Lesson 3 Simple Machines

Lesson 3 | Simple Machines Student Labs and Activities Page 48 Content Vocabulary 49 Lesson Outline 50 MiniLab 52 Content Practice A 53 Cont...
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Lesson 3 | Simple Machines Student Labs and Activities

Page 48

Content Vocabulary

49

Lesson Outline

50

MiniLab

52

Content Practice A

53

Content Practice B

54

Language Arts Support

55

School to Home

57

Key Concept Builders

58

Enrichment

62

Challenge

63

Lab A

66

Lab B

69

Lab C

72

Chapter Key Concepts Builder

73

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Launch Lab

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Launch Lab

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LESSON 3: 15 minutes

How does a lever work? Humans have used levers for thousands of years to make work easier. How does a lever change the force applied to it?

Procedure 1. Read and complete a lab safety form. 2. Place a ruler on top of an eraser, as shown in your textbook. Place a book on one end of the ruler.

3. Lift the book by pushing down on the other end of the ruler. Record in the

Data and Observations section below how easy or difficult it is to lift the book.

4. Repeat steps 2 and 3 several times using different locations of the eraser along the ruler.

Data and Observations

1. Explain how changing the position of the eraser affected the force exerted by the lever.

2.

Key Concept How would you describe the motion of the lever? Is the motion of the lever simple or complicated? Explain.

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Think About This

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Content Vocabulary

LESSON 3

Simple Machines Directions: Complete the chart by providing at least one example for each item below.

Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Give an example of . . .

Examples

a simple machine.

1.

an inclined plane.

2.

a lever.

3.

something that acts as a fulcrum.

4.

something a screw is used to do.

5.

a wheel and axle.

6.

a wedge.

7.

a pulley.

8.

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Lesson Outline

LESSON 3

Simple Machines A. What is a simple machine? 1. A(n)

is a machine that does work using only one

movement.

2. These machines do work in a(n)

motion.

B. Levers 1. A(n)

is a simple machine made of a bar that pivots or

rotates about a fixed point.

2. The point that a lever pivots on is called a(n)

.

3. The distance from the fulcrum to the input force is the ; the distance from the fulcrum to the output force is the

.

4. With a first-class lever, the fulcrum is

the input force

and the output force.

5. With a second-class lever, the

force is between the

force and the fulcrum. force is between the force and the fulcrum.

7. The ideal

of a lever equals the length of the input arm divided by the length of the output arm.

a. The mechanical advantage of a(n)

-class lever can

vary, depending on the location of the fulcrum.

b. In a second-class lever, the the

arm is always longer than arm.

c. In a third-class lever, the the

arm is always shorter than arm.

8. In the human body,

provide force for the levers.

a. The neck is a(n)

-class lever, with the neck muscles

providing the

force.

b. The foot is a(n)

-class lever, and the arm is a(n) -class lever.

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6. With a third-class lever, the

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Lesson Outline continued C. Wheel and Axle 1. A(n)

is an axle attached to the center of a wheel and

both rotate together.

2. For a wheel and axle, the length of the input arm is the of the wheel; the length of the output arm is the the axle.

of

D. Inclined Planes 1. A(n)

is a flat, sloped surface.

2. The ideal mechanical advantage of an inclined plane is the of the inclined plane divided by its

.

3. A sloped surface that moves is called a(n)

.

4. A(n)

is an inclined plane wrapped around a cylinder.

5. A(n)

is a simple machine that is a grooved wheel with a

rope or cable wrapped around it.

6. A(n)

pulley only changes the direction of the force.

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7. A(n)

pulley decreases the force but increases the distance over which the force acts.

8. The ideal mechanical advantage of a pulley is equal to the number of of rope pulling up on the object.

E. What is a compound machine? 1. Two or more simple machines that operate together form a(n) machine.

2. A(n)

is a wheel and axle that has teeth around

the wheel.

3. When the teeth of two or more gears

, the turning of

one gear makes the other(s) turn.

4. The speed and force of gears is affected by the

of

the gears.

5. The efficiency of a compound machine is determined by the efficiency of each component machine together.

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MiniLab

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LESSON 3: 20 minutes

Can you increase mechanical advantage? Pulley systems change the size and the direction of an applied force. How can you change the mechanical advantage of a pulley system?

Procedure 1. Read and complete a lab safety form. 2. Use two broomsticks and an 8-m length of rope to make a pulley system, as shown in your textbook. Hold each broomstick waist-high. Tie the rope to one of the broomsticks and loop it around the other.

3. Have a student pull the free end of the rope, as shown in your textbook. Record in the space below the forces acting on the broomsticks.

4. Take the excess rope and make two more loops around the broomsticks. Repeat step 3.

Data and Observations

1. Describe how the force applied on the broomsticks changed when the number of loops in the pulley system increased.

2.

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Key Concept Relate the number of rope segments used in each pulley system to the mechanical advantage of each system.

Work and Simple Machines

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Analyze and Conclude

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Content Practice A

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LESSON 3

Simple Machines Directions: On the line before each statement, write T if the statement is true or F if the statement is false.

1. There are a total of three types of simple machines. 2. A lever consists of a bar that pivots about a fixed point called the focus. 3. There are four classes, or kinds, of levers. 4. The mechanical advantage of a second-class lever is always less than 1. 5. The forearm of the human body works like a third-class lever. 6. The length of a wheel’s input arm is the diameter of the wheel. 7. The purpose of a ramp, which is a type of inclined plane, is to make it easier to

Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

move a heavy object over a vertical distance.

8. A wedge is a sloped surface that forces materials apart. 9. When you turn a screw into a piece of wood, the input force of the screwdriver is converted to an output force by the threads of the screw.

10. A combination of fixed and movable pulleys working together is called a pulley system.

11. When two or more simple machines work together, it is called a composite machine.

12. The efficiency of such a machine is determined by multiplying the efficiencies of each simple machine.

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Content Practice B

LESSON 3

Simple Machines Directions: Answer each question on the lines provided.

1. What is a simple machine, and what are the six types of simple machines?

2. Which factors determine whether a lever is a first-class lever, second-class lever, or third-class lever?

3. How does the MA of a 6-m ramp compare with the MA of a 4-m ramp if both are used

4. What is a compound machine?

5. How does the input force applied by a large gear change when the force is applied to a smaller gear?

6. How do you calculate the overall efficiency of a compound machine?

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to load crates onto trucks that have cargo areas that are 1 m off the ground?

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Language Arts Support

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LESSON 3

Language-Usage Activity: Using Its and It’s A common error in writing is using the word it’s when the correct word is its. Its is the possessive form, meaning “belonging to it.” The model of the mountain did not match its actual shape. It’s is a contraction of the word it and the word is. It is wider in the middle. It’s wider in the middle. If you are unsure of which word to use, substitute it is in the sentence. If it makes sense, use it’s.

Practicing the Skill Directions: Circle the correct form of the word that completes each sentence.

1. You probably have heard of a seesaw. (It’s/Its) one of three kinds of levers. 2. A first-class lever has (its/it’s) fulcrum between the input force and the output force.

Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

3. For a second-class lever, (its/it’s) location is different. The output force is between the fulcrum and the input force.

4. A piece of luggage that has wheels is a second-class lever. (It’s/Its) easier to roll luggage than to carry it.

5. Do you know where the input force is applied in a third-class lever? (Its/It’s) between the fulcrum and the output force.

6. I have used a shovel, and (its/it’s) the same as using a third-class lever.

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Language Arts Support

LESSON 3

Language-Usage Activity: Subject-Verb Agreement Verbs and their subjects must agree in number. Singular Subjects

Plural Subjects

A lever is a simple machine. Subject: lever—singular Verb: is—singular

Levers and wedges are simple machines. Subject: Levers and wedges—plural Verb: are—plural

In the present tense, verbs with the subject he, she, or it must end with –s. To test whether the subject and verb agree:

1. Find the subject of the sentence. 2. Ask yourself whether the subject is singular or plural. 3. Find the verb in the sentence. 4. Ask yourself whether the verb is in the singular or plural form. If the subject and verb are both singular or both plural, they agree. The –s Rule: In general, if the subject ends in –s, the verb cannot end in –s. The dog barks.

The dogs bark.

Directions: Write YES on the line before each sentence if its subject and verb agree. Write NO if the subject and verb do not agree. If the subject and verb do not agree, write the correct form of the verb on the line after each sentence.

1. Your front tooth is an example of a wedge. 2. An axe also works as a wedge. 3. The fulcrum are the pivot point of the lever. 4. Two forces acts on a lever—the input force and the output force.

5. Your forearm work like a third-class lever. 6. Six types of simple machines are used. 7. The lengths of the input and output arms are important for calculating the ideal mechanical advantage of a lever.

8. When you turn a screw, the output force pull the screw into the material.

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Applying the Skill

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School to Home

LESSON 3

Simple Machines Did you know? Simple machines fall into two categories—the wedge family and the lever family. The wedge family includes the wedge, screw, and inclined plane. Screws and inclined planes are a variation on wedges. The lever family includes the lever, pulley, and wheel and axle. Pulleys and wheel and axles are a variation on levers. For this activity, list three examples of each type of simple machine that you might see in your home or neighborhood.

Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

Simple Machine

Example 1

Example 2

Example 3

1. Wedge

a.

b.

c.

2. Screw

a.

b.

c.

3. Inclined plane

a.

b.

c.

4. Lever

a.

b.

c.

5. Pulley

a.

b.

c.

6. Wheel and axle

a.

b.

c.

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Key Concept Builder

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LESSON 3

Simple Machines Key Concept What is a simple machine? Directions: On the line before each item, write L if it uses or is a lever, WH if it uses or is a wheel and axle, I if it uses or is an inclined plane, WE if it uses or is a wedge, S if it uses or is a screw, or P if it uses or is a pulley.

1. flagpole 2. wedge that splits wood 3. roller skates 4. crowbar 5. jar lid 6. nail 7. sailboat mast Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

8. truck-loading ramp 9. seesaw 10. doorknob 11. drill bit 12. nutcracker 13. wheelchair ramp 14. narrow bow of a ship Directions: Define simple machine on the lines provided.

15.

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Key Concept Builder

LESSON 3

Simple Machines Key Concept What is a simple machine? Directions: On the line before each definition, write the letter of the term that matches it correctly. Each term is used only once.

1. a lever’s pivot point

A. first-class lever B. screw

2. a shaft that turns

C. second-class lever D. pulley

3. a wheelbarrow

E. wedge F. fulcrum

4. the part of a lever that applies force 5. a flat, sloped surface

G. input arm H. third-class lever I. inclined plane

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6. a sloped surface that moves

J. axle

7. a hockey stick 8. an inclined plane wrapped around a cylinder 9. an oar 10. good for vertical lifting

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Key Concept Builder

LESSON 3

Simple Machines Key Concept How is the ideal mechanical advantage of simple machines calculated? Directions: Use the equations to answer each question on the lines provided.

1. What is the mechanical advantage of a lever that has an output arm measuring 0.5 m and an input arm measuring 1.5 m?

length of input arm (in meters) mechanical advantage of a lever = _______________________

length of output arm (in meters) L

in MA = ____ L

out

2. What is the mechanical advantage of a wheel that has a radius of 0.35 m, if the axle has a radius of 0.05 m?

radius of axle (in meters) r______ MA = wheel raxle

3. What is the mechanical advantage of a ramp with a length of 5 m and a height of 1 m?

length of inclined plane (in meters) mechanical advantage of an inclined plane = _________________________

height of inclined plane (in meters)

l MA = __ h

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radius of wheel (in meters) mechanical advantage of a wheel and axle = ___________________

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LESSON 3

Simple Machines Key Concept How are simple machines and compound machines different? Directions: Answer each question on the lines provided.

1. What is a compound machine?

2. How is the efficiency of a compound machine calculated?

3. What happens to the efficiency of the overall machine as more simple machines are

Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

added to it?

4. How can gears change the size and direction of a force?

5. Explain why a wedge that splits wood is an example of a compound machine.

6. Suppose the efficiency of the wedge portion of a wedge that splits wood is 90 percent (or 0.9) and the efficiency of the lever part of it is 80 percent (or 0.8). What is the efficiency of the machine?

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Enrichment

LESSON 3

Sharks and Levers Bethany Hamilton is a courageous teenage girl who is a competitive surfer. In 2003, when she was 13 years old, Bethany lost her left arm in a shark attack near her home in Hawaii. Three weeks later she was back in the water and later returned to competitive surfing and other sports with her one good arm. She was fitted with an artificial arm made of graphite and silicon.

Body Levers

Figure 1 Bicep muscle

One type of prosthesis, the myoelectric arm, uses small electric motors to move the replaced limb. When a muscle in the body contracts, or flexes, a small electric signal is created in the body and sent to a controller that switches the motors in the hand, wrist, and elbow on or off to produce movement and function. Disadvantages of this type of prosthesis are the inconvenience of a battery and severe damage to the motors and controller from water exposure. Developed in 2008, a next generation prosthetic arm is called the Luke arm. This device attaches to nerves and decodes the signals that tell an arm, wrist, hand, and fingers what to do. When a person uses the Luke arm with an interface, he or she merely thinks about taking a drink of water, and sensors pick up and interpret electric impulses that tell the arm to perform the necessary actions. Figure 2 shows a prototype of the Luke arm. Luke arm prosthesis Figure 2 D C

Soft drink

Elbow pivot

Applying Critical-Thinking Skills Directions: Respond to each statement.

B

A

1. Predict what will happen when the bicep muscle exerts force on the lower arm bone in Figure 1.

2. Describe the location of the fulcrum and the location of the load in Figure 2. 62

Work and Simple Machines

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Devices such as prosthetic arms are possible because the human skeleton can be thought of as a system of bony levers. In the body, levers of bone are activated by muscles that produce movement. These principles of biomechanics are applied to the design of prosthetic arms and legs. Figure 1 illustrates the arm as a thirdclass lever that has the fulcrum at the elbow, the force at the lower muscle connection, and the load in the hand. When the muscle pulls upward on the bone, the arm moves at the elbow, and the hand lifts the load.

Prosthesis Types

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LESSON 3

Simple Machines and Your Day We use simple machines every day—levers, wedges, pulleys, inclined planes, screws, and wheels and axles. Look around and see where they are. Some simple machines are easy to identify, but some might surprise you.

Observe and Describe Simple Machines Throughout a day at home or in school, identify five simple machines that you use.

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Now choose one machine and draw a diagram of that machine in use. Describe how the machine operates. Indicate whether it is a lever, wedge, pulley, inclined plane, screw, or wheel and axle.

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Lab A

40 minutes

Comparing Two Simple Machines You will use a pulley and an inclined plane to lift a 250-g mass to a height of 20 cm. Which simple machine makes the work of lifting the load the easiest?

Question Will the pulley or the inclined plane have a greater mechanical advantage?

Materials 250-g hanging mass

5-N spring scale

ring stand

meterstick

small pulley

Also needed: 50-cm × 15-cm board, books, 2-m length of heavy string

Safety Procedure 1. Read and complete a lab safety form. 2. Examine the equipment and diagrams. With your group, discuss why each simple machine has a mechanical advantage when lifting the mass. advantage in lifting the mass. Record your prediction.

4. What data will you need to collect to calculate mechanical advantage?

Use the data table. Add labels for the data you plan to collect to calculate mechanical advantage for each type of the simple machine. Pulley

Inclined Plane

Weight:

Length:

Force:

Height:

66

:

:

:

:

Work and Simple Machines

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3. Predict whether the pulley or the inclined plane will provide the greatest mechanical

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Lab A continued 5. Use the spring scale to measure the weight of the 250-g mass. Record the weight in newtons.

6. Set up the pulley and the ring stand as shown in your textbook. Adjust the spring scale and the pulley so that the weight just clears the table. Use the spring scale to slowly lift the weight to a height of 20 cm on the meterstick. Record the force in newtons in your data table. Repeat.

7. Set up the inclined plane as shown in your textbook so the top of the ramp is 20 cm above the table. Attach the spring scale to the weight. Beginning at the bottom of the ramp, use the spring scale to pull the weight steadily up the ramp. Record the force in newtons in your data table.

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Repeat.

Lab Tips • A moveable pulley supports part of the weight, allowing less force to be used to lift the object. • The ideal mechanical advantage of an inclined plane is the length of the ramp divided by the height of the ramp.

Analyze and Conclude 8. Interpret Data What is the mechanical advantage of the pulley and the inclined plane? Was your hypothesis correct? Explain.

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Lab A continued 9. Explain What other measurements would you need in order to calculate the efficiency of each machine?

Remember to use scientific methods. Make Observations Ask a Question Form a Hypothesis Test your Hypothesis

10.

The Big Idea Did the amount of work done on the weight to lift it to a height of 20 cm change with each machine? Explain. Did the machines make doing the work easier?

Analyze and Conclude Communicate Results

Communicate Your Results

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Make a large data table on which all groups can display their data. Discuss similarities and differences between group data.

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Lab B

Class

40 minutes

Comparing Two Simple Machines You will use a pulley and an inclined plane to lift a 250-g mass to a height of 20 cm. Which simple machine makes the work of lifting the load the easiest?

Question Will the pulley or the inclined plane have a greater mechanical advantage?

Materials 250-g hanging mass

5-N spring scale

ring stand

meterstick

small pulley

Also needed: 50-cm × 15-cm board, books, 2-m length of heavy string

Safety Procedure 1. Read and complete a lab safety form. 2. Examine the equipment and diagrams. With your group, discuss why each simple machine has a mechanical advantage when lifting the mass.

3. Predict whether the pulley or the inclined plane will provide the greatest mechanical Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

advantage in lifting the mass. Record your prediction.

4. Make a data table with rows for the data you plan to collect to calculate mechanical advantage for each type of the simple machine.

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Lab B continued 5. Use the spring scale to measure the weight of the 250-g mass. Record the weight in newtons.

6. Set up the pulley and the ring stand as shown in your textbook. Adjust the spring scale and the pulley so that the weight just clears the table. Use the spring scale to slowly lift the weight to a height of 20 cm. Record the force in newtons. Repeat.

7. Set up the inclined plane as shown in your textbook so that the top of the ramp is 20 cm above the table. Attach the spring scale to the weight. Beginning at the bottom of the ramp, use the spring scale to pull the weight steadily up the ramp. Record the force in newtons. Repeat.

Lab Tips • A moveable pulley supports part of the weight, allowing less force to be used to lift the object. • The ideal mechanical advantage of an inclined plane is the length of the ramp divided by the height of the ramp.

Analyze and Conclude 8. Interpret Data What is the mechanical advantage of the pulley and the inclined plane? Was your hypothesis correct? Explain. Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.

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Lab B continued 9. Explain What other measurements would you need in order to calculate the efficiency of each machine?

Remember to use scientific methods. Make Observations Ask a Question

10.

The Big Idea Did the amount of work done on the weight to lift it to a height of 20 cm change with each machine? Explain. Did the machines make doing the work easier?

Form a Hypothesis Test your Hypothesis Analyze and Conclude Communicate Results

Communicate Your Results

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Make a large data table on which all groups can display their data. Discuss similarities and differences between group data.

Extension How can you increase the mechanical advantage of your inclined plane? To investigate your question, design a controlled experiment.

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Lab C

Increasing Mechanical Advantage Directions: Use the information and data from the Lab B Comparing Two Simple Machines to perform this lab.

In Lab B, you used a pulley and an inclined plane to lift a 250-g mass to a height of 20 cm. You discovered, through your experiment, which simple machine makes the work of lifting the load the easier. Now, use what you know to increase the mechanical advantage of your inclined plane. Please note that you must complete Lab B before beginning Lab C. Also, have your teacher approve your design and safety procedures before beginning your experiment.

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Chapter Key Concepts Builder

Work and Simple Machines End-of-Chapter Practice Directions: Answer each question on the lines provided.

1. When a force is applied to an object, what must occur for work to be accomplished on the object?

2. What is the unit of power, and what is the equation for calculating power?

3. How does a machine convert input work to output work?

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4. What is a machine’s mechanical advantage, and how is it calculated?

5. Why is the efficiency of a machine always less than 100 percent?

Directions: Work with a partner. Select one of the options. When you have finished, present your results to the class.

6. Choose a simple machine and at least ten real-world applications of it. Locate a photograph or illustration of each use and create a pictorial presentation with captions.

7. Learn how a block-and-tackle pulley system works. Determine a few ways that this compound machine has been used throughout history. Locate photos and illustrations of the applications that you include and write captions to go with them.

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