forces and machines - the time piece -...

140 Unit 1: Matter and Energy

Forces andMachines

Balls move through thissculpture. What do you thinkkeeps the balls in motion?

Prepare and practice for the FCAT

• Section Reviews, pp. 14, 25, 33, 38

• Chapter Review, pp. 34–36• FCAT Practice, p. 37

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Review and FCAT Practice

Machines help peopledo work by changingthe force applied to an object.

Key Concepts

Forces can causechange.Learn about how forces affectmotion and transfer energy.

Machines help people do work.Learn about machines andhow they are used to do work.

Six simple machineshave many uses.Learn about levers, inclinedplanes, and other simplemachines that are related to them.

Modern technologyuses compoundmachines.Learn how scientists use nanotechnology and robots.

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Chapter 5: Forces and Machines 141

Changing DirectionObserve how a window blind works. Notice how you use a downward force to pull the blind up. Look around you for other examples.

Observe and ThinkWhy does changing the direction of a force make some tasks easier?

Shut the Door!Find a door that swings freely on its hinges. Stand on the side where you can push the door to close it. Open the door. Push the door closed several times, placing your hand closer to or farther from the hinges each time.

Observe and Think Which hand placement made it easiest to shut the door? Why do you think that was so?

Internet Activity: MachinesGo to ClassZone.com to learn more about thesimple machines in everyday objects. Select anitem and think abouthow it moves and doesits job. Then test yourknowledge of simplemachines.

Observe and ThinkWhat other objects contain simple machines?

NSTA scilinks.org

Simple Machines Code: MDL008

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Content Review and FCAT Practice


TAKING NOTES

CHOOSE YOUR OWN STRATEGY

To take notes, use one ormore of the strategiesfrom earlier chapters—main idea web, main ideaand detail notes, and mindmap. Feel free to mix andmatch the strategies, oruse an entirely differentnote-taking strategy.

VOCABULARYSTRATEGY

Draw a word triangle dia-gram for each new vocab-ulary term. On the bottomline, write and define theterm. Above that, write asentence in which the termis used correctly. At the top,draw a small picture toillustrate the term.

CONCEPT REVIEW

• Matter is made of particlestoo small to see.

• Matter can be solid, liquid, or gas.

• Energy is the ability to cause a change.

• There are different forms of energy.

VOCABULARY REVIEW

matter p. 49

energy p. 112

kinetic energy p. 114

potential energy p. 115

CHAPTER 5

Main Idea Web

A force is a push or a pull.

When I push on a

box, I apply a force to it.


Content Review and FCAT Practice

DETAIL NOTESMAIN IDEAS

Main Idea and Detail Notes

Mind Map

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FCAT VOCABULARYforce p. 143speed p. 145

VOCABULARYmotion p. 144work p. 149

BEFORE, you learned• Energy causes change• Kinetic energy is the energy

of motion• Energy can be transferred or

changed in form, but nevercreated or destroyed

NOW, you will learn• How motion is measured• How forces affect motion• How force, energy, and work

are related

KEY CONCEPT

Forces can cause change.

EXPLORE Motion

How can motion be measured?

PROCEDURE

Practice tapping the marker on the scrap paper at regular intervals of two times per second.

Once you feel your tapping intervals are consis-tent, position your pen at one end of the long paper. Start tapping. Close your eyes and have a partner start pullingthe paper under the marker. Your partner should vary the speed ofthe paper at least twice but pull slowly enough that you have timeto make at least two dots at each speed.

Stop tapping when your partner tellsyou the marker is now at the otherend of the paper. Open your eyesand study the trail of dots.

WHAT DO YOU THINK?Which part of the dot trail showswhere the paper was being pulledthe fastest? How can you tell?

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Forces affect matter.What happens when you kick a soccer ball on a grassy field? When youkick a ball, you apply a force to it. A is a push or a pull. Forces canchange the way that matter moves. For example, if the ball is not moving,your kick may start the ball rolling across the field. Other forces maystop the ball or change its direction. In this section, you will learn aboutthe role that forces play in changing the motion of objects and intransferring energy from one object to another.

force

MATERIALS• felt-tip marker• scrap paper• 2 sheets of plain paper

taped end to end

Sunshine StateSTANDARDSSC.C.1.3.1: The studentknows that the motionof an object can bedescribed by its posi-tion, direction ofmotion, and speed.SC.C.2.3.3: The studentknows that if more thanone force acts on anobject, then the forcescan reinforce or canceleach other, dependingon their direction andmagnitude.SC.C.2.3.5: The studentunderstands that anobject in motion willcontinue at a constantspeed and in a straightline until acted upon bya force and that anobject at rest willremain at rest untilacted upon by a force.

NOTE-TAKING STRATEGYYou could take notes onforces by using a mainidea web.


Changes in motion can be measured.To understand how forces affect motion, first you must be able tomeasure motion and changes in motion. To describe how an object ismoving, you need to determine where it is and how fast it is moving.

Finding Positionis a change in position over time. The position of a place or

object is the location of that place or object. Position, however, can bedescribed only in relation to another location.

For example, suppose you tell a friend that your school is two blocksaway. Do you mean two blocks from where you are now or two blocksfrom your home or two blocks from your friend’s home?

To describe a position, you need to compare the location of theobject or place with another location, called a reference point. Forexample, you could compare the position of Tallahassee, Florida, withthat of Orlando, Florida, by saying that Tallahassee is 356 kilometers(221 mi) northwest of Orlando. Notice that you need both distanceand direction to describe the location completely. Most positions onEarth can be described by means of distances and directions from reference points.

Check Your Reading What information is needed to describe a position?

Motion

Position is measured from a reference point.

Using Distance and Direction

How would you describe the position of Orlando usingTallahassee as a reference point?

The way you woulddescribe the location ofTallahassee depends onyour reference point.Shown here are the dis-tance and direction ofTallahassee with Orlandoused as a reference point.

Gulf of Mexico

Orlando

Tallahassee

AT L A N T I CO C E A N

ALABAMA GEORGIA

FLORIDA

0 50 100 kilometers

0 50 100 milesN

S

EW

Reference Point: Orlando


Finding SpeedWhen you run a race, your position changes continuously as you run.How much your position changes each second is your speed. The of an object is a measure of how far the object moves in a given amountof time. The formula for average speed is shown below.

Average speed = �di

tsitman

ece

� v– = �dt�

In the formula, speed is shown by the letter v with a bar over it.The distance the object travels (d) is divided by the amount of time (t)that it takes the object to travel that distance. For example, the girl inthe diagram below travels 8 meters in 2 seconds. In standard units, dis-tance is measured in meters, and time is measured in seconds. Speed ismeasured in meters per second (m/s). The girl’s average speed is 8 mdivided by 2 s, or 4 m/s.

There are other common ways to measure distance and time, givingdifferent units for speed. For example, if a car travels 30 miles in anhour, you could say that its average speed is 30 miles per hour (mi/hor mph). A speed of 1 mile per hour is equal to a speed of about 1.6kilometers per hour, or 0.45 meter per second.

The speed of an object often changes with time. The object mightmove faster or slower at any given moment. It is hard to find the speedan object has at any specific moment, but you can still find the averagespeed over a given time interval by using the formula. Suppose that thegirl in the diagram above continued to ride her bicycle for several hours.Over those hours, she might go faster as she biked down a hill, slowdown as she got tired, or even stop to rest. Although the girl’s speedmay change as she rides, you can still find her average speed for thewhole trip. The girl’s average speed is equal to the total distance sherode divided by the total time it took her to travel that distance.

Check Your Reading What measurements should you make if you want to determinethe speed of an object?

speed

2 3

00:00

1

00:0200:01

4 8 Distancein meters

Time inseconds

reminder

The bar over the letter v inthe formula means “aver-age.” It is the average speedthat is being calculated.


Does walking speed dependon leg length?Some people think that having long legs enables aperson to walk faster. Compare your average speedand your leg length with those of others to see if there is a relationship.

PROCEDURE

Develop and carry out a procedure for measuring the distance from your hipto the floor. Record this distance as your leg length.

Decide upon a procedure for determining your average walking speed, usingthe materials provided. Remember that you will need to make more than oneset of measurements when you design your procedure.

Following your procedure, perform at least five trials. Try not to change yourspeed, but walk the way you normally would. Record your data and use thedata to calculate your speed in meters per second for each trial.

Calculate the average of your speed measurements. Collect data on leglengths and average speeds from other students in the class. Plot all the dataas points on a graph, with leg length on the x-axis and average speed onthe y-axis.

WHAT DO YOU THINK?From your graph, what conclusions can youdraw about speed and leg length?

CHALLENGE If your teacher has data for otherclasses, add them to your graph. Does this newinformation change your conclusions?

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SpeedSpeedSKILL FOCUSDesigning experiments

MATERIALS• masking tape• meter stick• stopwatch• string• calculator• graph paper

TIME30 minutes

Forces can change motion.When you let go of a book you are holding, why does it fall? The forceof Earth’s gravity pulls the book downward. Gravity is a force that actsto pull everything on Earth toward Earth’s center. If there were nogravity, the book would stay where you let go of it unless some otherforce were acting on it. The motion of an object does not changeunless a force acts on the object.

Changing MotionA ball does not start moving all by itself. To move a ball, you have tokick it, throw it, or apply a force to it in some other way. An object thatis not moving will not start moving unless a force is applied to it.


In fact, even moving objects do not change their motion unlessforces act on them. A moving object with no forces acting on it con-tinues to move at the same speed and in the same direction. A boxsliding across a floor would never slow down if no forces were actingon it. Then why does a sliding box slow down and stop? When anobject slides over a surface, friction acts against the motion. Friction isa force that causes the box to slow down until it finally stops.

A force can change the motion of an object by changing the object’sspeed or the direction the object is moving or both. For example, a ballresting in a volleyball player’s hand will not move unless a force acts onit, as shown in the upper picture below. When the player hits the ball,the force of her hit will cause the ball to move. A volleyball player canalso change the speed or direction of a moving ball by applying a forceto it, as shown in the picture on the bottom.

Objects at rest remain at rest, and objects in motion remain in thesame motion, unless the objects are acted on by forces.

Forces Change Motion

An Object at Rest

What will happen to the ball’s motion in each picture? Why?

object at rest

force

force (from the fist)

object at rest (ball)

object in motion

force

object in motion(ball)

force (from the arms)

object in motion

An object at rest (the ball) remains atrest unless a force(from the fist) acts on it.

An object in motion (the ball) remains in thesame motion unless aforce (from the arms)changes the motion.

An Object in Motion


Multiple ForcesSometimes when you push on a heavy piece of furniture, such as adesk, it doesn’t move. The force of friction on the desk acts againstyour push. To move the desk, you have to apply a force greater thanthe force of friction. An object can have more than one force acting on it at the same time. How multiple forces change the motion of anobject depends upon the way in which the forces combine.

When a team plays tug-of-war, each player on the team pulls onthe rope in the same direction. The many individual forces have thesame effect on the rope as a single larger force would. Forces that actin the same direction add together to make a larger force.

Forces that act in opposite directions, however, tend to cancel eachother out. Consider what happens when two teams pull on oppositesides of a rope, as in the pictures below. In each case, the total forceacting on the rope is the difference between the two forces applied bythe teams. If both sides pull with the same force, as shown in the topphoto, the forces are balanced. The motion of the rope does notchange—the rope does not move. If one side pulls harder than theother, as shown in the bottom photo, the forces are unbalanced, andthe rope moves toward the stronger team.

balanced forces

unbalanced forces

If both teams pull with equal forcesin opposite directions, the two forcescancel each other. The rope stays atrest, as if no force were acting on it.

If one team pulls with more forcethan the other team, the forces do notcancel each other. The total force onthe rope is the difference betweenthe greater force in one direction andthe smaller force in the other direc-tion. The total force on the rope isunbalanced, and the rope moves.

SIMULATIONCLASSZONE.COM

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Forces can transfer energy.One way forces can transfer energy is in the form of waves. If you dropa pebble into a bowl of water, the pebble applies a force that disturbsthe water. The disturbance—which can be seen as ripples, or tiny waves,in the water—carries energy outward from the force to the edges ofthe bowl. These waves transfer energy through the water to the sidesof the bowl.

Forces can also transfer energy from one object directly to another.Consider what happens when you throw a ball. Your force on the ballcauses it to move faster. In other words, the force from your handincreases the ball’s kinetic energy. You have done work on the ball.

Forces and WorkIn physical science, the word work has a very specificmeaning. is the use of force to move an objectover some distance. Work is done only by the part ofthe force that is in the same direction as the motion.If you lift a box, you do work on it. If you walk withthe box, the small forward force that you apply tomove the box forward is doing work. Holding thebox is not doing work, even if the box is heavy andyou are tired. The only time you do work is whenyou move the box.

When you lift the box, you also transfer energy—by lifting it, you give the box potential energy.The amount of energy you transfer to an object isequal to the amount of work that you do on theobject. Both work and energy are measured in unitscalled joules (J).

The work done by a force depends on the size ofthe force and the distance over which the force actson an object. A small force acting over a long distance,as when you push a box across the floor, can do as much work as a large force acting over a short distance, as when a bat hits a ball.The total work done by a force is given by the following formula:

Work = Force p distanceW = Fd

Force, F, is measured in newtons, and distance, d, is measured inmeters. Work, W, is measured in joules. So if you push a box a distanceof 5 meters, using a force of 20 newtons, the work you do is equal to 5 m p 20 N, or 100 J.

Work

This woman did workwhen she applied anupward force to lift the torch.

reminder

You have seen that weightis measured in newtons (N).This is because weight is aforce—the force of gravityon an object.

distance

force

Content Review

Waves can carry mechanicalenergy. For more about waveproperties, see page 749.

Content PreviewFLORIDA


Gaining and Losing EnergyAlthough one force can transfer energy to an object, other forces, suchas friction, may at the same time transfer energy away from that object.When you push a box across the floor at a constant speed, you transferenergy to the box, but the box does not gain kinetic energy. The resistingforce of friction balances your push. Friction between the box and thefloor heats the box and the floor. Although you are putting energy intothe box by doing work, the box is losing that energy as heat.

When the box loses as much energy to heat as you put into it,there is no overall change in the kinetic energy of the box. You are still doing work on the box, however, because you are using a force tomove the box. Your work does not increase the kinetic energy of thebox. Instead, your work on the box indirectly ends up increasing theenergy in the molecules of the box and the floor.

Although the man doeswork pushing the carts,most of the energy hetransfers to the carts islost to friction.

KEY CONCEPTS1. What changes when an object

moves?

2. If no forces are acting on amoving object, what happensto the object’s motion?

3. Describe two ways in whichenergy can be transferred.

CRITICAL THINKING4. Calculate Juan walks 10 km

in 2 hours. What is his speed?

5. Analyze You push a box witha force of 5 N for 1 m andthen stop. The box slides foranother 4 m before stopping.How much work did you doon the box?

CHALLENGE6. Analyze Suppose you are

moving a small wagon bypulling on its handle. How willchanging the angle at whichyou pull the handle affect theamount of work you do on thewagon? Hint: Think aboutwhat happens if the handle isflat or is straight upward.


Sunshine StateSTANDARDSSC.B.1.3.4: The studentknows that energy con-versions are never 100%efficient (e.g., someenergy is transformedto heat and is unavail-able for further usefulwork).SC.C.2.3.4: The studentknows that simplemachines can be used tochange the direction orsize of a force.

BEFORE, you learned• Forces can change the motion

of objects• Work is done when a force is

exerted over a distance• Forces can transfer energy

NOW, you will learn• How machines help you

do work• How to calculate a machine‘s

efficiency

KEY CONCEPT

Machines help people do work.

EXPLORE Machines

How do machines help you work?

PROCEDURE

Look at one of the machines closely. Carefully operate the machine and notice how each part moves.

Sketch a diagram of the machine. Try to show all of the working parts. Add arrows and labels to show the direction of motion for each part.

WHAT DO YOU THINK?• What is the function of the machine?• How many moving parts does it have?• How do the parts work together?• How does this machine make work easier?

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MATERIALSvarious smallmachines

Machines change the way force is applied.For thousands of years, humans have been improving their lives with technology. Technology is the use of knowledge to create productsor tools that make life easier. The simplest machine is an example of technology.

A is any device that helps people do work. A machinedoes not decrease the amount of work that is done. Instead, a machinechanges the way in which work is done. Recall that work is the use offorce to move an object. If, for example, you have to lift a heavy box,you can use a ramp to make the work easier. Moving the box up aramp—which is a machine—helps you do the work by reducing theforce you need to lift the box.

machineVOCABULARYMake a word trianglediagram in your notebookfor machine.

FCAT VOCABULARYefficiency p. 156

VOCABULARYmachine p. 151mechanical advantage p. 153


A rake is a machine thatchanges a large force over a short distance to a smaller force over alarger distance.

If machines do not reduce the amount of work required, how dothey help people do work? Machines make work easier by changing

• the size of the force needed to do the work and the distance over which the force is applied

• the direction in which the force is exerted

Machines can be powered by different types of energy.Electronic machines, such as computers, use electrical energy.Mechanical machines, such as a rake, use mechanical energy.Often this mechanical energy is supplied by the person who is using the machine.

Changing Size and DistanceSome machines help you do work by changing the size of the forceneeded. Have you ever tried to open a door by turning the doorknob’sshaft instead of the handle? This is not easy to do. It takes less force toturn the handle of the doorknob than it does to turn the shaft.Turning the handle makes opening the door easier, even though youmust turn it through a greater distance.

If a machine—such as a doorknob attached to a shaft—allows you to exert less force, you must apply thatforce over a greater distance. The total amount of workremains the same whether it is done with a machine or not.You can think of this in terms of the formula for calculatingwork—work is force times distance. Because a machine doesnot decrease the amount of work to be done, less force mustmean greater distance.

A doorknob allows you to apply a smaller force over agreater distance. Some machines allow you to apply a greaterinput force over a shorter distance. Look at the boy using arake, which is a machine. The boy moves his hands a shortdistance to move the end of the rake a large distance, allowinghim to rake up more leaves.

Input force is the force exerted on a machine. Output forceis the force that a machine exerts on an object. The boy in thephotograph is exerting an input force on the rake. As a result,the rake exerts an output force on the leaves. The work theboy puts into the rake is the same as the work he gets out ofthe rake. However, the force he applies is greater than the force

the rake can apply to the leaves. The output force is less than the inputforce, but it acts over a longer distance.

Check Your Reading How can a rake help you do work? Use the word force in your answer.

input force

output force


Changing DirectionMachines also can help you work by changing thedirection of a force. Think of raising a flag on a flag-pole. You pull down on the rope, and the flag movesup. The rope system is a machine that changes thedirection in which you exert your force. The rope system does not change the size of the force, however.The force pulling the flag upward is equal to yourdownward pull.

A shovel is a machine that can help you dig a hole.Once you have the shovel in the ground, you pushdown on the handle to lift the dirt up. You can usesome of the weight of your body as part of your inputforce. That would not be possible if you were lifting the dirt by using only your hands. A shovel alsochanges the size of the force you apply, so you need lessforce to lift the dirt.

Mechanical Advantage of a MachineWhen machines help you work, there is an advantage—or benefit—to using them. The number of times a machine multipliesthe input force is called the machine’s (MA).To find a machine’s mechanical advantage, divide the output force bythe input force.

Mechanical Advantage =�OInu

ptp

uuttFFoorrccee

�

For machines that allow you to apply less force over a greater distance—such as a doorknob—the output force is greater than theinput force. Therefore, the mechanical advantage of this type ofmachine is greater than 1. For example, if the input force is 10 newtonsand the output force is 40 newtons, the mechanical advantage is 40 Ndivided by 10 N, or 4.

For machines that allow you to apply greater force over a shorterdistance—such as a rake—the output force is less than the input force.In this case, the mechanical advantage is less than 1. If the input forceis 10 newtons and the output force is 5 newtons, the mechanicaladvantage is 0.5. However, such a machine allows you to move anobject a greater distance.

Sometimes changing the direction of the force is more useful thandecreasing the force or the distance. For machines that change only thedirection of a force—such as the rope system on a flagpole—the inputforce and output force are the same. Therefore, the mechanical advantage of the machine is 1.

mechanical advantageAPPLY How does the ropesystem help the man raisethe flag?


Work transfers energy.Machines transfer energy to objects on which they do work. Every timeyou open a door, the doorknob is transferring mechanical energy tothe shaft. A machine that lifts an object gives it potential energy.A machine that causes an object to start moving, such as a baseball bat hitting a ball, gives the object kinetic energy.

EnergyWhen you lift an object, you transfer energy to it in the form ofgravitational potential energy—that is, potential energy caused bygravity. The higher you lift the object, the more work you must do, andthe more energy you give to the object. This is also true if a machinelifts an object. The gravitational potential energy of an object dependson its height above Earth’s surface, and it equals the work required tolift the object to that height.

In the diagram on page 155, the climber wants to reach the top ofthe hill. In order to reach the top, she must find some way to increase herpotential energy. The higher she climbs, the greater her potential energy.The added energy comes from the work the climber does. The potentialenergy she gains equals the amount of work she does.

WorkAs you have seen, when you use a machine to do work, there is alwaysan exchange, or tradeoff, between the force you use to do the workand the distance over which you apply that force. You apply less forceover a longer distance or greater force over a shorter distance.

To reach the top of the hill, the climber must do work. Because sheneeds to increase her potential energy by a certain amount, she mustdo the same amount of work to reach the top of the hill whether sheclimbs a steep slope or a gentle slope.

The sloping surface of the hill acts like a ramp, which is a simplemachine called an inclined plane. You know that machines make workeasier by changing the size or direction of a force. How does thismachine make the climber’s work easier?

As the climber goes up the hill, she is doing work against gravity.

One side of the hill is a very steep slope—almost straight up. If theclimber takes the steep slope, she climbs a shorter distance, but shemust use more force.

Another side of the hill is a long, gentle slope. Here the climbertravels a greater distance but uses much less effort.

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NOTE-TAKING STRATEGYRemember to organize yournotes in a chart or web asyou read.


If the climber uses the steep slope, she must lift almost her entire weight. The inclined plane allows her to exert her input force over alonger distance; therefore, she can use just enough force to overcomethe force pulling her down the inclined plane. This force is less thanher weight. In many cases, it is easier for people to use less force over alonger distance than it is for them to use more force over a shorterdistance.

To reach the top of the hill, the climber must do at least as muchwork as the amount of potential energy she needs to gain.

Energy and Work

By climbing the gentle slope,the climber covers more dis-tance but uses less force. Thework does not decrease eventhough the force does.

By climbing straight up the steep slope, the climbercovers a shorter distance but must apply more forceagainst gravity.

force

force

distance

dis

tan

ce

What combination of forces makes it more difficult to climb a steep slope? How might climbers try to overcome this problem?

The Short Route1

The Long Route2


Output work is always less than input work.The work you do on a machine is called the input work, and the workthe machine does in turn is called the output work. A machine’s

is the ratio of its output work to the input work. An idealmachine would be 100 percent efficient. All of the input work wouldbe converted to output work. Actual machines lose some input workto friction.

You can calculate the efficiency of a machine by dividing themachine’s output work by its input work and multiplying that number by 100.

Percent Efficiency = �WW

oorrkk

oiun

t� • 100 %e = �

W

Wo

i

u

n

t� • 100

Recall that work is measured in joules. Suppose you do 600 J of workin using a rope system to lift a box. The work done on the box is 540 J.You would calculate the efficiency of the rope system as follows:

Efficiency = �56

40

00

JJ

� p 100 = 90%

check your reading What is a machine’s efficiency? How does it affect the amount ofwork a machine can do?

efficiencyVOCABULARYWrite your own definitionof efficiency in a word triangle.

APPLY The mail carrier is riding a motorizedhuman transport machine.Suppose the machine hasan efficiency of 70 per-cent. How much work islost in overcoming frictionon the sidewalk and inthe motor?

Output work

Work lost

Input work

EfficiencyThe work you put into amachine will always begreater than the work doneby the machine. Some inputwork is always lost in over-coming friction.

Efficiency and EnergyYou know that work transfers energy and that machines make workeasier. The more mechanical energy is lost in the transfer to other formsof energy, the less efficient the machine. Machines lose some energy inthe form of heat due to friction. The more moving parts a machinehas, the more energy it loses to friction because the parts rub together.Machines can lose energy to other processes as well.

For example, a car engine has an efficiency of only about 25 percent.It loses much of the energy supplied by its fuel to heat from combustion.By comparison, a typical electric motor has more than an 80 percentefficiency. That means the motor converts more than 80 percent of theinput energy into mechanical energy, or motion.

Many appliances come with energy guides that can help a buyercompare the energy efficiency of different models. A washing machinewith the highest energy rating may not always save the most energy,however, because users may have to run those machines more often.

What is the efficiency of a ramp?PROCEDURE

Build a ramp as shown. Measure the vertical height of the ramp and the length of the ramp in centimeters. Convert these distances to meters and record.

Attach the block to the spring scale and measure the force in newtons needed to lift the block straight up. Record this force as the output force.Multiply the output force by the height of the ramp in meters to get the output work. Record the output work.

Use the spring scale to pull the block up the ramp with a constant force.Record the force measured on the spring scale as the input force. Multiply theinput force by the length of the ramp in meters to get the input work.Record the input work.

Use the input work and output work from steps 2 and 3 to calculate the efficiency of the ramp. Record your results.

WHAT DO YOU THINK?• How did your input work compare with your output work?

• What could you do to increase the efficiency of the ramp?

CHALLENGE Would adding sandpaper on the surface of the ramp increase or decrease the efficiency of the ramp? Why? Test your hypothesis.

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EfficiencyEfficiencySKILL FOCUSAnalyzing data

MATERIALS• board• books• meter stick• wooden block

with eye hook• spring scalefor Challenge:• sandpaper

TIME20 minutes



Increasing EfficiencyBecause all machines lose input work to friction, one way to improvethe efficiency of a machine is by reducing friction. Oil is used toreduce friction between the moving parts of car engines. The use ofoil makes engines more efficient.

Another machine that loses input work is a bicycle. Bicycles loseenergy to friction and to air resistance. Friction losses result from themeeting of the gears, from the action of the chain on the sprocket,and from the tires changing shape against the pavement. A bicycle withpoorly greased parts or other signs of poor maintenance requires moreforce to move. For a mountain bike that has had little maintenance,as much as 15 percent of the total work may be lost to friction.A well-maintained Olympic track bike, on the other hand, might lose only 0.5 percent.

check your reading What is a common way to increase a machine’s efficiency?

Proper maintenance can help keep a bicyclerunning as efficiently as possible.

KEY CONCEPTS1. In what ways can a machine

change a force?

2. How is a machine’s efficiencycalculated?

3. Why is a machine’s actualoutput work always less thanits input work?

CRITICAL THINKING4. Apply How would the input

force needed to push awheelchair up a ramp changeif you increased the height ofthe ramp but not its length?

5. Compare What is the difference between mechanicaladvantage and efficiency?

CHALLENGE6. Apply Draw and label a

diagram to show how to pulldown on a rope to raise a loadof construction materials.


How Efficient Are Machines?A hammer is used to pound in nails. It can also be used to pry nailsout of wood. When used to pry nails, a hammer is a machine calleda lever. Like all machines, the hammer is not 100 percent efficient.

Efficiency is the amount of work a machine does divided by the amount of work that is done on the machine. To calculate efficiency, you must first find the ratio of the machine’s outputwork to the input work done on the machine. A ratio is the com-parison of two numbers by means of division. You convert the ratioto a decimal by dividing. Then convert the decimal to a percent.

Answer the following questions.

1. A construction worker does 1000 J of work in pulling down ona rope to lift a weight tied to the other end. If the output workof the rope system is 550 J, what is the ratio of output work toinput work? What is the efficiency of the rope system?

2. If a machine takes in 20,000 J and puts out 5000 J, what is its efficiency?

3. You do 6000 J of work to pull a sled up a ramp. After you reachthe top, you discover that the sled had 3600 J of work done onit. What is the efficiency of the ramp?

CHALLENGE If you put 7000 J of work into a machine withan efficiency of 50 percent, how much work will you get out?

MATH TUTORIALCLASSZONE.COM

Click on Math Tutorial for more help with percents and fractions.

SKILL: CHANGING RATIOS TO PERCENTS

Example

A person is doing 1000 joules of work on a hammer to pry up a nail. The hammer does 925 joules of work on the nail to pull it out of the wood.

(1) Find the ratio of output work to input work.

�WW

oorkrk

oinut

� = = 0.925

(2) To convert the decimal to a percent, multiply 0.925 by 100and add a percent sign.

0.925 p 100 = 92.5%

ANSWER The efficiency of the hammer is 92.5 percent. This means that the hammer loses 7.5 percent of the input work to friction and other products.

925 J�1000 J

No machine, no matter how largeor small, is 100 percent efficient.Some of the input energy is lost tosound, heat, or other products.

http://www.classzone.com/redirect_science/fl_gr6_pg159_ratios.html

Sunshine StateSTANDARDSSC.C.2.3.4: The studentknows that simplemachines can be used tochange the direction orsize of a force.


BEFORE, you learned• Machines help you work by

changing the size or directionof a force

• The number of times amachine multiplies the input force is the machine’smechanical advantage

NOW, you will learn• How six simple machines

change the size or direction of a force

• How to calculate mechanicaladvantage

KEY CONCEPT

Six simple machineshave many uses.

EXPLORE Changing Forces

How can you change a force?

PROCEDURE

Lay one pencil on a flat surface. Place the other pencil on top of the first pencil and perpendicular to it, as shown. Place the book on one end of the top pencil.

Push down on the free end of the top pencil to raise the book.

Change the position of the bottom pencil so that it is closer to the book and repeat step 2. Then move the bottom pencil closer to the end of the pencil you are pushing on and repeat step 2.

WHAT DO YOU THINK?• How did changing the position of

the bottom pencil affect how much force you needed to lift the book?

• At which position is it easiest to lift the book? most difficult?

3

2

1

MATERIALS• 2 pencils• small book

There are six simple machines.You have read about how a ramp and a shovel can help you do work. A ramp is a type of inclined plane, and a shovel is a type of lever. An inclined plane and a lever are both simple machines.

are the six machines on which all other mechanicalmachines are based. In addition to the inclined plane and the lever,simple machines include the wheel and axle, pulley, wedge, and screw.As you will see, the wheel and axle and pulley are related to the lever,and the wedge and screw are related to the inclined plane. You willread about each of the six simple machines in detail in this section.

Simple machines

NOTE-TAKING STRATEGYAs you read, remember totake notes about the mainideas and supporting details.

FCAT VOCABULARYlever p. 161fulcrum p. 161wheel and axle p. 162pulley p. 162inclined plane p. 164wedge p. 164screw p. 165

VOCABULARYsimple machine p. 160

reading tip

The lengths of the arrows in the diagram representthe size of the force.


LeverA is a solid bar that rotates, or turns, around a fixed point. Thebar can be straight or curved. The fixed point is called the A lever can multiply the input force. It can also change the directionof the input force. If you apply a force downward on one end of alever, the other end can lift a load.

The way in which a lever changes an input force depends on thepositions of the fulcrum, the input force, and the output force in relationto one another. Levers with different arrangements have different uses.Sometimes a greater output force is needed, such as when you want to pry up a bottle cap. At other times you use a greater input force on one end to get a higher speed at the other end, such as when youswing a baseball bat. The three different arrangements, sometimescalled the three classes of levers, are shown in the diagram below.

check your reading What two parts are needed to make a lever?

fulcrum.

lever

Levers can be classified according to where the fulcrum is.

Levers

First-Class Lever

The fulcrum is locatedbetween the input force andthe output force. Use thistype of lever to change thedirection and size of a force.

fulcrum

inputforce

outputforce

Second-Class Lever

The output force is locatedbetween the input forceand the fulcrum. Use thistype of lever if you need agreater output force.

fulcrum

inputforce

outputforce

Third-Class Lever

fulcrum

inputforce output

force

The input force is locatedbetween the output force andthe fulcrum. Use this type oflever to reduce the distanceover which you apply theinput force or increase thespeed of the end of the lever.

Wheel and AxleA is a simple machine made of a wheel attached to ashaft, or axle. The wheels of most means of transportation—such as abicycle and a car—are attached to an axle. The wheel and axle act likea rotating collection of levers. The axle at the wheel’s center is like afulcrum. Other examples of wheels and axles are screwdrivers, steeringwheels, doorknobs, and electric fans.

Depending on your purpose for using a wheel and axle, you mightapply a force to turn the wheel or the axle. If you turn the wheel, yourinput force is transferred to the axle. Because the axle is smaller thanthe wheel, the output force acts over a shorter distance than the inputforce. A driver applies less force to a steering wheel to get a greaterturning force from the axle, or steering column. This makes it easier to steer the car.

If, instead, you turn the axle, your force is transferred to the wheel.Because the wheel is larger than the axle, the force acts over a longerdistance. A car also contains this use of a wheel and axle. The engineturns the drive axles, which turn the wheels.

check your reading Compare the results of putting force on the axle with puttingforce on the wheel.

PulleyA is a wheel with a grooved rim and a rope orcable that rides in the groove. As you pull on the rope,the wheel turns.

A pulley that is attached to something that holds itsteady is called a fixed pulley. An object attached to therope on one side of the wheel rises as you pull down onthe rope on the other side of the wheel. The fixed pulleymakes work easier by changing the direction of the force.You must apply enough force to overcome the weight ofthe load and any friction in the pulley system.

A fixed pulley allows you totake advantage of the downwardpull of your weight to move aload upward. It does not, how-ever, reduce the force you needto lift the load. Also, the distanceyou pull the rope through is thesame distance that the object islifted. To lift a load two metersusing a fixed pulley, you mustpull down two meters of rope.

pulley

wheel and axle

Fixed Pulley

162

Wheel and Axle

In a movable pulley setup, one end of the rope is fixed, but thewheel can move. The load is attached to the wheel. The person pullingthe rope provides the output force that lifts the load. A single movablepulley does not change the direction of the force. Instead, it multipliesthe force. Because the load is supported by two sections of rope, youneed only half the force you would use with a fixed pulley to lift it.However, you must pull the rope through twice the distance.

check your reading How does a single fixed pulley differ from a single movable pulley?

A combination of fixed and movable pulleys is a pulley systemcalled a block and tackle. A block and tackle is used to haul and liftvery heavy objects. By combining fixed and movable pulleys, you canuse more rope sections to support the weight of an object. This reducesthe force you need to lift the object. The mechanical advantage of asingle pulley can never be greater than 2. If engineers need a pulleysystem with a mechanical advantage greater than 2, they often use ablock-and-tackle system.

What is the mechanical advantage of a pulley system?PROCEDURE

Hang the mass on the spring scale to find its weight in newtons. Record thisweight as your output force.

Tie the top of one pulley to the ring stand.

Attach the mass to the second pulley.

Attach one end of the second pulley’s rope to the bottom of the first pulley. Then thread the free end of the rope through the second pulley. Loop the rope up and over the first pulley, as shown.

Attach the spring scale to the free end of the rope. Pull down to lift the mass. Record the force you used as your input force. Calculate the mechanical advantage of this pulley system. Hint: The mechanical advantage can be calculated by dividing the output force by the input force.

WHAT DO YOU THINK?• How did your input force compare with your output force?

• What caused the results you observed?

CHALLENGE Explain what the mechanical advantage would be for a pulley system that includes another movable pulley.

5

4

3

2

1

PulleysPulleysSKILL FOCUSInferring

MATERIALS• 100 g mass• spring scale• 2 pulleys with

rope• ring stand

TIME20 minutes

Movable Pulley


Inclined PlaneRecall that it is difficult to lift a heavy object straightup because you must apply a force great enough toovercome the downward pull of the force of gravity.For this reason people often use ramps. A ramp is an

a simple machine that is a slopingsurface. The photograph at the left shows the interiorof the Guggenheim Museum in New York City.The levels of the art museum are actually one continuous inclined plane.

Inclined planes make the work of raising an object easier becausethey support part of the weight of the object while it is being movedfrom one level to another. The surface of an inclined plane applies areaction force on the object resting on it. This extra force on theobject helps to act against gravity. If you are pushing an object up a ramp, you have to push with only enough force to overcome thesmaller net force that pulls the object down parallel to the incline.

The less steep an inclined plane is, the less force you need to push or pull an object on the plane. This is because a less steep planesupports more of an object’s weight than a steeper plane. However,the less steep an inclined plane is, the farther you must go to reach acertain height. While you use less force, you must apply that force over a greater distance.

check your reading How do inclined planes help people do work? Your answer should mention force.

WedgeA is a simple machine that has a thick endand a thin end. Wedges are used to cut, split, orpierce objects—or to hold objects together. A wedgeis a type of inclined plane, but inclined planes arestationary, while wedges often move to do work.

Some wedges are single, movable inclined planes,such as a doorstop, a chisel, or an ice scraper.Another kind of wedge is made of two back-to-backinclined planes. Examples include the blade of an axeor a knife. In the photograph at the left, a sculptor is using a chisel to shape stone. The sculptor appliesan input force on the chisel by tapping its thickerend with a mallet. That force pushes the thinner end of the chisel into the stone. As a result, the sides of the thinner end exert an output force thatseparates the stone.

wedge

inclined plane,

Inclined Plane


Wedge


The angle of the cutting edge determines how easily a wedge cancut through an object. Thin wedges have small angles and need lessinput force to cut than do thick wedges with large angles. That is whya sharp knife blade cuts more easily than a dull one.

You also can think of a wedge that cuts objects in terms of how itchanges the pressure on a surface. The thin edges of a wedge provide asmaller surface area for the input force to act on. This greater pressuremakes it easier to break through the surface of an object. A sharpknife can cut through an apple skin, and a sharp chisel can applyenough pressure to chip stone.

A doorstop is a wedge that is used to hold objects together. To doits job, a doorstop is pressed tip-first under a door. As the doorstop is moved into position, it lifts the door slightly and applies a force tothe bottom of the door. In return, the door applies pressure to thedoorstop and causes the doorstop to press against the floor withenough force to keep the doorstop—and the door—from moving.

ScrewA is an inclined plane wrapped around a cylinder or cone toform a spiral. A screw is a simple machine that can be used to raiseand lower weights as well as to fasten objects. Examples of screwsinclude drills, jar lids, screw clamps, and nuts and bolts. The spiralinginclined plane that sticks out from the body of the screw forms thethreads of the screw.

In the photograph at right, a person is using a screwdriver, whichis a wheel and axle, to drive a screw into a piece of wood. Each turnof the screwdriver pushes the screw farther into the wood. As thescrew is turned, the threads act like wedges, exerting an output forceon the wood. If the threads are very close together, the force must beapplied over a greater distance—that is, the screw must be turnedmany times—but less force is needed.

The advantage of using a screw instead of a nail to hold thingstogether is the large amount of friction that keeps the screw fromturning and becoming loose. Think of pulling a nail out of a pieceof wood compared with pulling a screw from the same piece ofwood. The nail can be pulled straight out. The screw must be turnedthrough a greater distance to remove it from the wood.

Notice that the interior of the Guggenheim Museum shown onpage 164 is not only an inclined plane. It is also an example of a screw.The inclined plane is wrapped around the museum’s atrium, which isan open area in the center.

check your reading Explain how a screw moves deeper into the wood as it is turned.

screw

Screw

The mechanical advantage of a machine can be calculated.

Recall that the number of times a machine multiplies the input forceis the machine’s mechanical advantage. You can calculate a machine’smechanical advantage using this formula:

Mechanical Advantage = �OInu

ptp

uuttFFoorrccee

�

MA = �F

Fo

i

u

n

t�

This formula works for all machines, regardless of whether they aresimple machines or more complicated machines.

If a machine decreases the force you use to do work, the distanceover which you have to apply that force increases. It is possible to usethis idea to calculate the mechanical advantage of a simple machinewithout knowing what the input and output forces are. To make thiscalculation, however, you must assume that your machine is not losing any work to friction. In other words, you must assume thatyour machine is 100 percent efficient. The mechanical advantage thatyou calculate when making this assumption is called the idealmechanical advantage.

Inclined Plane You can calculate the ideal mechanical advantage of aninclined plane by dividing its length by its height.

Ideal Mechanical Advantage = �h

le

e

n

ig

g

h

th

t

o

o

f

f

i

i

n

n

c

c

l

l

i

i

n

n

e

e�

IMA = �hl�


lengthheight

reading tip

Scientists often consider the way in which an objectwill behave under ideal conditions, such as whenthere is no friction.


Be sure to use the length of the incline in your calculation, asshown in the diagram, and not the length of the base. If the mover inthe photograph on page 166 increased the length of the ramp, hewould increase the ramp’s mechanical advantage. However, he wouldalso increase the distance over which he had to carry the box.

Wheel and Axle To calculate the ideal mechanical advantage of awheel and axle, use the following formula:

Ideal Mechanical Advantage = �R

R

a

a

d

d

i

i

u

u

s

s

o

o

f

f

o

i

u

n

t

p

p

u

u

t

t�

IMA = �R

R

o

i

u

n

t�

The Ferris wheel below is a giant wheel and axle. A motor appliesan input force to the Ferris wheel’s axle, which turns the wheel. In thisexample, the input force is applied to the axle, so the radius of the axleis the input radius in the formula above. The output force is appliedby the wheel, so the radius of the wheel is the output radius.

For a Ferris wheel, the input force is greater than the output force.The axle turns through a shorter distance than the wheel does. Theideal mechanical advantage of this type of wheel and axle is less than 1.

Sometimes, as with a steering wheel, the input force is applied toturn the wheel instead of the axle. Then the input radius is the wheel’sradius, and the output radius is the axle’s radius. In this case, the inputforce on the wheel is less than the output force applied by the axle.The ideal mechanical advantage of this type of wheel and axle isgreater than 1.

SIMULATIONCLASSZONE.COM

Explore the mechanicaladvantage of an inclinedplane.

radius of axle

radius of wheel

reminder

The radius is the distancefrom the center of thewheel or axle to any pointon its circumference.


KEY CONCEPTS1. Name the six simple machines

and give an example of each.

2. Explain how a screw changesthe size of the force needed topush it into wood.

3. To calculate mechanical advantage, what two thingsdo you need to know?

CRITICAL THINKING4. Synthesize How is a pulley

similar to a wheel and axle?

5. Calculate What is the idealmechanical advantage of awheel with a diameter of 30 cm fixed to an axle with a diameter of 4 cm if the axleis turned?

CHALLENGE6. Infer How can you increase a

wedge’s mechanical advantage?Draw a diagram to show your idea.

Lever The beam balance above is a lever. The beam is the solid bar thatturns on a fixed point, or fulcrum. The fulcrum is the beam’s balancepoint. When you slide the weight across the beam, you are changingthe distance between the input force and the fulcrum. The mechanicaladvantage depends on the distances of the input force and output forcefrom the fulcrum. The output force is applied to balance the beaker.

To calculate the ideal mechanical advantage of a lever, use the following formula:

Ideal Mechanical Advantage =

IMA = �d

d

o

i

u

n

t�

This formula applies to all three arrangements of levers. If the distance from the input force to the fulcrum is greater than the distance from the output force to the fulcrum, the ideal mechanicaladvantage is greater than 1. The beam balance is an example of thistype of lever.

distance from input force to fulcrum��distance from output force to fulcrum

output forcefulcrum

input force

dout din


A Running MachineMarlon Shirley, who lives in Colorado, lost his lower left leg due to an accident at the age of five. He is a champion sprinter who achieved his running records while using a prosthesis (prahs-THEE-sihs), or a device used to replace a body part. Like his right leg, his prosthetic leg is a combination of simple machinesthat convert the energy from muscles in his body to move him forward. The mechanical system is designed to match the forces of his right leg.

Legs as LeversCompare Marlon Shirley’s artificial leg with his right leg. Both legshave long rods—one made of bone and the other of metal—thatprovide a strong frame. These rods act as levers. At the knee andankle, movable joints act as fulcrums for these levers to transferenergy between the runner’s body and the ground.

How Does It Work?1. As the foot—real or artificial—strikes the ground, the leg stops

moving forward and downward and absorbs the energy of thechange in motion. The joints in the ankle and knee act as fulcrums as the levers transfer the energy to the muscle in theupper leg. This muscle acts like a spring to store the energy.

2. When the runner begins the next step, the energy is transferredback into the leg from the upper leg muscle. The levers in theleg convert the energy into forward motion of the runner’s body.

The people who design prosthetic legs study the natural motion ofa runner to learn exactly how energy is distributed and convertedto motion so that they can build an artificial leg that works wellwith the real leg.

EXPLORE

1. VISUALIZE Run across a room, paying close attention tothe position of one of your ankles and knees as you move.Determine where the input force, output force, and fulcrum are in the lever formed by your lower leg.

2. CHALLENGE Use the library or the Internet to learn moreabout mechanical legs used in building robots that walk.How do the leg motions of these robots resemble yourwalking motions? How are they different?

PHYSICAL SCIENCE AND LIFE SCIENCE

Other parts of the humanbody can act like simplemachines. For example,teeth work like wedges.

RESOURCE CENTERCLASSZONE.COM

Find out more about artificial limbs.

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Sunshine StateSTANDARDSSC.C.2.3.4: The studentknows that simplemachines can be used tochange the direction orsize of a force.

VOCABULARYRemember to write a definition for compoundmachine in a word triangle.

BEFORE, you learned• Simple machines change the

size or direction of a force• All machines have an ideal

and an actual mechanicaladvantage

NOW, you will learn• How simple machines can

be combined• How scientists have developed

extremely small machines• How robots are used

KEY CONCEPT

Modern technology usescompound machines.

THINK ABOUT

How does a tow truck do work?

When a car is wrecked or disabled, the owner might call atowing service. The service sends a tow truck to take the car to berepaired. Tow trucks usually areequipped with a mechanism forfreeing stuck vehicles and towing, or pulling,them. Look at the tow truck in the photograph at the right. What simple machines do you recognize?

Compound machines are combinations of simple machines.

Like the tow truck pictured above, many of the more comple x devicesthat you see or use every day are combinations of simple machines.For example, a pair of scissors is a combination of two levers.The cutting edges of those levers are wedges. A fishing rod is a lever with the fishing line wound around a wheel and axle, the reel.A machine that is made of two or more simple machines is called a

In a very complex compound machine, such as a car, the simplemachines may not be obvious at first. However, if you look carefully at a compound machine, you should be able to identify forms oflevers, pulleys, and wheels and axles.

check your reading How are simple machines related to compound machines?

compound machine.

VOCABULARYcompound machine p. 170

nanotechnology p. 173robot p. 175


GearsGears are based on the wheel and axle. Gears have teeth on theedge of the wheel that allow one gear to turn another. A set ofgears forms a compound machine in which one wheel and axle islinked to another.

Two linked gears that are the same size and have the same numberof teeth will turn at the same speed. They will move in opposite directions. In order to make them move in the same direction, a thirdgear must be added between them. The gear that turns another gearapplies the input force; the gear that is turned exerts the output force.A difference in speed between two gears—caused by a difference insize and the distance each turns through—produces a change in force.

check your reading How do gears form a compound machine?

Mechanical Advantage of Compound MachinesThe mechanical advantage of any compound machine is equal to theproduct of the mechanical advantages of all the simple machines thatmake up the compound machine. For example, the ideal mechanicaladvantage of a pair of scissors would be the product of the idealmechanical advantages of its two levers and two wedges.

The mechanical advantage of a pair of gears with different diame-ters can be found by counting the teeth on the gears. The mechanicaladvantage is the ratio of the number of teeth on the output gear to thenumber of teeth on the input gear. If there are more than two gears,count only the number of teeth on the first and last gears in the sys-tem. This ratio is the mechanical advantage of the whole gear system.

Compound machines typically must overcome more friction than simple machines because they tend to have many moving parts.Scissors, for example, have a lower efficiency than one lever becausethere is friction at the point where the two levers are connected. There is also friction between the blades of the scissors as they close.

Gears

The gears in the photo-graph and diagram arespur gears, the most common type of gear.

reading tip

Micro-means “one-millionth.”For example, a microsecondis one-millionth of a second.Nano-means “one-billionth.”A nanosecond is one-billionthof a second.


Modern technology creates new uses for machines.

Sophisticated modern machinery is often based on or contains simplemachines. Consider Jaws of Life tools, which are used to help rescuepeople who have been in accidents. These cutters, spreaders, and rams are powered by hydraulics, the use of fluids to transmit force.When every second counts, these powerful machines can be used to pryopen metal vehicles or collapsed concrete structures quickly and safely.The cutters are a compound machine made up of two levers—muchlike a pair of scissors. Their edges are wedges.

Contrast this equipment with a drill-like machine so small that itcan be pushed easily through human arteries. Physicians attach the tinydrill to a thin, flexible rod and push the rod through a patient’s arteryto an area that is blocked. The tip rotates at extremely high speeds tobreak down the blockage. The tiny drill is a type of wheel and axle.

Microtechnology and NanotechnologyManufacturers make machines of all sizes by shaping and arrangingpieces of metal, plastic, and other materials. Scientists have used tech-nology to create very small machines through miniaturization—themaking of smaller and smaller, or miniature, parts. Micromachines aretoo small to be seen by the naked eye but are visible under a microscope.There is a limit, however, to how far micromachines can be shrunk.

To develop even tinier machines, scientists needed a newapproach. Scientists have used processes within the human body astheir model. For example, inside the body a protein molecule carries materials back and forth within a cell on regular paths that are similarto little train tracks. The natural machines in the human bodyinspired scientists to develop machines that could be 1000 timessmaller than the diameter of a human hair.

APPLY What simplemachines do you see in this Jaws of Life cutting tool?

These extremely tiny machines are products ofthe science and technology of building electronic circuits and devicesfrom single atoms and molecules. Scientists say that they create thesemachines, called nanomachines, from the bottom up. Instead ofshaping already formed material—such as metal and plastic—theyguide individual atoms of material to arrange themselves into theshapes needed for the machine parts.

Tools enable scientists to see and manipulate single molecules andatoms. The scanning tunneling microscope can create pictures ofindividual atoms. To manipulate atoms, special tools are needed toguide them into place. Moving and shaping such small units presentsproblems, however. Atoms tend to attach themselves to other atoms,and the tools themselves are also made of atoms. Thus it is difficult topick up an atom and place it in another position using a tool becausethe atom might attach itself to the tool.

check your reading Compare the way in which nanomachines are constructed withthe way in which larger machines are built.

Nanomachines are still mostly in the experimental stage. Scientistshave many plans for nanotechnology, including protecting computersfrom hackers and performing operations inside the body. For example,a nanomachine could be injected into a person’s bloodstream, whereit could patrol and search out infections before they become seriousproblems. When the machine had completedits work, it could switch itself off and be passed out of the body. Similarnanomachines could carry anti-cancerdrugs to specific cells in the body.

Nanotechnology could also be used todevelop materials that repel water and dirtand make cleaning jobs easy. Nanoscale biosensors could be used to detect harmful substances in the environ-ment. Another possible use fornanotechnology is in military uniforms that can change color—the perfect camouflage.

In the future, nanotechnologymay change the way almost every-thing is designed and constructed.As with any new technology, it will be important to weigh both the potential risks and benefits.

nanotechnology, RESOURCE CENTERCLASSZONE.COM

Learn more aboutnanomachines.

This microgear mechanismcould be used in a micro-machine that includesmicroscopic sensors andtiny robots.


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Scientists are using a robot to unlock the secrets of the Great Pyramid in Egypt.

A Robot at Work

second doorminiature camera

Pyramid Rover body

computer

first door

The frame of the Pyramid Rover is 12 centimeters(about 5 in.) wide and 30 centimeters (about 1 ft)long. As it moves, it uses two sets of flexibletreads to grip the top and bottom of the narrowshafts inside the pyramid. The robot is linked to a computer by a fiber-optic cable.

Queen’s Chamber

entrance

shaft explored by Pyramid Rover


What simple machines do you think might be part of the Pyramid Rover?


RobotsHumans have always taken risks to do jobs in places that are dangerousor difficult to get to. More and more often, robots can be used to dothese jobs. A is a machine that works automatically or byremote control. When many people hear the word robot, they think ofa machine that looks or moves like a person. However, most robots donot resemble humans at all. That is because they are built to do thingshumans cannot do or to go places where it is difficult for humans to go.

The Pyramid Rover, shown on page 174, is an example of a robotdeveloped to go where people cannot. After a camera revealed a doorat the end of an eight-inch-square shaft inside the Great Pyramid, thePyramid Rover was sent through the shaft to explore the area.While researchers remained in the Queen’s Chamber in the center ofthe pyramid, the robot climbed the shaft until it came to a door.Using ultrasound equipment mounted on the robot, researchersdetermined that the door was three inches thick. The robot drilled ahole in the door for a tiny camera and a light to pass through.The camera then revealed another sealed door!

Many companies use robots to manufacture goods quickly andefficiently. Robots are widely used for jobs such as welding, painting,and assembling products. Robots do some repetitive work better thanhumans, because robots do not get tired or bored. Also, they do thetask in exactly the same way each time. Robots are very important tothe automobile and computer industries.

check your reading How are robots better than humans at some jobs?

robot

KEY CONCEPTS1. How do you estimate the

mechanical advantage of acompound machine?

2. What are some uses of nanotechnology? Can youthink of other possible uses for nanomachines?

3. What are three types of jobsthat robots can do?

CRITICAL THINKING4. Synthesize What factors

might limit how large or howsmall a machine can be?

5. Infer How do you think thesize of a gear compared withother gears in the same systemaffects the speed of its rotation?

CHALLENGE6. Apply Robots might be put

to use replacing humans infirefighting and other danger-ous jobs. Describe a job that isdangerous. Tell what a robotmust be able to do and whatdangers it must be able to withstand to accomplish therequired tasks.

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CHAPTER INVESTIGATIONCHAPTER INVESTIGATION

Design a MachineOVERVIEW AND PURPOSEAlthough simple machines were developed thousands of yearsago, they are still used today for a variety of purposes. Tasks suchas cutting food with a knife, using a screwdriver to tighten ascrew, and raising a flag on a flagpole all require simple machines.Activities such as riding a bicycle and raising a drawbridge makeuse of compound machines. In this investigation you will usewhat you have learned about simple and compound machines to

• choose a machine to design• build your machine, test it, and calculate its mechanical

advantage and efficiency

Make a data table like the one shown on page 177.

From among the three choices listed below, choose which problem you are going to solve.

Carnival Game You work for a company that builds carnivalgames. Your supervisor has asked you to build a game in whicha simple machine moves a 500-gram object from the bottom ofthe game 1 meter up to the top. This simple machine can bepowered only by the person operating the game.

Video Game Contest The marketing department of a videogame company is holding a contest. Candidates are asked to submit a working model of a compound machine that will movea 500-gram object a distance of 1 meter. The winning design willbe used in a new video game the company hopes to sell. Thiscompound machine must include at least 2 simple machines.

Construction Company You work for a construction company. Your boss has asked you to design amachine for lifting. Your first step is to build a scale model. The modelmust be a compound machine with amechanical advantage of 5 that canmove a 500-gram object a distance of1 meter. You also can use a 100-gramobject in your design.

Procedure

MATERIALS• 500 g object• 100 g object• meter stick• spring scale• pulleys with rope• board• stick or pole


Brainstorm design ideas on paper. Think of different types of machines you might want to build. Choose one machine to build.

Build your machine. Use your machine to perform the task of moving a 500-gram object a distance of 1 meter.

If you chose the third problem, test your compound machine to determine if it has a mechanical advantage of 5. If not, modify your machine and retest it.

Record all measurements in your data table.

1. RECORD OBSERVATIONS Make asketch of your machine.

2. CALCULATE Use your data to calculatethe mechanical advantage and efficiency ofyour machine. Use the formulas below.

Mechanical Advantage = �OInuptpuuttFFoorcrece

�

Efficiency (%) = �WW

oorrkkoiun

t� p 100

3. ANALYZE

Carnival Game Add arrows to the drawingof your machine to show the forces involvedand the direction of those forces. If your goalwas to move the ball from the top of thegame to the bottom at a constant speed,how would your machine and diagram haveto be changed?

Video Game Contest Does your machinechange the size of the force, the direction of the force, or both? If you used a pulleysystem (two or more pulleys working together),describe the advantages of using such a system.

Construction Company Determine whetherforce or distance is changed by each simplemachine in your compound machine. In whatways might you improve your machine toincrease its efficiency?

1. INFER How might changing the arrange-ment of the parts in your machine affect themachine’s mechanical advantage?

2. IDENTIFY LIMITS What was the hardest part about designing and constructingyour machine?

3. APPLY If you needed to lift a large rockfrom a hole at a construction site, which typeof simple machine would you use and why?Which type of compound machine would be useful?

CHALLENGE If you made a simple machine,how would you combine it with another simplemachine to increase its mechanical advantage?

If you made a compound machine, redesign it toincrease its efficiency or mechanical advantage.What made the difference and why?

Draw a plan for the new machine. Circle theparts that were changed. If you have time, buildyour new machine.

INVESTIGATE Further

ConcludeWriteIt Up

Observe and AnalyzeWriteIt Up

Design a Machine

Observe and Analyze

Table 1. Machine Data

Sketch

Output force Input force Mechanical

Advantage

Output work Input work Efficiency



Content Review andFCAT practice

1

2

3

4

5.1

5.2

5.3

178 Unit 1: Motion and Forces

Machines help people do work by changing the force applied to an object.

KEY CONCEPTS SUMMARY

VOCABULARYmachine p. 151mechanical advantage p. 153

efficiency p. 156

VOCABULARYsimple machine p. 160lever p. 161fulcrum p. 161wheel and axle p. 162pulley p. 162inclined plane p. 164wedge p. 164screw p. 165

VOCABULARYcompound machine p. 170

nanotechnology p. 173robot p. 175

Six simple machines have many uses.Simple machines change the size and/or direction of a force.

Chapter Review

changes direction changes bothchanges size

fulcrum

inputforce

outputforce

Machines help people do work.When you use a machine to do work, there is always an exchange, or tradeoff,between the force you apply and the distance over which you apply that force.

Modern technology uses compound machines.• Compound machines are combinations of simple machines.• Modern technology creates new uses for machines, as in

microtechnology, nanotechnology, and robots.

Forces can cause change.• Forces can change motion.

• Work is force applied over a distance.

• Forces can transfer energy bydoing work.

Average speed = �dis

ttiamnece

� v– = �dt�

Work = Force p distance W = Fd

VOCABULARYforce p. 143motion p. 144speed p. 145work p. 149

1

2

3

4


Content Review andFCAT practice

input force

output force

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Reviewing Key Concepts

Multiple Choice Choose the letter of the bestanswer.

16. Angela walks 300 meters in 100 seconds.What is her speed?

a. 300 m/s c. 3 m/s

b. 30 m/s d. 0.3 m/s

17. You lifted a weight 1 meter. You friend liftedthe same weight 2 meters. Your friend

a. did twice the work you did

b. did the same work you did

c. did half the work you did

d. did no work

18. To calculate mechanical advantage, you needto know

a. time and energy

b. input force and output force

c. distance and work

d. size and direction of a force

19. A machine in which the input force is equal tothe output force has a mechanical advantage of

a. 0 c. 1

b. between 0 and 1 d. more than 1

20. You can increase a machine’s efficiency by

a. increasing force c. increasing distance

b. reducing work d. reducing friction

21. When you bite into an apple, your teeth act aswhat kind of simple machine?

a. lever c. wedge

b. pulley d. screw

Short Response Write a short response to eachquestion.

22. Describe the simple machines that make up scissors.

23. How do you calculate the mechanical advantage of a compound machine?

24. How did scientists use processes inside the human body as a model for makingnanomachines?

Reviewing Vocabulary

Write the name of the simple machine shownin each illustration. Give an example from real life for each one.

Copy the chart below, and write a definitionof each term in your own words. Use themeaning of the term’s root to help you.

Write a sentence describing the relationshipbetween each pair of terms.

14. motion, speed

15. force, work

1.

2.

3.

4.

5.

6.

Term Root Meaning Definition

7. machine having power

8. nanotechnology one-billionth

9. simple machine basic

10. efficiency accomplishing

11. compound put togethermachine

12. robot work

13. fulcrum to support

180 Unit 1: Motion and Forces

Thinking Critically

25. SYNTHESIZE A bowl is on a table. Some timelater, the bowl is in the same place. Can youtell if the bowl has moved? Why or why not?

26. INFER Which simple machine would you use to raise a very heavy load to the top of a building? Why?

27. INFER A car with a speed of 30 km/h slowsdown to 20 km/h. Was there a force acting on the car? How do you know?

28. APPLY You are using a board to pry a largerock out of the ground when the board sud-denly breaks apart in the middle. You pick uphalf of the board and use it to continue pryingup the rock. The fulcrum stays in the sameposition. How has the mechanical advantageof the board changed? How does it changeyour work?

29. ANALYZE Dan pushes an empty box across the floor. Jonathan stands still, holding a veryheavy box in his arms. Who is doing morework, and why?

Use the information in the diagram below toanswer the next three questions.

30. SYNTHESIZE What is the mechanical advantageof the ramp? By how many times does theramp multiply the man’s input force?

31. INFER If the ramp’s length stayed the same butthe height was raised, how would this changethe input force required?

32. ANALYZE If the man pushed the box along theramp instead of carrying it, would he need toapply a greater or a smaller force to get thebox into the truck? Explain.

1.5 m

4 m

Using Math Skills in Science

Complete the following calculations.

33. Yuliya ran 100 m in 11 s. What was herspeed?

34. Alyse lifted a box from the floor to a shelf thatwas 2.5 m high. If she used a force of 100 Nto lift the box, how much work did she do?

35. You swing a hockey stick with a force of 10 N.The stick applies 5 N of force on the puck.What is the mechanical advantage of thehockey stick?

36. Your input work on a manual lawn mower is125,000 J. The output work is 90,000 J. What is the efficiency of the lawn mower?

37. A steering wheel has a radius of 21 cm. The steering column on which it turns has a radius of 3 cm. What is the mechanicaladvantage of this wheel and axle?

38. Two gears with the same diameter form a gearsystem. Each gear has 24 teeth. What is themechanical advantage of this gear system?

39. DRAW CONCLUSIONS Look back at the photo-graph on pages 140–141. Name the simplemachines you see in the photograph. How doyou think they work together to move ballsthrough the sculpture? How has your under-standing changed as to the way in whichmachines help people work?

40. SYNTHESIZE Think of a compound machine you have used recently. Explain which simplemachines it includes and how they helped you do work.

41. PREDICT How do you think nanotechnology willbe useful in the future? Give several examples.

Evaluate all of the data, results, and informationfrom your project folder. Prepare to present yourproject to the class. Be ready to answer questionsposed by your classmates about your results.

FCAT Practice FLORIDA REVIEWCLASSZONE.COM

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Analyzing GraphicsThe Archimedean screw is a mechanical device first used more than2000 years ago. It consists of a screw inside a cylinder. One end of thedevice is placed in water. As the screw is turned with a handle, itsthreads carry water upward. The Archimedean screw is still used in someparts of the world to pump water for irrigating fields. It can also be usedto move grain in mills.

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When answering a short-response question, try notto leave the answer spaceblank. Show your work andwrite down your thoughts,even if you don’t give acomplete answer; partialcredit is awarded for thistype of question.

FCAT

Study the illustration of an Archimedean screw. Then answer the questions that follow.

MULTIPLE CHOICE1. Which type of simple machine moves water in

the cylinder?

A. block and tackle C. screw

B. pulley D. wedge

2. Which type of simple machine is the handle?

F. wheel and axle

G. inclined plane

H. pulley

I. wedge

3. What is the energy source for the Archimedeanscrew?

A. the water pressure inside the screw

B. the person who is turning the handle

C. falling water that is turning the screw

D. electrical energy

4. How is the Archimedean screw helping the personin the illustration do work?

F. by decreasing the input force needed to lift thewater

G. by decreasing the work needed to lift the water

H. by decreasing the distance over which the inputforce is applied

I. by keeping the water from overflowing itsbanks

SHORT RESPONSE5. A person using an Archimedean screw with

threads that are closer together must turn thehandle more times with less effort. Explain why aperson using this type of Archimedean screw hasto turn the handle more times.

EXTENDED RESPONSE

Answer the two questions below in detail.

6. A playground seesaw is an example of a lever. The fulcrum is located at the center of the board.People seated at either end take turns applying the force needed to move the other person. If oneperson weighs more than the other, how can theyoperate the seesaw? Consider several possibilitiesin your answer.

7. Picture two gears of different sizes turning together.Suppose you can apply a force to turn the largergear or the smaller gear, and it will turn the other.Discuss what difference it would make whetheryou turned the larger or smaller gear. Describe theinput work you would do on the gear you areturning and the output work that gear would doon the other gear.

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