbott Payson (1988). A History of Mechanical Inventions . USA: Courier Dover Publications. p. 98. ISBN .
  7. Wallenstein, Andrew (June 2002). . Proceedings of the 9th Annual Workshop on the Design, Specification, and Verification of Interactive Systems . Springer. p. 136. Retrieved 2008-05-21 .
  8. ^ Prater, Edward L. (1994), Basic machines (PDF) , U.S. Navy Naval Education and Training Professional Development and Technology Center, NAVEDTRA 14037.
  9. U.S. Navy Bureau of Naval Personnel (1971), Basic machines and how they work (PDF) , Dover Publications.
  10. Reuleaux, F. (1963) , The kinematics of machinery (translated and annotated by A.B.W. Kennedy) , New York, New York, USA: reprinted by Dover.
  11. Cornell University , Reuleaux Collection of Mechanisms and Machines at Cornell University , Cornell University.
  12. ^ Chiu, Y. C. (2010), An introduction to the History of Project Management , Delft: Eburon Academic Publishers, p. 42,

How Simple Machines Work

What is a simple machine and how do they work? I"m so glad you asked! Machines make work easier by changing the size of force, direction of force, or distance the force acts on.

Lifting a car with a flat tire and loosening the lugnuts can be accomplished by a single person thanks to simple machines. The jack and lug wrench are simple machines that alter the force needed to change the tire.

Six Simple Machines

Simple machines are basic devices used to alter the force needed to accomplish a task. There are six types of simple machines.

  • lever
  • wheel and axle
  • inclined plane
  • wedge
  • screw
  • pulley

The first type of simple machine is the lever. A lever is a rigid bar that rotates on the fixed point of a fulcrum and changes the distance or size of a force.

There are three classes of levers. A first class lever has an input force and output force on either side of the fulcrum. This causes the output to move in the opposite direction of the the input force. An example of a first class lever is a see-saw. A second class lever has an output force between the input force and fulcrum. This changes the distance of the force. A wheelbarrow is a second class lever. The third class lever has the input force between the output and fulcrum. A broom is a third class lever.

Wheel and Axle

The wheel and axle make work easier by changing the distance the force acts on. A wheel and axle consists of two disks or

cylinders with different radiuses. Examples are a steering wheel and shaft, a car wheel and axle, and a screwdriver.

Inclined Plane

An inclined plane is a slanted surface on which a force can move an object to a different elevation. Why do gentler slopes and ramps require less energy to move a load on? Because the input force required to travel the greater distance of a slope is changed to the smaller distance of the output force – the upward motion.

A wedge is a device made of two back to back inclined planes and is used to split objects. When a wedge is driven into a log, the size of the input force at the wider top of the wedge is changed to greater output force at the narrower point forcing the wedge through the wood. Knife blades are an example of a wedge.

A screw is an inclined plane wrapped around a cylinder. Screws with threads closer together require

less force to turn because the length of the inclined plane is longer. Nuts and bolts are screws. A nut is a screw with the threads on the inside.

The last type of simple machine is the pulley. A pulley consists of a rope that fits into a groove in a wheel. A pulley makes work easier by changing the direction or direction and size of the force.

There are three types of pulleys . They are the fixed pulley, moveable pulley and pulley system.

The fixed pulley is a single fixed pulley and rope. This changes the output direction of the force, making it opposite of the input. When you pull down on a fixed pulley a weight is lifted up.

A moveable pulley is fixed to the object being moved instead of a fixed location. Moveable pulleys multiply the input force needed to lift a heavy object thus reducing the force needed to lift heavy objects. Moveable pulleys are used to move ship sails and window washer platforms.

Pulley systems combine fixed and moveable pulleys to create large mechanical advantages. A crane uses pulley systems to lift enormous loads like locomotives.

References

  • Michael Wysession, David Frank, Sophia Yancopoulos. Physical Science Concepts in Action. p.417 – 435. New Jersey: Prentice Hall, 2004.

Or . However, some of the most important and useful machines are quite simple. In fact, scientists even call them simple machines!

So what is a simple machine? Is it a machine that does a simple , such as addition or ? Maybe it"s just a machine that"s really easy to operate, like an old television remote control? Or could it be any machine that makes life easier?

While simple machines do make our lives easier, they"re much older than either television remotes or calculators. Simple machines are some of the first machines ever created.

Since the earliest human beings walked on Earth, they looked for ways to make the of everyday life easier to accomplish. Over time, they did this by inventing what has become known as the six simple machines.

Wedges are moving inclined planes used to lift or separate. Wedges are usually used to cut, tear, or break an object into pieces. Common wedges include knives, axes, saws, scissors, and shovels. However, wedges can also be used to hold things in place, such as in the case of staples, nails, shims, or doorstops.

A is a twisted version of an inclined plane. It allows movement to be translated into an up or down motion that takes up less space. Screws can also help hold things together. Common examples of screws include jar lids, drills, light bulbs, and bottle caps.

These six simple machines are all around us. Often more machines, also called machines, consist of one or more of the simple machines put together. Can you imagine how much easier life became after the invention of these simple machines?

(15 minutes)
  • Distribute small toy cars that have wheels joined by axles to groups of students. Kick-start a discussion with some questions about the toy car mechanics, such as: How do these toy cars move? How are the wheels on each side of the car joined to each other?
  • Have a student volunteer point to the rod that holds the two wheels together. Explain that the bar that joins two wheels is called an axle .
  • Tell students that they will be learning about wheels and axles.
  • Hold up the doorknob, explaining that it is an everyday example of a wheel and axle.
  • Challenge the students to help you identify the wheel and axle in the doorknob. Listen as different students call out their guesses.
  • After some speculation, tell students that the knob that turns is the wheel. The inner rod that is attached to the knob is the axle.
  • Demonstrate how the wheel and axle works by turning the knob (wheel). That turns the inner rod (axle) and moves the latch, to open the door.

Guided Practice

(15 minutes)
  • To consolidate student thinking, set up activity stations with play dough and a rolling pin.
  • Let students practice flattening the dough with the pin.
  • Guide them to express these understandings: The rolling pin is a wheel and axle. When you push on the handles (the axle) the wheel turns and flattens out the dough.
  • Challenge students to think of other common machines that have one wheel like the rolling pin. Great examples include a wheelbarrow, a top, and a playground merry-go-round.

Independent working time

(15 minutes)
  • Pass out a copy of the Wheel and Axle worksheet to each student to complete independently.
  • Walk around the classroom to offer support to students who get stuck.

Differentiation

  • Enrichment: Have students who need more of a challenge read a history of other simple machines, and fill out an accompanying word search.
  • Support: Put students who need more support into pairs to complete the Wheel and Axle worksheet.

Assessment

(10 minutes)
  • Collect the worksheets that the students have filled out, and correct them using the Wheel and Axle answer sheet.

Review and closing

(5 minutes)
  • In summary, remind students that the rolling pin is a wheel and axle. When you push on the handles (the axle) the wheel turns and flattens out the dough.
  • Challenge students to think of other common machines that have one wheel like the rolling pin, such as a wheelbarrow, top, and merry-go-round.
  • Remind your class that the wheel and axle is only one of six common simple machines that help things move. For homework or additional independent work, consider encouraging students to learn more about other kinds of simple machines.

Topic: Simple Machines PSSA: 3.4.7.C / S8.C.3.1

Objective: TLW compare different types of simple machines. TLW compare different types of simple machines. TLW explain the difference between a simple machine and a compound machine. TLW explain the difference between a simple machine and a compound machine.

MI #1: Levers A lever is a simple machine that has a bar that pivots on a fixed point called a fulcrum. A lever is a simple machine that has a bar that pivots on a fixed point called a fulcrum. Levers are classified based on the location of the input force, load, and the fulcrum. Levers are classified based on the location of the input force, load, and the fulcrum.

MI #2: Classes of Levers First class levers have the fulcrum between the input force and the load. First class levers have the fulcrum between the input force and the load. - Includes see-saws Second class levers have the load between the input force and the fulcrum. Second class levers have the load between the input force and the fulcrum. - Includes wheelbarrows Third class levers have the input force between the load and the fulcrum. Third class levers have the input force between the load and the fulcrum. - Includes hammers and fishing poles

Mi #3: Pulleys A pulley is a simple machine that has a grooved wheel that holds a rope or a chain. A pulley is a simple machine that has a grooved wheel that holds a rope or a chain. There are three types of pulleys; fixed, movable, and block and tackle. There are three types of pulleys; fixed, movable, and block and tackle.

MI #4: Wheel and Axle A wheel and axle consists of two circular objects of different sizes that rotate on the same axis. A wheel and axle consists of two circular objects of different sizes that rotate on the same axis. The axle rotates a smaller distance than the wheel, which results in a greater output force. The axle rotates a smaller distance than the wheel, which results in a greater output force.

MI #5: Inclined Planes An inclined plane is a straight slanted surface. An inclined plane is a straight slanted surface. A wedge is a pair of inclined planes that move. A wedge is a pair of inclined planes that move. A screw is an inclined plane wrapped around a cylinder. A screw is an inclined plane wrapped around a cylinder.

MI #6: Compound Machines A compound machine is a machine that is made of two or more simple machines working together. A compound machine is a machine that is made of two or more simple machines working together. Because compound machines have more moving parts, their mechanical efficiency is typically low. Because compound machines have more moving parts, their mechanical efficiency is typically low.

So What…? Real Life Application Machines make work easier, so it is important to understand the different types of simple machines. Machines make work easier, so it is important to understand the different types of simple machines.

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