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

So the output work is

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.

UXL Encyclopedia of Science
COPYRIGHT 2002 The Gale Group, Inc.

Machines, simple

A simple machine is a device for doing work that has only one part. Simple machines redirect or change the size of forces, allowing people to do work with less muscle effort and greater speed, thus making their work easier. There are six kinds of simple machines: the lever, the pulley, the wheel and axle , the inclined plane , the wedge, and the screw.

Everyday work

We all do work in our daily lives and we all use simple machines every day. Work as defined by science is force acting upon an object in order to move it across a distance. So scientifically, whenever we push, pull, or cause something to move by using a force, we are performing work. A machine is basically a tool used to make this work easier, and a simple machine is among the simplest tools we can use. Therefore, from a scientific standpoint, we are doing work when we open a can of paint with a screwdriver, use a spade to pull out weeds, slide boxes down a ramp, or go up and down on a see-saw. In each of these examples we are using a simple machine that allows us to achieve our goal with less muscle effort or in a shorter amount of time.

Earliest simple machines

This idea of doing something in a better or easier way or of using less of our own muscle power has always been a goal of humans. Probably from the beginning of human history, anyone who ever had a job to do would eventually look for a way to do it better, quicker, and easier. Most people try to make a physical job easier rather than harder to do. In fact, one of our human predecessors is called Homo habilis, which means "handy man" or "capable man." This early version of our human ancestors was given that name because, although not quite fully human, it had a large enough brain to understand the idea of a tool, as well as hands with fingers and thumbs that were capable of making and using a tool. Therefore, the first simple machine was probably a strong stick (the lever) that our ancestor used to move a heavy object, or perhaps it was a sharp rock (the wedge) used to scrape an animal skin, or something else equally simple but effective. Other early examples might be a rolling log, which is a primitive form of the wheel and axle , and a sloping hill, which is a natural inclined plane . There is evidence throughout all early civilizations that humans used simple machines to satisfy their needs and to modify their environment.

Words to Know

Compound machine: A machine consisting of two or more simple machines.

Effort force: The force applied to a machine.

Fulcrum: The point or support on which a lever turns.

Resistance force: The force exerted by a machine.

Work: Transfer of energy by a force acting to move matter.

The beauty of simple machines is seen in the way they are used as extensions of our own muscles, as well as in how they can redirect or magnify the strength and force of an individual. They do this by increasing the efficiency of our work, as well as by what is called a mechanical advantage. A mechanical advantage occurs when a simple machine takes a small "input" force (our own muscle power) and increases the magnitude of the "output" force. A good example of this is when a person uses a small input force on a jack handle and produces an output force large enough to easily lift one end of an automobile. The efficiency and advantage produced by such a simple device can be amazing, and it was with such simple machines that the rock statues of Easter Island , the stone pillars of Stonehenge, and the Great Pyramids of Egypt were constructed. Some of the known accomplishments of these early users of simple machines are truly amazing. For example, we have evidence that the builders of the pyramids moved limestone blocks weighing between 2 and 70 tons (1.8 and 63.5 metric tons) hundreds of miles, and that they built ramps over 1 mile (1.6 kilometers) long.

Trade-offs of simple machines

One of the keys to understanding how a simple machine makes things easier is to realize that the amount of work a machine can do is equal to the force used, multiplied by the distance that the machine moves or lifts the object. In other words, we can multiply the force we are able to exert if we increase the distance. For example, the longer the inclined plane— which is basically a ramp— the smaller the force needed to move an object. Picture having to lift a heavy box straight up off the ground and place it on a high self. If the box is too heavy for us to pick up, we can build a ramp (an inclined plane) and push it up. Common sense tells us that the steeper (or shorter) the ramp, the harder it is to push the object to the top. Yet the longer (and less steep) it is, the easier it is to move the box, little by little. Therefore, if we are not in a hurry (like the pyramid builders), we can take our time and push it slowly up the long ramp to the top of the shelf.

Understanding this allows us also to understand that simple machines involve what is called a "trade-off." The trade-off, or the something that is given up in order to get something else, is the increase in distance. So although we have to use less force to move a heavy object up a ramp, we have increased the distance we have to move it (because a ramp is not the shortest distance between two points). Most primitive people were happy to make this trade-off since it often meant being able to move something that they otherwise could not have moved.

Today, most machines are complicated and use several different elements like ball bearings or gears to do their work. However, when we look at them closely and understand their parts, we usually see that despite their complexity they are basically just two or more simple machines working together. These are called compound machines. Although some people say that there are less than six simple machines (since a wedge can be considered an inclined plane that is moving, or a pulley is a lever that rotates around a fixed point), most authorities agree that there are in fact six types of simple machines.

Lever

A lever is a stiff bar or rod that rests on a support called a fulcrum (pronounced FULL-krum) and which lifts or moves something. This may be one of the earliest simple machines, because any large, strong stick would have worked as a lever. Pick up a stick, wedge it under one edge of a rock, and push down and you have used a lever. Downward motion on one end results in upward motion on the other. Anything that pries something loose is also a lever, such as a crow bar or the claw end of a hammer. There are three types or classes of levers. A first-class lever has the fulcrum or pivot point located near the middle of the tool and what it is moving (called the resistance force). A pair of scissors and a seesaw are good examples. A second-class lever has the resistance force located between the fulcrum and the end of the lever where the effort force is being made. Typical examples of this are a wheelbarrow, nutcracker, and a bottle opener. A third-class lever has the effort force being applied between the fulcrum and the resistance force. Tweezers, ice tongs, and shovels are good examples. When you use a shovel, you hold one end steady to act as a fulcrum, and you use your other hand to pull up on a load of dirt. The second hand is the effort force, and the dirt being picked up is

the resistance force. The effort applied by your second hand lies between the resistance force (dirt) and the fulcrum (your first hand).

Pulley

A pulley consists of a grooved wheel that turns freely in a frame called a block through which a rope runs. In some ways, it is a variation of a wheel and axle, but instead of rotating an axle, the wheel rotates a rope or cord. In its simplest form, a pulley"s grooved wheel is attached to some immovable object, like a ceiling or a beam. When a person pulls down on one end of the rope, an object at the opposite end is raised. A simple pulley gains nothing in force, speed, or distance. Instead, it only changes the direction of the force, as with a Venetian blind (up or down). Pulley systems can be movable and very complex, using two or more connected pulleys. This permits a heavy load to be lifted with less force, although over a longer distance.

Wheel and axle

The wheel and axle is actually a variation of the lever (since the center of the axle acts as the fulcrum). It may have been used as early as 3000 b.c., and like the lever, it is a very important simple machine. However, unlike the lever that can be rotated to pry an object loose or push a load along, a wheel and axle can move a load much farther. Since it consists of a large wheel rigidly attached to a small wheel (the axle or the shaft), when one part turns the other also does. Some examples of the wheel and axle are a door knob, a water wheel , an egg beater, and the wheels on a wagon, car, or bicycle. When force is applied to the wheel (thereby turning the axle), force is increased and distance and speed are decreased. When it is applied to the axle (turning the wheel), force is decreased and distance and speed are increased.

Inclined plane

An inclined plane is simply a sloping surface. It is used to make it easier to move a weight from a lower to a higher spot. It takes much less effort to push a wheel barrow load slowly up a gently sloping ramp than it does to pick it up and lift it to a higher spot. The trade-off is that the load must be moved a greater distance. Everyday examples are stairs, escalators, ladders, and a ship"s plank.

Wedge

A wedge is an inclined plane that moves and is used to increase force— either to separate something or to hold things together. With a wedge, the object or material remains in place while the wedge moves. A wedge can have a single sloping surface (like a door stop that holds a door tightly in place), or it can have two sloping surfaces or sides (like the wedge that splits a log in two). An axe or knife blade is a wedge, as is a chisel, plow, and even a nail.

Screw

A screw can be considered yet another form of an inclined plane, since it can be thought of as one that is wrapped in a spiral around a cylinder or post. In everyday life, screws are used to hold things together and to lift other things. When it is turned, a screw converts rotary (circular) motion into a forward or backward motion. Every screw has two parts: a body or post around which the inclined plane is twisted, and the thread (the spiraled inclined plane itself). Every screw has a thread, and if you look very closely at it, you will see that the threads form a tiny "ramp"

that runs from the tip to the top. Like nails, screws are used to hold things together, while a drill bit is used to make holes. Other examples of screws are airplane and boat propellers.

In physics, a simple machine is any device that requires the application of only one force in order to perform work. Work is the product of the force applied and the distance moved due to the force. Most authorities list six kinds of simple machines: levers, pulleys, wheels and axles, inclined planes, wedges, and screws. One can argue, however, that these six machines are not entirely different from each other. Pulleys and wheels and axles, for example, are really special kinds of levers, and wedges and screws are special kinds of inclined planes.

Levers

A lever is a simple machine that consists of a rigid bar supported at one point, known as the fulcrum. A force called the effort force is applied at one point on the lever in order to move an object, known as the resistance force, located at some other point on the lever. A common example of the lever is the crow bar used to move a heavy object such as a rock. To use the crow bar, one end is placed under the bar, which is supported at some point (the fulcrum) close to the rock. A person then applies a force at the opposite end of the crow bar to lift the rock. A lever of the type described here is a first-class lever because the fulcrum is placed between the applied force (the effort force) and the object to be moved (the resistance force).

The effectiveness of the lever as a machine depends on two factors: the forces applied at each end and the distance of each force from the fulcrum. The farther a person stands from the fulcrum, the more his or her force on the lever is magnified. Suppose that the rock to be lifted is only one foot from the fulcrum and the person trying to lift the rock stands 2 yd (1.8 m) from the fulcrum. Then, the person’ s force is magnified by a factor of six. If he or she pushes down with a force of 30 lb (13.5 kg), the object that is lifted can be as heavy as 180 (6 x 30) lb (81 kg).

Two other types of levers exist. In one, called a second-class lever, the resistance force lies between the

effort force and the fulcrum. A nutcracker is an example of a second-class lever. The fulcrum in the nutcracker is at one end, where the two metal rods of the device are hinged together. The effort force is applied at the opposite ends of the rods, and the resistance force, the nut to be cracked open, lies in the middle.

In a third-class lever, the effort force lies between the resistance force and the fulcrum. Some kinds of garden tools are examples of third-class levers. When a person uses a shovel, for example, one holds the handle end steady to act as the fulcrum, while using the other hand to pull up on a load of dirt. The second hand is the effort force, and the dirt being picked up is the resistance force. The effort applied by the second hand lies between the resistance force (the dirt) and the fulcrum (the first hand).

Mechanical advantage

The term mechanical advantage is used to described how effectively a simple machine works. Mechanical advantage is defined as the resistance force moved divided by the effort force used. In the lever example above, for example, a person pushing with a force of 30 lb (13.5 kg) was able to move an object that weighed 180 lb (81 kg). So, the mechanical advantage of the lever in that example was 180 lb divided by 30 lb, or 6.

The mechanical advantage described here is really the theoretical mechanical advantage of a machine. In actual practice, the mechanical advantage is always less than what a person might calculate. The main reason for this difference is resistance. When a person does work with a machine, there is always some resistance to that work. For example, a mathematician can calculate the theoretical mechanical advantage of a screw (a kind of simple machine) that is being forced into a piece of wood by a screwdriver. The actual mechanical advantage is much less than what is calculated because friction must be overcome in driving the screw into the wood.

Sometimes the mechanical advantage of a machine is less than one. That is, a person has to put in more force than the machine can move. Class three levers are examples of such machines. A person exerts more force on a class three lever than the lever can move. The purpose of a class three lever, therefore, is not to magnify the amount of force that can be moved, but to magnify the distance the force is being moved.

As an example of this kind of lever, imagine a person who is fishing with a long fishing rod. The person will exert a much larger force to take a fish out of the water than the fish itself weighs. The advantage of the fishing pole, however, is that it moves the fish a large distance, from the water to the boat or the shore.

Pulleys

A pulley is a simple machine consisting of a grooved wheel through which a rope runs. The pulley can be thought of as a kind of lever if one thinks of the grooved wheel as the fulcrum of the lever. Then the effort force is the force applied on one end of the pulley rope, and the resistance force is the weight that is lifted at the opposite end of the pulley rope.

In the simplest form of a pulley, the grooved wheel is attached to some immovable object, such as a ceiling or beam. When a person pulls down on one end of the pulley rope, an object at the opposite end of the rope is raised. In a fixed pulley of this design, the mechanical advantage is one. That is, a person can lift a weight equal to the force applied. The advantage of the pulley is one of direction. An object can be made to move upward or downward with such a pulley. Venetian blinds are a simple example of the fixed pulley.

In a movable pulley, one end of the pulley rope is attached to a stationary object (such as a ceiling or beam), and the grooved wheel is free to move along the rope. When a person lifts on the free end of the rope, the grooved wheel and any attached weight slides upward on the rope. The mechanical advantage of this kind of pulley is two. That is, a person can lift twice as much weight as the force applied on the free end of the pulley rope.

More complex pulley systems can also be designed. For example, one grooved wheel can be attached to a stationary object, and a second movable pulley can be attached to the pulley rope. When a person pulls on the free end of the pulley rope, a weight attached to the movable pulley can be moved upward with a mechanical advantage of two. In general, in more complicated pulley systems, the mechanical advantage of the pulley is equal to the number of ropes that hold up the weight to be lifted. Combinations of fixed and movable pulleys are also known as a block and tackle . Some blocks and tackles have mechanical advantages high enough to allow a single person to lift weights as heavy as that of an automobile.

Wheel and axle

A second variation of the lever is the simple machine known as a wheel and axle . A wheel and axle consists of two circular pieces of different sizes attached to each other. The larger circular piece is the wheel in the system, and the smaller circular piece is the axle. One of the circular pieces can be considered as the effort arm of the lever and the second, the resistance arm. The place at which the two pieces is joined is the fulcrum of the system.

Some examples of the wheel and axle include a door knob, a screwdriver, an egg beater, a water wheel , the steering wheel of an automobile, and the crank used to raise a bucket of water from a well. When the wheel in a wheel and axle machine is turned, so is the axle, and vice versa. For example, when someone turn the handle of a screwdriver, the edge that fits into the screw head turns at the same time.

The mechanical advantage of a wheel and axle machine can be found by dividing the radius of the wheel by the radius of the axle. For example, suppose that the crank on a water well turns through a radius of 2 ft (61 cm) and the radius of the axle around which the rope is wrapped is 4 in (10 cm). Then, the mechanical advantage of this wheel and axle system is 2 ft divided by 4 in, or 6.

Inclined planes

KEY TERMS

A machine consisting of two or more simple machines.

The force applied to a machine.

A force caused by the movement of an object through liquid, gas, or against a second object that works to oppose the first object"s movement.

A mathematical measure of the amount by which a machine magnifies the force put into the machine.

The force exerted by a machine.

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A simple machine is a mechanical device that consists of a minimum of moving parts but yet can create an improvement of the output over the input. The improvement could be creating a mechanical advantage or simply changing the direction of the output. Mechanical advantage is the increase of force, distance or speed from the input value.

Around the 16th century, the classic list of simple machines was determined. The list consisted of the lever, wheel and axle, pulley, inclined plane, wedge, and screw.

These simple machines can be broken into three classifications: lever simple machines, rotating simple machines, and inclined plane simple machines.

Questions you may have include:

• What do lever simple machines do?
• What do rotating simple machines do?
• What do inclined plane simple machines do?

This lesson will answer those questions. Useful tool: Units Conversion

Lever simple machines

The lever simply consists of a rod or board that pivots on a fulcrum, creating a mechanical advantage or a change in direction.

The lever is a classic simple machine that achieves a mechanical advantage according to the ratio of the output or load arm of the lever divided by the input or effort arm.

The mechanical advantage of a lever can concern force, distance, or speed of the output.

The efficiency of the lever is very high, since the loss due to friction at the fulcrum is low.

Rotating simple machines

Rotating simple machines include rollers, wheel and axle, crank, and pulley.

Rollers

The wheel or roller by itself can make it easier to move objects by overcoming friction.

Wheel and axle

When an axle is added to a wheel, a torque on the axle increases the speed of the outer surface of the wheel. Likewise, turning the wheel from its outer edge increases the force applied from the axle.

Crank

A crank is like a wheel and axle. You can push on the handle of a crank, and it will create a twisting force or torque on the axle. This is a variation of the wheel and axle.

Pulley

A pulley is a wheel and axle, that uses a rope to lift objects. A major purpose of a pulley is to change the direction of the input force. You can pull down one a pulley rope, and the rope will lift the object upward.

Complex set of pulleys

A complex set up pulleys, such as a block-and-tackle configuration, can result in a mechanical advantage. The question is that if it is a complex set, is it still a simple machine? Probably not.

Inclined plane simple machines

Variations of an inclined plane include a ramp, wedge, and screw.

Ramp

The inclined plane or ramp makes raising a weight to a given height easier, according to the angle of the incline. Unfortunately, the resistive force of friction from sliding the object on the ramp can negate the mechanical advantage.

Variations of the inclined plane are the wedge and screw.

Wedge

Although a wedge is considered a simple machine, it is really a special application of an inclined plane.

Screw

The screw is really an inclined plane that is wrapped around a shaft. Turning the shaft around its central axis transforms rotational motion and torque into axial motion and force.

A screw can also act like a wedge, forcing itself into a softer material.

Summary

Simple machines usually exchange using a smaller force over a greater distance to move a heavy object over a short distance. The work required is the same, but the force required is less. The are also simple machines that help to reduce the resistance of friction or such.

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Engineering Connection

Why do engineers care about simple machines? How do such devices help engineers improve society? Simple machines are important and common in our world today in the form of everyday devices (crowbars, wheelbarrows, highway ramps, etc.) that individuals, and especially engineers, use on a daily basis. The same physical principles and mechanical advantages of simple machines used by ancient engineers to build pyramids are employed by today"s engineers to construct modern structures such as houses, bridges and skyscrapers. Simple machines give engineers added tools for solving everyday challenges.

Learning Objectives

After this lesson, students should be able to:

• Understand what a simple machine is and how it would help an engineer to build something.
• Identify six types of simple machines.
• Understand how the same physical principles used by engineers today to build skyscrapers were employed in ancient times by engineers to build pyramids.
• Generate and compare multiple possible solutions to creating a simple lever machine based on how well each met the constraints of the challenge.

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Slide Right on by Using an Inclined Plane

Students explore building a pyramid, learning about the simple machine called an inclined plane. They also learn about another simple machine, the screw, and how it is used as a lifting or fastening device.

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Refreshed with an understanding of the six simple machines; screw, wedge, pully, incline plane, wheel and axle, and lever, student groups receive materials and an allotted amount of time to act as mechanical engineers to design and create machines that can complete specified tasks.

Pyramid Building: How to Use a Wedge

Students learn how simple machines, including wedges, were used in building both ancient pyramids and present-day skyscrapers. In a hands-on activity, students test a variety of wedges on different materials (wax, soap, clay, foam).

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All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN) , a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g. , by state; within source by type; e.g. , science or mathematics; within type by subtype, then by grade, etc .

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Introduction/Motivation

How did the Egyptians build the Great Pyramids thousands of years ago (~2,500 BCE)? Could you build a pyramid using 9,000-kilogram (~10-ton or 20,000-lb) blocks of stone with your bare hands? That"s like trying to move a large elephant with your bare hands! How many people might it take to move a block that big? It would still be a challenge to build a pyramid today even with modern tools, such as jackhammers, cranes, trucks and bulldozers. But without these modern tools, how did Egyptian workers cut, shape, transport and place enormous stones? Well, one key to accomplishing this amazing and difficult task was the use of simple machines.

Simple machines are devices with no, or very few, moving parts that make work easier. Many of today"s complex tools are really just more complicated forms of the six simple machines. By using simple machines, ordinary people can split huge rocks, hoist large stones, and move blocks over great distances.

However, it took more than just simple machines to build the pyramids. It also took tremendous planning and a great design . Planning, designing, working as a team and using tools to create something, or to get a job done, is what engineering is all about. Engineers use their knowledge, creativity and problem-solving skills to accomplish some amazing feats to solve real-world challenges. People call on engineers to use their understanding of how things work to do seemingly impossible jobs and make everyday activities easier. It is surprising how many times engineers turn to simple machines to solve these problems.

Once we understand simple machines, you will recognize them in many common activities and everyday items. (Hand out .) These are the six simple machines: wedge, wheel and axle, lever, inclined plane, screw , and pulley . Now that you see the pictures, do you recognize some of these simple machines? Can you see any of these simple machines around the classroom? How do they work? Well, an important vocabulary term when learning about simple machines is mechanical advantage . Mechanical advantage of simple machines means we can use less force to move an object, but we have to move it a longer distance. A good example is pushing a heavy object up a ramp. It may be easier to push the object up a ramp instead of just lifting it up to the right height, but it takes a longer distance. A ramp is an example of the simple machine called an inclined plane . We are going to learn a lot more about each of these six simple machines that are a simple solution to helping engineers, and all humans, do hard work.

Sometimes it is difficult to recognize simple machines in our lives because they look different than the examples we see at school. To make our study of simple machines easier, let"s imagine that we are living in ancient Egypt and that the leader of the country has hired us as engineers to build a pyramid. Today"s availability of electricity and technologically-advanced machines make it difficult for us to see what the simple machine is accomplishing. But in the context of ancient Egypt, the simple machines that we will study are the much more basic tools of the time. After we develop an understanding of simple machines, we will shift our context to building a skyscraper in the present day, so we can compare and contrast how simple machines were used across the centuries and are still used today.

Lesson Background and Concepts for Teachers

Use the attached Introduction to Simple Machines PowerPoint presentation and Simple Machines Reference Sheet as helpful classroom tools. (Show the PowerPoint presentation, or print out the slides to use with an overhead projector. The presentation is animated to promote an inquiry-based style; each click reveals a new point about each machine; have students suggest characteristics and examples before you reveal them.)

Simple machines are everywhere; we use them everyday to perform simple tasks. Simple machines have also been in use since the early days of human existence. While simple machines take many shapes, they come in six basic types:

• Wedge : A device that forces things apart.
• Wheel and axle : Used to reduce friction.
• Lever : Moves around a pivot point to increase or decrease mechanical advantage.
• Inclined plane : Raises objects by moving up a slope.
• Screw : A device that can lift or hold things together.
• Pulley : Changes the direction of a force.

We use simple machines because they make work easier. The scientific definition of work is the amount of force that is applied to an object multiplied by the distance the object is moved. Thus, work consists of force and distance. Each job takes a specific amount of work to finish it, and this number does not change. Thus, the force times the distance always equals the same amount of work. This means that if you move something a smaller distance you need to exert a greater force. On the other hand, if you want to exert less force, you need to move it over a greater distance. This is the force and distance trade off, or mechanical advantage , which is common to all simple machines. With mechanical advantage, the longer a job takes, the less force you need to use throughout the job. Most of the time, we feel that a task is hard because it requires us to use a lot of force. Therefore, using the trade off between distance and force can make our task much easier to complete.

The wedge is a simple machine that forces objects or substances apart by applying force to a large surface area on the wedge, with that force magnified to a smaller area on the wedge to do the actual work. A nail is a common wedge with a wide nail head area where the force is applied, and a small point area where the concentrated force is exerted. The force is magnified at the point, enabling the nail to pierce wood. As the nail sinks into the wood, the wedge shape at the point of the nail moves forward, and forces the wood apart.

Figure 1: An axe is an example of a wedge.

Everyday examples of wedges include an axe (see Figure 1), nail, doorstop, chisel, saw, jackhammer, zipper, bulldozer, snow plow, horse plow, zipper, airplane wing, knife, fork and bow of a boat or ship.

The wheel and axle is a simple machine that reduces the friction involved in moving an object, making the object easier to transport. When an object is pushed, the force of friction must be overcome to start it moving. Once the object is moving, the force of friction opposes the force exerted on the object. The wheel and axle makes this easier by reducing the friction involved in moving an object. The wheel rotates around an axle (essentially a rod that goes through the wheel, letting the wheel turn), rolling over the surface and minimizing friction. Imagine trying to push a 9,000-kilogram (~10-ton) block of stone. Wouldn"t it be easier to roll it along using logs placed underneath the stone?

Everyday examples of the wheel and axle include a car, bicycle, office chair, wheel barrow, shopping cart, hand truck and roller skates.

A lever simple machine consists of a load, a fulcrum and effort (or force). The load is the object that is moved or lifted. The fulcrum is the pivot point, and the effort is the force required to lift or move the load. By exerting a force on one end of the lever (the applied force), a force at the other end of the lever is created. The applied force is either increased or decreased, depending on the distance from the fulcrum (the point or support on which a lever pivots) to the load, and from the fulcrum to the effort.

Figure 2: A crowbar is an example of a lever.

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Copyright © 2004 Microsoft Corporation, One Microsoft Way, Redmond, WA 98052-6399 USA. All rights reserved. With notations by the ITL Program, University of Colorado at Boulder, 2005.

Everyday examples of levers include a teeter-totter or see-saw, crane arm, crow bar, hammer (using the claw end), fishing pole and bottle opener. Think of a how you use a crowbar (see Figure 2). By pushing down on the long end of the crowbar, a force is created at the load end over a smaller distance, once again, demonstrating the tradeoff between force and distance.

Inclined planes make it easier to lift something. Think of a ramp. Engineers use ramps to easily move objects to a greater height. There are two ways to raise an object: by lifting it straight up, or by pushing it diagonally up. Lifting an object straight up moves it over the shortest distance, but you must exert a greater force. On the other hand, using an inclined plane requires a smaller force, but you must exert it over a longer distance.

Everyday examples of inclined planes include highway access ramps, sidewalk ramps, stairs, inclined conveyor belts, and switchback roads or trails.

Figure 3: A car jack is an example of a screw-type simple machine that enables one person to lift up the side of a car.

A screw is essentially an inclined plane wrapped around a shaft. Screws have two primary functions: they hold things together, or they lift objects. A screw is good for holding things together because of the threading around the shaft. The threads grip the surrounding material like teeth, resulting in a secure hold; the only way to remove a screw is to unwind it. A car jack is an example of a screw being used to lift something (see Figure 3).

Everyday examples of screws include a screw, bolt, clamp, jar lid, car jack, spinning stool and spiral staircase.

Figure 4: A pulley on a ship helps people pull in a heavy fishing net.

A pulley is a simple machine used to change the direction of a force. Think of raising a flag or lifting a heavy stone. To lift a stone up into its place on a pyramid, one would have to exert a force that pulls it up. By using a pulley made from a grooved wheel and rope, one can pull down on the rope, capitalizing on the force of gravity, to lift the stone up . Even more valuable, a system of several pulleys can be used together to reduce the force needed to lift an object.

Everyday examples of pulleys in use include flag poles, elevators, sails, fishing nets (see Figure 4), clothes lines, cranes, window shades and blinds, and rock climbing gear.

Compound Machines

A compound machine is a device that combines two or more simple machines. For example, a wheelbarrow combines the use of a wheel and axle with a lever. Using the six basic simple machines, all sorts of compound machines can be made. There are many simple and compound machines in your home and classroom. Some examples of the compound machines you may find are a can opener (wedge and lever), exercise machines/cranes/tow trucks (levers and pulleys), shovel (lever and wedge), car jack (lever and screw), wheel barrow (wheel and axle and lever) and bicycle (wheel and axle and pulley).

Vocabulary/Definitions

Design: (verb) To plan out in systematic, often graphic form. To create for a particular purpose or effect. Design a building. (noun) A well thought-out plan.

Engineering: Applying scientific and mathematical principles to practical ends such as the design, manufacture and operation of efficient and economical structures, machines, processes and systems.

Force: A push or pull on an object.

Inclined plane: A simple machine that raises an object to greater height. Usually a straight slanted surface and no moving parts, such as a ramp, sloping road or stairs.

Lever: A simple machine that increases or decreases the force to lift something. Usually a bar pivoted on a fixed point (fulcrum) to which force is applied to do work.

Mechanical advantage: An advantage gained by using simple machines to accomplish work with less effort. Making the task easier (which means it requires less force), but may require more time or room to work (more distance, rope, etc.). For example, applying a smaller force over a longer distance to achieve the same effect as applying a large force over a small distance. The ratio of the output force exerted by a machine to the input force applied to it.

Pulley: A simple machine that changes the direction of a force, often to lift a load. Usually consists of a grooved wheel in which a pulled rope or chain runs.

Pyramid: A massive structure of ancient Egypt and Mesoamerica used for a crypt or tomb. The typical shape is a square or rectangular base at the ground with sides (faces) in the form of four triangles that meet in a point at the top. Mesoamerican temples have stepped sides and a flat top surmounted by chambers.

Screw: A simple machine that lifts or holds materials together. Often a cylindrical rod incised with a spiral thread.

Simple machine: A machine with few or no moving parts that is used to make work easier (provides a mechanical advantage). For example, a wedge, wheel and axle, lever, inclined plane, screw, or pulley.

Spiral: A curve that winds around a fixed center point (or axis) at a continuously increasing or decreasing distance from that point.

Tool: A device used to do work.

Wedge: A simple machine that forces materials apart. Used for splitting, tightening, securing or levering. It is thick at one end and tapered to a thin edge at the other.

Wheel and axle: A simple machine that reduces the friction of moving by rolling. A wheel is a disk designed to turn around an axle passed through the center of the wheel. An axle is a supporting cylinder on which a wheel or a set of wheels revolves.

Work: Force on an object multiplied by the distance it moves. W = F x d (force multiplied by distance).

Associated Activities

• Stack It Up! - Students analyze and begin to design a pyramid. They perform calculations to determine the area of their pyramid base, stone block volumes, the number of blocks required for their pyramid base, and make a scaled drawing of a pyramid on graph paper.
• Choosing a Pyramid Site - Working in engineering project teams, students choose a site for the construction of a pyramid. They base their decision on site features as provided by a surveyor"s report; distance from the quarry, river and palace; and other factors they deem important to the project.

Lesson Closure

Today, we have discussed six simple machines. Who can name them for me? (Answer: Wedge, wheel and axle, lever, inclined plane, screw, and pulley.) How do simple machines make work easier? (Answer: Mechanical advantage enables us to use less force to move an object, but we have to move it a longer distance.) Why do engineers use simple machines? (Possible answers: Engineers creatively use their knowledge of science and math to make our lives better, often using simple machines. They invent tools that make work easier. They accomplish huge tasks that could not be done without the mechanical advantage of simple machines. They design structures and tools to use our environmental resources better and more efficiently.) Tonight, at home, think about everyday examples of the six simple machines. See how many you can find around your house!

Complete the KWL Assessment Chart (see the Assessment section). Gauge students" understanding of the lesson by assigning the Simple Machines Worksheet as a take-home quiz. As an extension, use the attached . Review the information and answer any questions. Suggest the students keep the sheet handy in their desks, folders or journals.

Lesson Summary Assessment

Closing Discussion: Conduct an informal class discussion, asking the students what they learned from the activities. Ask the students:

• Who can name the different types of simple machines? (Answer: Wedge, wheel and axle, lever, inclined plane, screw, and pulley.)
• How do simple machines make work easier? (Answer: Mechanical advantage enables us to use less force to move an object, but we have to move it a longer distance.)
• Why do engineers use simple machines? (Possible answers: Engineers creatively use their knowledge of science and math to make our lives better, often using simple machines. They invent tools that make work easier. They accomplish huge tasks that could not be done without the mechanical advantage of simple machines. They design structures and tools to use our environmental resources better and more efficiently.)

Remind students that engineers consider many factors when they plan, design and create something. Ask the students:

• What are the considerations an engineer must keep in mind when designing a new structure? (Possible answers: Size and shape (design) of the structure, available construction materials, calculation of materials needed, comparing materials and costs, making drawings, etc.)
• What are the considerations an engineer must keep in mind when choosing a site to build a new structure? (Possible answers: Site physical characteristics , distance to construction resources , suitability for the structure"s purpose .)

KWL Chart (Conclusion): As a class, finish column L of the KWL Chart as described in the Pre-Lesson Assessment section. List all of the things they learned about simple machines. Were all of the W questions answered? What new things did they learn?

Take-Home Quiz: Gauge students" understanding of the lesson by assigning the Simple Machines Worksheet as a take-home quiz.

Lesson Extension Activities

Use the attached Simple Machines Scavenger Hunt! Worksheet to conduct a fun scavenger hunt. Have the students find examples of all the simple machines used in the classroom and their homes.

Bring in everyday examples of simple machines and demonstrate how they work.

Illustrate the power of simple machines by asking students to do a task without using a simple machine, and then with one. For example, create a lever demonstration by hammering a nail into a piece of wood. Have students try to pull the nail out, first using only their hands

Bring in a variety of everyday examples of simple machines. Hand out one out to each student and have them think about what type of simple machine it is. Next, have students place the items into categories by simple machines and explain why they chose to place their item there. Ask students what life would be like without this item. Emphasize that simple machines make our life easier.

See the Edheads website for an interactive game on simple machines: http://edheads.org.

Engineering Design Fun with Levers: Give each pair of students a paint stirrer, 3 small plastic cups, a piece of duct tape and a wooden block or spool (or anything similar). Challenge the students to design a simple machine lever that will throw a ping pong ball (or any other type of small ball) as high as possible. In the re-design phase, allow the students to request materials to add on to their design. Have a small competition to see which group was able to send the ping pong ball flying high. Discuss with the class why that particular design was successful versus other variations seen during the competition.

Additional Multimedia Support

See http://edheads.org for a good simple machines website with curricular materials including educational games and activities.

References

Dictionary.com. Lexico Publishing Group, LLC. Accessed January 11, 2006. (Source of some vocabulary definitions, with some adaptation) http://www.dictionary.com

Simple Machines. inQuiry Almanack, The Franklin Institute Online, Unisys and Drexel eLearning. Accessed January 11, 2006. http://sln.fi.edu/qa97/spotlight3/spotlight3.html

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Acknowledgements

The contents of these digital library curricula were developed by the Integrated Teaching and Learning Program under National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government. 

Last modified: February 11, 2019