motion and momentum - pc\|macimages.pcmac.org/sisfiles/schools/al/jacksoncounty...20 motion and...

$: Motion and Momentum - PC\|MACimages.pcmac.org/SiSFiles/Schools/AL/JacksonCounty...20 Motion and Momentum Section 1 What is motion? Section 2 Acceleration Directions: Circle the term$
Glencoe Science

Chapter Resources

Motion and Momentum

Includes:

Reproducible Student Pages

ASSESSMENT

✔ Chapter Tests

✔ Chapter Review

HANDS-ON ACTIVITIES

✔ Lab Worksheets for each Student Edition Activity

✔ Laboratory Activities

✔ Foldables–Reading and Study Skills activity sheet

MEETING INDIVIDUAL NEEDS

✔ Directed Reading for Content Mastery

✔ Directed Reading for Content Mastery in Spanish

✔ Reinforcement

✔ Enrichment

✔ Note-taking Worksheets

TRANSPARENCY ACTIVITIES

✔ Section Focus Transparency Activities

✔ Teaching Transparency Activity

✔ Assessment Transparency Activity

Teacher Support and Planning

✔ Content Outline for Teaching

✔ Spanish Resources

✔ Teacher Guide and Answers

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Motion and Momentum 19

Directions: Complete the concept map using the terms in the list below.

meters per second momentum kilograms velocity

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Directed Reading for

Content Mastery

OverviewMotion and Momentum

Directions: Write the letters of the words or phrases that correctly answer the following questions.

5. Which of the following are objects in motion?

a. rose bush c. both a and bb. puddle of water d. neither a or b

6. When something is in motion it is changing ______.

a. location c. both a and bb. mass d. neither a or b

Directions: Answer the following questions on the lines provided.7. What is happening to an object when it has a negative acceleration?

8. If a moving object speeds up, in what direction is the acceleration?

and

which is measured in which is indicated by

is the productof an object’s

mass

1.

2.

3. 4.

Name Date Class

20 Motion and Momentum

Section 1 ■ What is motion?Section 2 ■ Acceleration

Directions: Circle the term that correctly completes the sentence.

1. A golfball’s acceleration is +3 m/s2. The ball is (speeding up, slowing down.)

2. An object’s (speed, displacement) represents its distance and direction from its

starting point.

3. A student walks 10 m in 2 s. Her average speed is (20 m/s, 5 m/s).

4. A plane moving at a rate of 400 km/h west has a different (velocity, speed) than a plane moving 400 km/h northwest.

5. During positive acceleration, an object’s final speed is (greater, less) than its initial speed.

6. To calculate acceleration, first subtract the initial speed from the final speed.

Then divide this difference by the (distance moved, time period).

Directions: The graph describes the movement of a car. Match the letters in the graph to the sentences below.

7. The car moves at a constant speed.

8. The car sits motionless at a stoplight.

9. The car undergoes negative acceleration as it approaches a stoplight.

10. The car undergoes positive acceleration as it moves away from a stoplight.

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Content Mastery

Meeting Individual Needs

Velo

city

(km

/hr)

Time (minutes)

10

20

30

40

50

60

70

80

90

10 2 3 4 5 6 7

A

C

D

B

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Directions: Replace each italicized word in the statements below with the correct term.

1. The more velocity an object has the harder it is to slowit down, speed it up, or turn it.

2. Objects with more mass have less inertia.

3. The weight of an object is the amount of matter in anobject.

4. The SI unit for mass is the gram.

5. The tendency of an object to resist change in itsmotion is called speed.

6. The more mass an object has, the harder it is tochange its acceleration.

7. Velocity and momentum are defined the same for allobjects, regardless of their mass.

8. The inertia of an object is a measure of how hard it isto stop an object.

Directions: Answer the following questions on the lines provided.9. State the law of the conservation of momentum.

10. What can the law of conservation of momentum predict?

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Content Mastery

Section 3 ■ Momentum

Name Date Class


Key TermsMotion and Momentum

Directions: Use the clues below to complete the crossword puzzle.

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Content Mastery


1

5

6

4

3

7 8

2

Across

2. A measure of how hard it is to stop an object

4. Distance traveled divided by the time taken to travel the distance

5. Amount of matter in an object

6. Change in velocity divided by the time it takes for the change to occur

7. Speed and direction of motion of an object

Down

1. Speed of an object at one instant of time is the object’s ______ speed

3. Total distance divided by the time taken is an object’s ______ speed

8. Tendency of an object to resist change in its motion

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Directions: Answer the following questions on the lines provided.

1. How do you define motion?

2. When you are in bed asleep, are you in motion? Explain.

3. Explain the difference between distance and displacement.

Directions: In the figure below, you travel from home at A, to the park at B, to the store at C, to a friend’s houseat D. Study the map and answer questions 4 through 8.

What is motion?

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Reinforcement11

4. What distance did you travel?

5. When you were at your friend’s house at D, what was your displacement?6. If you leave home at 1:00 and get to your friend’s house at 5:00, what was your average speed?

7. If you travel from your house at A to the park at B in 0.5 h, what is your velocity?

8. Explain why the speed in question 6 didn’t equal your velocity in question 7.

Directions: Answer the following question on the line provided.9. What does a horizontal line mean on a speed-time graph?


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Acceleration

Directions: In the space provided, substitute a word for the word in italics to make the statement correct.

1. Velocity is a change in an object’s motion.

2. Acceleration is the rate of change of velocity with distance.

3. When an object slows down, it has no acceleration.

Directions: Answer the following questions on the lines provided.4. A merry-go-round horse travels at a constant speed. Is it accelerating? Explain.

5. What is the unit for speed? For acceleration?

6. If an object has an acceleration of –3 m/s2, describe its motion.

Directions: Study the velocity-time graph for an object in motion. Then answer the following questions.

Reinforcement22


Velo

city

Time (s)

5

10

15

20

25

5O 10 15 20 25 30 35 40 45 50

A

C

D

B

E

H

F

G

I

7. In what interval does the object have the fastest acceleration?

8. Over what interval(s) does the object have a negative acceleration?

9. Over what interval is the object stopped?

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Directions: In question 1, below, a code letter has been substituted for every letter of the alphabet. To find outwhat the sentence says, use the following key to decode it. In the key, the code letters are shown directly belowthe letters they stand for. Write the correct letter above each code letter, then read the sentence.

A B C D E F G H I J K L M N O P Q R S T U V W X Y ZL V Y Q G Z M O B P F S R J D T E N I H X C K M A U

1. _______ __________ ______________ ____ _____________ ________H O G H D H L S R D R G J H X R D Z D V P G Y H I H O L H

_____________ ________ ________ __________ _______ _____ __________Y D S S B Q G K B H O G L Y O D H O G N Q D G I J D H Y O L J M G

2. What is the law that is stated above?

Directions: Correctly complete each sentence by underlining the best of the three choices in parentheses.

3. A feather floating in the air has (more, less, the same) momentum as a bowling ball on a shelf.

4. The momentum of an object depends on its mass and (velocity, acceleration, inertia).

5. The tendency for an object to resist change in its motion, is its (momentum, inertia, weight).

6. We say that momentum is conserved, yet objects slow down after collisions. This is because of

(inertia, friction, mass).

Directions: Answer the following questions on the lines provided.7. A 500 g model train car traveling at 0.8 m/s collides with a 300 g stationary car. The cars hook

up and move off down the track together. How fast are they going?

8. Which has a greater momentum, a car or a bike moving at the same speed?

9. What happens when two objects with the same mass collide?

Momentum

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Rolling with a Coaster

Millions of people enjoy roller coasters. Atypical ride on a roller coaster features sharpunexpected turns and a weightless sensationas it descends suddenly. For the engineers thatdesign them, the challenge has been to createsteeper hills, sharper turns, and faster speeds,while ensuring safety for all riders.

Gravity vs. MagnetsThe “traditional” roller coaster would leave

the boarding ramp and usually proceed up alarge steep hill. The plunge down the other sideof the hill provided not only one of the biggestthrills, but also the speed required to propel thecoaster around the track. Many coaster designers now use a series of electromagnets togenerate much greater speeds. With precise timing these magnets first attract and then repelthe cars to increase their speed. Among the advantages of using magnets are less noise fromthe rattle of a chain as it pulls a train to the topof the hill, flexible placement: magnets can beplaced anywhere on the track to increase ordecrease speed, better speed: coasters with magnets are capable of changing speed from 0to 129 km/h in about 2 s, and exceeding 160km/h at some points. Relying only on gravitywill not duplicate this speed performance.

Changes in VelocityEven though speed will always be an essential

part of the coaster experience, some people prefer the sharp turns that appear unexpectedly.In any turn, the speed and the velocity of thevehicle is changed. Advances in engineeringhave allowed the construction of tighter turns.These tighter turns create more friction toreduce the speed as the velocity changes . As acoaster car enters a turn it usually has a greatdeal of velocity. A person in the car has thesame velocity. Both the car’s velocity and theperson’s velocity change suddenly in a turn. Theforces that change the velocity can exceed theforce of gravity, providing the sensation ofbeing smashed into the seat.

Thrill Ride DangersSome coasters generate more force on a

human body than astronauts experience whenthe Space Shuttle blasts off. This can be danger-ous as people may experience reduced visionand even loss of consciousness. Engineers mustavoid designing a thrill ride that exceeds thecapabilities of the human body. With advancesin technology, we could build much faster,sharper turning coasters, but they would createtoo many dangers for the riders.

1. On a traditional, or old-fashioned, roller coaster, how was the speed generated?

2. How do modern coasters generate speed?

3. Describe the changes that occur in the speed and velocity during a sharp curve.

4. The technology exists to make extremely sharp turns at high speeds. Why don’t engineers maketurns as fast and as sharp as they can?

Enrichment11


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Downward Bound

1. What is the term to describe a car increasing in speed?

2. Why does a person riding a bike down a steep hill accelerate faster than on a gradual hill?

3. Explain why a skydiver’s speed won’t continue to increase until his or her parachute opens?

4. Describe two ways a person may increase the free fall speed to greater than 225 km/h.

5. Why must the straps on a parachute be especially strong?

People love fast rides. Whether it is ridingbikes or wagons down a hill, or skiing down asteep slope, we all love the thrill of speed.Regardless of the activity, the one thing thatall these activities rely on is acceleration dueto gravity. The steeper the hill or slope, themore the speed will change as you descend.The most extreme example of gravitationalacceleration is when it is acting to pull a body straight down, like when someone isparachuting.

Rapid AccelerationWhen skydivers jump out of an airplane, they

experience rapid acceleration. After about 12 sof this acceleration, they will reach a velocity ofbetween 160 km/h and 225 km/h. A bicycle ridedown a big hill will reach a top speed with nomore acceleration. The skydiver also reaches atop speed called terminal velocity that is influ-enced by the air resisting the falling body. Theskydiver will continue at this velocity forapproximately 60 s, until the parachute opensand reduces the speed to about 32 km/h.

For most people, falling at 160 km/h isplenty fast, but there are some people who tryto fall faster. Most people change their bodyprofile to reduce wind resistance. This canallow people to travel at more than 483 km/h.

There has been at least one case of a personfalling at over 965 km/h. He jumped at an altitude of over 30,480 m. There were less airparticles to resist a body’s fall at this altitude,and his velocity increased faster than a normaljumper’s.

Training RequiredJust like a person needs to learn how to ride

a bike or to drive a car, a parachutist needs tolearn how to parachute. There are severaltypes of jumps that each require different levels of training. A tandem jump, where youare strapped to the instructor requires theleast amount of training. In contrast, free fall,where the student is accompanied by aninstructor, requires several hours of on theground training. Regardless of what type ofjump, students generally fall for up to 70 sbefore a parachute deploys, or opens.

The rapid change in velocity after the parachute opens can cause strain on the strapsof the parachute. For example a 100 kg personchanging from 193 km/h to 32 km/h in 5 s is an acceleration of –160 km/h or about –44 m/s/s. The straps must be able to withstanda force of 100 kg ✕ –44 m/s2 or –4400 newtons.This force would be about 4.5 times the weightof the parachutist.

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“A Momentous Problem”

Most of us have been outside during a heavyrainstorm. Large drops of water fall hundredsof meters from the sky and strike Earth. Eventhough raindrops form hundreds of meters inthe air and fall to the ground, they don’t injurepeople or damage buildings or other structuresbecause they have very little momentum. Ifheavier objects were to fall from such heights itwould be a very dangerous situation. The combination of large mass and high velocitygives an object a lot of momentum.

Momentum in the Everyday WorldThe concept of momentum has countless

applications in the practical world. One everyday example is automobiles. We all knowthat cars come in many sizes. People drive atdifferent speeds in a variety of conditions. Thesetwo factors contribute to a car’s momentum.The momentum of a vehicle is directly relatedto how quickly it can stop. Small cars, with asingle driver, don’t have as much weight,therefore they have less momentum, and canstop quickly, in a short distance. Large vehiclescarrying a heavy load have greater momentumand require a longer distance to slow down.

Trains have much more momentum thanautomobiles do. Many freight trains weighthousands of tons, if not more. To slow thesetrains requires not meters, but kilometers.This is one reason train accidents occur. Ifthere is an unexpected obstacle on the tracks,by the time the object is seen there is notenough time to stop, even at slow speeds.

Even a large truck has much less momentumthan a small train and requires much lessstopping distance.

Technology and MomentumBecause some people do not know how to

properly adjust their stopping distancedepending on the speed and weight of theirvehicle, new products exist to better estimatestopping distance. On some trains, a computerconstantly evaluates speed, load size, and thetrack ahead to adjust the engine speed accordingly. Similarly, some tractor-trailertrucks are equipped with radar to “look” aheadof the vehicle and reduce speed if objects aretoo close. This radar system has reduced thenumber rear end accidents by over 35%. Thisradar system may also be available for cars inthe near future. These new products may noteliminate accidents completely, but they aredefinitely minimizing human error.

Technology continually provides us withways to overcome “human error.”Understanding how your vehicle behaves andhow long it takes to stop is acquired withexperience. Even with experience though, weare, after all, still human, and sometimes havepoor judgment. The use of computers to calculate stopping distance, based on speed,weight, and momentum, will eliminate somecollisions. Whether you drive a car, heavytruck, or a train, being able to control itsmomentum is part of being a safe driver.

1. Momentum is determined by what two factors?

2. How is momentum of an object related to stopping distance?

3. Explain why computers are used to help vehicles stop.

4. Why is a railroad crossing dangerous for car drivers?

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Section 1 What is motion?

A. All matter is constantly in ________________.

B. Motion involves a ________________ in position.

1. An object changes position relative to a ___________________ point.

2. __________________ is the total length of the route an object travels when it moves.

3. ______________________ includes distance and direction of the stopping point from the

starting point.

C. Distance traveled divided by the time taken to travel the distance is called _______________.

1. The formula for _______________ can be written as: speed = distance/time.

2. The units of speed are units of distance divided by units of time; in SI units, speed is given

as ___________________________ (m/s).

3. An object in motion can change ________________ many times as it moves from one

point to another, speeding up or slowing down.

a. _______________________ is the total distance traveled divided by total time taken.

b. An object’s speed at a particular moment in time is

called _____________________________.

c. __________________ speed occurs when an object travels at a steady rate with the same

instantaneous speed for some period of time.

D. Motion can be _________________ on a distance-time graph with time plotted on the

horizontal axis and distance plotted on the vertical axis.

1. The steeper the line on a distance-time graph, the greater the _______________.

2. A horizontal line on a distance-time graph indicates that no change in

__________________ is occurring, and the speed is ______________.

E. __________________—speed of an object and its direction of motion; velocity changes if

either, or both, of these changes.

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Note-takingWorksheet

Motion and Momentum


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Section 2 Acceleration

A. ______________________—change in velocity divided by the time for the change to occur; itcan include an object’s speeding up, slowing down, and/or changing direction.

B. Acceleration can be ____________________ if you know how an object’s velocity has changedduring a given time period.

1. The formula for calculating ______________________ is: acceleration = final speed – initial speed/time or a = (s f – s i)/t.

a. The unit of acceleration is distance divided by time squared; in SI units, acceleration is

given as ___________________________________ (m/s2).

b. Acceleration is __________________ when an object speeds up and

__________________ when an object slows down.

2. Accelerated motion can be _________________ with speed on the vertical axis and time onthe horizontal axis.

a. An object that is speeding up will have a line on a speed-time graph that

slopes ________________.

b. An object that is slowing down will have a line on a speed-time graph that

slopes __________________.

c. A horizontal line would indicate acceleration of ______________, or constant speed.

Section 3 Momentum

A. The amount of matter in an object is its mass; _________________ is the tendency of anobject to resist a change in its motion.

B. __________________—measure of how hard it is to stop an object; calculated as mass timesvelocity

1. With __________________ expressed as p, the equation can be written as: p = mv.

2. Momentum ____________________if the mass or velocity of the object increases.

3. Momentum has direction that is the same direction as its velocity.M

eeting Individual Needs

Note-taking Worksheet (continued)

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C. __________________________________________ the total momentum of objects that collide with each other does not change.

1. There are ______________ ways collisions can occur.

a. In one type, objects stick together and ______________ still stuck together, althoughpossibly at different speeds.

b. In another type, two objects bounce off each other when they collide, and may transfer______________________ from one to the other.

2. In both cases, the _______________ momentum of the objects that collide is the samebefore and after the collision.

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Note-taking Worksheet (continued)

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Chapter Review

Motion and Momentum

Part A. Vocabulary ReviewDirections: Write the terms that are defined below on the lines provided.1. When objects collide, the total initial momentum equals the total final momentum.

2. the tendency of an object to resist change in its motion

3 the rate of change of velocity

4. the distance traveled divided by the time it takes to travel that specific distance

5. a measure of how hard it is to stop an object

6. speed plus direction

7. the amount of matter in an object

8. speed of an object at one instant of time

Part B. Concept ReviewDirections: Circle the terms that best complete the following statements.

1. The momentum of a falling leaf is (greater than, less than, equal to) the momentum of a fallingpinecone.

2. Two objects each have a mass of 70 kg. Their momentum is (equal, changing, unknown).

3. When two pool balls collide and move away from each other, they eventually stop. This is

because of (momentum, friction, inertia).

4. A 50 kg object moves with a velocity of 10 m/s. Its momentum is (500 m/s2, 5 kg m/s, 500 kg m/s).As

sess

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Chapter Review (continued)


Directions: The distance-time graph below describes the motion of an object. Use it to answer questions 5through 8.

Assessment

Dist

ance

(m)

Time (s)

2

4

6

8

2 4 6 8 10 12 14

A

C D

E

B

5. Over which interval is the velocity greatest?

6. Over which intervals(s) is the velocity zero?

7. Over which interval(s) is the object accelerating?

8. What is the average velocity in m/s from A to B?

Directions: Use the spaces below to calculate the answers to the following questions.9. The velocity of an object goes from 4 m/s to 12 m/s in 4 s. What is its acceleration?

10. A 600 g toy car moving at 3 m/s collides and hooks up with a 900 g toy car at rest and theymove off together. What is their final velocity?

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Chapter Test

Motion and Momentum

I. Testing ConceptsDirections: Use each of the listed terms in a complete sentence.

1. speed

2. average speed

3. velocity

4. acceleration

5. negative acceleration

6. mass

7. inertia

8. momentum

9. displacement

10. law of conservation of momentum

II. Understanding ConceptsDirections: Match the units in the right-hand column with the terms in the left-hand column.

1. distance

2. speed

3. acceleration

4. momentum

5. mass

Asse

ssm

ent

a. kg m/s

b. m/s2

c. kg

d. m/s

e. m

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Chapter Test (continued)


Skill: Interpreting Graphs

Directions: Use the graph of a girl riding her bike to the store and back to answer the following questions.

Assessment

Dist

ance

(km

)

Time (min)

1

2

3

4

10 20 30 40 50 60 70 80 90 100 110

A

C

D

E

B

6. Over what interval is the velocity the greatest?

7. Over what interval(s) is the velocity zero?

8. Where might the girl have stopped for at traffic light?

9. What is the girl’s velocity in km/h between A and B?

Directions: On the lines at left, write the letter of the term that best completes the statement.

10. Two km south is a measure of ______.a. distance b. displacement c. velocity d. acceleration

11. A 10-kg object has a momentum of 50 kg m/s. Its velocity is ______.a. 10 m/s b. 5 m/s2 c. 5 m/s d. 500 m/s

12. An object’s inertia depends on its ______.a. mass b. weight c. momentum d. gravity

13. Momentum depends on ______ and ______.a. mass, weight c. velocity, weightb. weight, inertia d. mass, velocity

14. The hands of a clock ______.a. have a constant velocity c. constantly change speedb. have no momentum d. are accelerating

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III. Applying ConceptsDirections: Study the graphs below and answer questions 1 through 4.

Asse

ssm

ent1. In which graph(s) is the velocity constant?

2. In which graph(s) is the velocity zero?

3. In which graph(s) does the object have a positive acceleration?

4. In which graph(s) does the object have a negative acceleration?

Directions: Answer the following questions on the lines provided.5. Describe the motion of a car with acceleration of –5 m/s2.

6. If an object moves at constant speed, can we assume that is not accelerating? Explain.

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Name Date Class



Assessment

7. A car travels 10 km north, 5 km east, 15 km south, then 5 km north.

a. What is the distance it travels?

b. What is its displacement?

8. An object’s velocity changes from 30 m/s to 23 m/s in 3 s. What is its acceleration?

9. A 5-kg object moving at 20 m/s collides with a 10-kg object moving a 5 m/s. They stick

together and move off together. What is their final velocity?

IV. Writing SkillsDirections: Answer the following questions using complete sentences.1. You flew in an airplane from Denver to San Francisco, and your friend rode in a car for the

same trip. For which one of you would the displacement most nearly equal the distance?Explain.

2. You hear on a weather report that a tornado in a town near you is moving at 25 km/h. Is thisenough information to know whether or not you are in danger? Explain.

3. What is momentum and how does it differ from inertia?

4. A tennis ball and a bowling ball have the same velocity. Which would be harder to stop?

Explain.

5. How do you explain conservation of momentum when a rocket ship takes off?


What is motion?Study Guide11Directions: Fill in the chart using information from the chapter.

Directions: List three ways the velocity of a car can change.

6.

7.

8.

Directions: Explain how the speed of an object is changing if the line representing the object’s motion on adistance-time graph becomes steeper.

9.

Directions: Explain how the displacement of an object could be zero while the distance the object travels is 150 m.

10.

Name Date Class

Term Definition Includes Direction?

1. distance

2. displacement

3. average speed

4. instantaneous speed

5. velocity

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10Chapter

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Name Date Class


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Acceleration

Directions: In the space provided, substitute a word for the word in italics to make the statement correct.

1. Velocity is a change in an object’s motion.

2. Acceleration is the rate of change of velocity with distance.

3. When an object slows down, it has no acceleration.

Directions: Answer the following questions on the lines provided.4. A merry-go-round horse travels at a constant speed. Is it accelerating? Explain.

5. What is the unit for speed? For acceleration?

6. If an object has an acceleration of –3 m/s2, describe its motion.

Directions: Study the velocity-time graph for an object in motion. Then answer the following questions.

Study Guide22Ve

loci

ty

Time (s)

5

10

15

20

25

5O 10 15 20 25 30 35 40 45 50

A

C

D

B

E

H

F

G

I

7. In what interval does the object have the fastest acceleration?

8. Over what interval(s) does the object have a negative acceleration?

9. Over what interval is the object stopped?

10Chapter


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Directions: In question 1, below, a code letter has been substituted for every letter of the alphabet. To find outwhat the sentence says, use the following key to decode it. In the key, the code letters are shown directly belowthe letters they stand for. Write the correct letter above each code letter, then read the sentence.

A B C D E F G H I J K L M N O P Q R S T U V W X Y ZL V Y Q G Z M O B P F S R J D T E N I H X C K M A U

1. _______ __________ ______________ ____ _____________ ________H O G H D H L S R D R G J H X R D Z D V P G Y H I H O L H

_____________ ________ ________ __________ _______ _____ __________Y D S S B Q G K B H O G L Y O D H O G N Q D G I J D H Y O L J M G

2. What is the law that is stated above?

Directions: Correctly complete each sentence by underlining the best of the three choices in parentheses.

3. A feather floating in the air has (more, less, the same) momentum as a bowling ball on a shelf.

4. The momentum of an object depends on its mass and (velocity, acceleration, inertia).

5. The tendency for an object to resist change in its motion, is its (momentum, inertia, weight).

6. We say that momentum is conserved, yet objects slow down after collisions. This is because of

(inertia, friction, mass).

Directions: Answer the following questions on the lines provided.7. A 500 g model train car traveling at 0.8 m/s collides with a 300 g stationary car. The cars hook

up and move off down the track together. How fast are they going?

8. Which has a greater momentum, a car or a bike moving at the same speed?

9. What happens when two objects with the same mass collide?

MomentumStudy Guide33 10Chapter


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Construct the Foldable as directed at the beginning of this chapter.

Motion and MomentumBefore You ReadPreview the chapter and section titles and the section headings. Complete thetwo columns of the table by listing at least two ideas in each column.

Name Date


Describe how your motion changed as you moved from your school’s entrance to your classroom.

Science Journal

K WWhat I know What I want to find out

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NewVocabulary

ReviewVocabulary

AcademicVocabulary

Name Date

Motion and MomentumSection 1 What is motion?


meter

speed

average speed

instantaneous speed

velocity

displace

Preview the section by reading the What You’ll Learn statements.Write three questions that come to mind from reading thesestatements.

1.

2.

3.

Write a sentence that uses the word meter to show its scientificmeaning.

Define the new vocabulary terms using your book or adictionary.

Use a dictionary to define displace in its scientific sense.

Analyze the meaning of relative motion. Complete the sentences.

To determine whether something changes position, you must

identify . An object changes position if

.

Contrast distance and displacement. Draw a diagram showingdistance and displacement for a person jogging halfway around alake. Label the distance and displacement.

Complete the equation for calculating speed.

speed (in meters/second) =

Compare and contrast average speed and instantaneousspeed. Give an example of average speed, instantaneous speed,and one in which instantaneous speed changes.

Average speed:

Instantaneous speed:

Example:

Section 1 What is motion? (continued)

ChangingPosition

I found this informationon page .

SpeedI found this information

on page .

Name Date


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Analyze the distance-time graph. Graph lines to show:

• Person C, whose speed is 2 m/s.

• Person D, who is standing still.

Compare the speed of each person by completing the paragraph.

is plotted on the horizontal axis and

is plotted on the vertical axis. A steeper

line indicates . On this graph, Person A

has a speed of and Person B has a speed

of . If speed were zero, the line would

be .

Section 1 What is motion? (continued)

Graphing MotionI found this information

on page .

Name Date


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Distance v. Time

Person A

Person B

0 0.5 1.0 1.5 2.0 2.5 3.0Time

2.0

1.5

1.0

0.5

0

Dis

tan

ce

Think of a time recently when you might have run around a trackor traveled in a car or bus. Describe the motion thoroughly. Remember to include howyour velocity changed.

CONNECT IT

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ReviewVocabulary

AcademicVocabulary

Name Date

Motion and MomentumSection 2 Acceleration

NewVocabulary


kilogram

acceleration

positive

Predict three things you will learn in this section. Read the sectiontitle and subheadings to help you make your predictions.

1.

2.

3.

Define kilogram.

Use your book to write the scientific definition of acceleration.

Use a dictionary to find the mathematical definition of positive.

Distinguish the three ways that an object can accelerate. Completethe concept map.

Complete the mathematical equation to calculate acceleration forobjects moving in a straight line.

Acceleration Equation

acceleration �(in m/s) � (in m/s)

(in m/s2) time (in s)

Analyze the equation above to rewrite it using symbols.

a �

Compare and contrast positive and negative acceleration bycompleting the chart.

Section 2 Acceleration (continued)

Acceleration and Motion


CalculatingAcceleration



Name Date


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Types of Acceleration

Positive Negative

Change inspeed

Relationship of Initial speed is initial speed to less than final final speed speed.

Acceleration

includes

2.1. 3.

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Analyze the acceleration graph below. Label the parts of the graphshowing zero acceleration, positive acceleration, and negativeacceleration.

Summarize how you can identify each type of acceleration on anacceleration graph. Complete the sentences.

A line for positive acceleration slopes .

A line for negative acceleration slopes .

A line for zero acceleration .

Section 2 Acceleration (continued)

CalculatingAcceleration


Name Date


A jogger runs around a circular track. She starts at a speed of 2 m/s, then speeds up to 6 m/s. She runs at that speed for 20 minutes, and thencomes to a stop. Describe her acceleration. Is it ever zero?

SYNTHESIZE IT

Speed v. Time

1 2 3 4 5 6 7 8 9Time (s)

8

7

6

5

4

3

2

1

0

Spee

d (

m/s

)

triple-beam balance

mass

inertia

momentum

law of conservation of momentum

predict

Scan the headings, bold words, and illustrations in Section 3.Write two facts you discovered about momentum as you scannedthe section.

1.

2.

Use the term triple-beam balance in a sentence.

Define the scientific meanings of the new vocabulary terms usingyour book or a dictionary.

Use a dictionary to define predict.

NewVocabulary

ReviewVocabulary

AcademicVocabulary

Name Date

Motion and MomentumSection 3 Momentum


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Label the arrow below to show the relationship between mass and inertia.

List two factors that affect an object’s momentum.

Summarize the calculation of momentum in words on the lines below.

Complete the equation used to calculate momentum.

momentum � (in kg) � (in m/s)(in kg • m/s)

Analyze the equation above and rewrite it using symbols. Use theletter p to represent momentum.

Summarize the law of conservation of momentum in your ownwords. Two balls that collide are an example.

momentum1.

affect

2.

Section 3 Momentum (continued)

Mass and InertiaI found this information

on page .

MomentumI found this information

on page .

Conservation of Momentum


Name Date


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Has inertia

Has inertia

Greatermass

Lessmass

Model the law of conservation of momentum when a moving objectof small mass collides with an object of greater mass that is initiallyat rest. In the first row, model what happens if the two objects sticktogether. In the second, model what happens if the two bounceaway from each other.

• Use arrows to show the size and direction of each object’smomentum.

• Label each object with its mass, speed, and direction.

Section 3 Momentum (continued)

Using MomentumConservation


Name Date


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Before Impact After Impact

Bou

nce

off

Stic

k to

geth

er

At a science fair, contestants can win a prize if they can roll a ballwith a specific momentum chosen by the presenter. The contestants have a choice oftwo balls. One has greater mass than the other. Which would you choose, and why?

CONNECT IT

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Tie It TogetherName Date


Work with a partner to perform the experiment below to explore changes in momentum.

Materials

wooden block stopwatch

ball that will roll easily tape

meterstick triple-beam balance

1. Find and record the mass of the block and ball, using the balance.

Block:

Ball:

2. Mark a line on the floor with tape. Place the block on the line. Measure a distance of5 m from the line and mark a second line.

3. Practice rolling the ball until you can roll it from the 5-m line to the block.

4. Roll the ball from the 5-m line to the block. Use the stopwatch to time the roll.Then measure how far the block moved from the line when the ball hit it. Use a chart like the one below to record your data.

5. Repeat step 4 four more times, varying the speed with which you roll the ball. Recordthe time and distance for each trial.

6. Use your data to calculate the speed for each trial. Then use that information and themass of the ball to calculate the momentum of the ball in each trial.

7. Analyze your data. What relationship do you see between the momentum of the balland the distance the block moved? Why do you think this relationship exists?

Trial Time Speed Momentum Distance Block Moved

1

2

3

4

5

Data Table

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Motion and Momentum Chapter Wrap-Up

Review the ideas you listed in the chart at the beginning of the chapter. Cross out anyincorrect information in the first column. Then complete the chart by filling in the third column.

Name Date

After reading this chapter, identify three things that you havelearned about motion and momentum.

SUMMARIZE IT

ReviewUse this checklist to help you study.

Review the information you included in your Foldable.

Study your Science Notebook on this chapter.

Study the definitions of vocabulary words.

Review daily homework assignments.

Re-read the chapter and review the charts, graphs, and illustrations.

Review the Self Check at the end of each section.

Look over the Chapter Review at the end of the chapter.


K W LWhat I know What I want to find out What I learned

1. Explain What do youcompare an object towhen determining theobject’s motion?

Underline As you read,underline material you do notunderstand the first time youread it. Reread the informationuntil you understand it. Ask yourteacher if you still do notunderstand it after rereading it.

Motion and Momentum

section ● What is motion?1

What You’ll Learn■ what distance, speed,

and velocity are■ how to graph motion

Read to Learn

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Before You ReadWhen you move from place to place, how do you know youhave moved? Write what you think on the lines below.

Matter and MotionWhen you are sitting quietly in a chair, are you in

motion? It may surprise you to know that all matter in theuniverse is always in motion. Think about it. In the chair,your heart beats and you breathe. Your blood circulatesthrough your veins. Electrons move around the nuclei ofevery atom in your body.

Changing PositionHow do you know if something is in motion? Something

is in motion if it is changing position. Changing positionmeans moving from one place to another. Imagine runnersin a 100-meter race. They sprint from the start line to thefinish line. Their positions change, so they are in motion.

What is relative motion?To find out if something changes position, you need a

reference point to compare it to. An object changes positionif it moves when compared to a reference point. Imagineyou are competing in the 100-meter race. You begin justbehind the start line. When you pass the finish line, you are100 m from the start line. If you use the start line as yourreference point, then your position has changed by 100 mwhen compared to the start line. You were in motion.

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Reading Essentials 153

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Picture This2. Explain Why is the

displacement in the thirdfigure zero?

●A Organize InformationMake the following two-tabFoldable to help you organizeinformation about how todescribe and calculate speed.Write examples under the tabs.

Speed �Distance

Time

SI units m/s

What are distance and displacement?Suppose you walk from your house to the park around

the block. How far away is it? That depends on whether youare talking about distance or displacement. Distance is thelength of the route you travel.

Suppose you travel 200 m from your house to the park.How would you describe your location now? You could sayyou are 200 m from your house. But where you are dependson both the distance you travel and direction. To describeexactly where you are, you need to tell the direction fromyour house. Displacement includes the distance betweenyour starting and ending points and the direction in whichyou travel. The figure above shows the difference betweendistance and displacement.

SpeedWhen you describe motion, you usually want to say how

fast something is moving. The faster something is moving,the less time it takes to travel a certain distance. The slowersomething is moving, the more time it takes to travel acertain distance. Speed is the distance traveled divided bythe time it takes to travel that distance. Speed can becalculated with this equation:

speed (in meters/second) �distance (in meters)

time (in seconds)

s �dt

In SI units, distance is measured in m and time is measuredin s. The SI measurement for speed is meters per second(m/s). This is the SI distance unit divided by the SI time unit.

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Distance: 40 mDisplacement: 40 m east

Distance: 70 mDisplacement: 50 m northeast

Distance: 140 mDisplacement: 0 m

40 m

50 m 30 m

N N N


3. Identify What type ofspeed does the speedometerin a car show?

Picture This4. Calculate What is the

average speed of both ballsin the diagram? Show allyour work.

What is average speed?Suppose a sprinter ran the 100-m dash in 10 s. Did she

run the whole race at a speed of 10 m/s? No, her speedcould have been different at any instant during the race. Youcan describe her motion for the entire race by her averagespeed, 10 m/s. Average speed is the total distance traveleddivided by the total time taken to travel the distance.

What is instantaneous speed?Have you ever watched the speedometer when you are

riding in a car? If the speedometer reads 50 km/h, the car istraveling at 50 km/h at that instant. Instantaneous speed isthe speed of an object at one instant of time.

How do average and instantaneousspeed differ?

If it takes two hours to travel 200 km in a car, the averagespeed would be 100 km/h. But the car probably was notmoving at this speed the whole time. It might have gonefaster on the freeway and stopped at stoplights. There yourspeed was 0 km/h. If the car were able to travel 100 km/hthe whole time, you would have moved at a constant speed.

For another example, see the diagram of the two ballsbelow. Both balls have the same average speed because theyboth travel 3 m in 4 s. The top ball is moving at a constantspeed. In each second, it moves the same distance. Thebottom ball is moving at different speeds. Its instantaneousspeed is fast between 0 s and 1 s, slower between 2 s and3 s, and even slower between 3 s and 4 s.

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0 s 1 s 2 s 3 s 4 s

0 m 1 m 2 m 3 m

0 s 1 s 2 s 3 s 4 s

0 m 1 m 2 m 3 m


5. Calculate Look at thegraph. How much fartherhas student A walked in 2seconds than student B?

6. Explain When the car’smotion changed from 40km/h north to 40 km/h east,what changed?

Applying Math

Graphing MotionYou can show the motion of an object with a distance-time

graph. In a distance-time graph, time is plotted on thehorizontal axis. Distance is plotted on the vertical axis.

How do distance-time graphs compare speed?The graph below is a distance-time graph that shows the

motion of two students walking. According to the graph,after 1 s student A traveled 1 m. Her average speed is 1 m/1 s,or 1 m/s. Student B traveled only 0.5 m in 1 s. His averagespeed is 0.5 m/1 s, or 0.5 m/s. So student A traveled fasterthan student B. Now compare the steepness of the lines inthe graph. The line for student A is steeper than the line forstudent B. A steeper line shows a faster speed. If the line ishorizontal, no change in position happens. A horizontal linemeans a speed of zero.

VelocitySuppose you are hiking in the woods. You may want to

know how fast you are hiking. But you also need to know thedirection you are going or you might get lost. The velocityof an object is the speed of the object and the direction ofits motion. Velocity has the same units as speed andincludes the direction of motion, for example 20 km/h east.

Velocity can change when speed changes, directionchanges, or both change. If a car that is moving 60 km/hslows to 40 km/h, its velocity has changed. Suppose a car istraveling 40 km/h north. It then goes around a curve until itis heading east. All the time, the car’s speed was 40 km/h.But the velocity changed. The velocity was 40 km/h north.Now it is 40 km/h east.

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Distance v. Time

2.0

1.0

1.0 1.50.50Time (s)

2.0 2.5

Dis

tanc

e (m

)

0

0.5

1.5Student A

Student B


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1. Review the terms and their definitions in the Mini Glossary. Ramona divided thedistance from her house to school by the time it took her to walk that distance. Whatquantity did Ramona find? Explain your answer in a complete sentence.

2. The distance-time graph below is for a bicyclist in a bicycle race.

a. What was the bicyclist’s average speed aftertwo hours?

b. What happened to her speed during the race?

c. How can you tell?

d. What was her average speed for the entire race?

After You ReadMini Glossaryaverage speed: equals the total distance traveled divided

by the total time taken to travel the distanceinstantaneous speed: the speed of an object at one instant

of time

speed: equals the distance traveled divided by the time ittakes to travel that distance

velocity: the speed of an object and the direction ofits motion

End ofSection

Visit ips.msscience.com to access your textbook, interactivegames, and projects to help you learn more about motion.


160

140

120

100

80

60

40

20

01 2 3 4 5 6

Dis

tanc

e (k

m)

Time (hours)


Outline Create an outline ofthis section as you read. Be sureto include main ideas,vocabulary terms, and otherimportant information.

●B Classify Make thefollowing three-tab Foldable tohelp you classify and understandthe different types ofacceleration.

Study Coach

Motion and Momentum

section ● Acceleration2

What You’ll Learn■ what acceleration is■ to predict how

acceleration affectsmotion

Read to Learn

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Before You ReadHave you ever been in a foot race? What kinds of things aremeasured in a foot race?

Acceleration and MotionHave you ever seen a rocket launch? When the rocket first

lifts off, it seems to move very slowly. But very soon therocket is moving at a fast speed. How can you describe thechange in the rocket’s motion? When an object changes itsmotion, it is accelerating. Acceleration is the change invelocity divided by the time it takes for the change to happen.

How is speeding up acceleration?When you first get on a bike, it is not moving. When you

start pedaling, the bike moves faster and faster. This isacceleration. An object that is already moving can acceleratetoo. Imagine you are biking along a level path. When youstart to pedal harder, your speed increases. When the speedof an object increases, the object is accelerating.

How is slowing down acceleration?Suppose you are biking at a speed of 4 m/s. If you brake,

you will slow down. It might sound odd, but when you slowdown you are accelerating. Any change in velocity isacceleration. Acceleration happens when an object speedsup or slows down.

When an object is speeding up, its acceleration is in thesame direction as its motion. When an object is slowing down,its acceleration is in the opposite direction of its motion.

chapter

310


Acceleration:Object

Speeds Up

Acceleration:Object

Slows Down

Acceleration:Object Turns,

ChangesDirection


1. Explain how an objectaccelerates when itchanges direction.

2. Calculate A sports caraccelerates from zero to 28m/s in 4 seconds. What is itsacceleration?

Applying Math

How is changing direction acceleration?Remember that acceleration is a change in velocity. A

change in velocity can be a change in speed, direction, or both.So, when an object changes direction, it accelerates. Think ofyourself on a bicycle. If you lean to one side and turn thehandlebars that direction, you turn. The direction of the bike’smotion changes, so the bike accelerates. The acceleration is inthe direction the bike turns.

Imagine throwing a ball straight up into the air. The ballstarts out moving upward. After a while the ball stopsmoving upward and begins to come back down. The ballhas changed its direction of motion. The ball is nowaccelerating downward.

Calculating AccelerationIf an object is moving in a straight line, its acceleration

can be calculated with this equation.

acceleration (m/s2) � final speed (m/s) � initial speed (m/s)

time (seconds)

a �(sf – si)

t

In this equation, time is the length of time it takes for themotion to change. Initial speed is the starting speed.Acceleration has units of meters per second squared (m/s2).

What are positive and negative acceleration?Suppose you are riding your bike in a straight line. You

speed up from 2 m/s to 8 m/s in 6 seconds.

a � (sf – si)

t

�(8 m/s � 2 m/s)

�6 m/s

� �1 m/s2

6s 6s

So your acceleration is �1 m/s2. Now suppose you slowdown from 8 m/s to 2 m/s in 6 s.

a � (sf – si)

t

�(2 m/s � 8 m/s)

��6 m/s

� �1 m/s2

6s 6s

Your acceleration is �1 m/s2.

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Picture This4. Interpret Data For

how many seconds doesthe object in the speed-time graph have anacceleration of zero?

3. Identify What type ofacceleration do you have ifyou are slowing down?

What does negative acceleration mean?When you speed up, your acceleration is positive. When

you slow down, your acceleration is negative. That isbecause when you slow down, your final speed is less thanyour initial speed. This gives you a negative value in theequation and a negative acceleration.

How do you graph accelerated motion?You can show the motion of an accelerating object on a

graph. For this type of graph, speed is plotted on thevertical axis. Time is plotted on the horizontal axis. Thegraph below is an example.

Positive Acceleration In section A of the graph, speedincreases from 0 m/s to 10 m/s during the first 2 seconds.Acceleration is 5 m/s2. An object that is speeding up willhave a line that slopes up on a speed-time graph.

Zero Acceleration In section B of the graph, the speeddoes not change. If speed does not change, the object is notaccelerating. A horizontal line on a speed-time graph meanszero acceleration.

Negative Acceleration In section C of the graph, theobject goes from 10 m/s to 4 m/s in 2 s. Acceleration is�3 m/s2. You can see that the line on the graph slopesdownward as an object slows down.

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Speed v. Time

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1 2 3 4 5 6Time (s)

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1. Review the term and its definition in the Mini Glossary. Describe the term acceleration inyour own words.

2. Fill in the chart with the different ways an object can accelerate.

3. Why do you think that slowing down is sometimes called deceleration instead of acceleration?

After You ReadMini Glossaryacceleration: the change in velocity divided by the time it

takes for the change to happen; occurs when an objectspeeds up, slows down, or turns

End ofSection

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Acceleration


Identify the Main PointWhen you read each paragraph,look for the main point or mainidea. Highlight it or write itdown. When you finish reading,make sure you understand eachmain point.

1. Determine Which hasmore inertia, a soccer ball ora bowling ball?

Study Coach

Motion and Momentum

section ● Momentum3

What You’ll Learn■ how mass and inertia

are related■ what momentum is■ to use the law of

conservation ofmomentum topredict motion

Read to Learn

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Before You ReadWhat happens if you are riding in a car and the driverslams on the brakes? Explain on the lines below.

Mass and InertiaOne important property of objects is mass. The mass of

an object is the amount of matter in the object. The SI unitfor mass is the kilogram. Mass is related to weight. Objectswith more mass weigh more than objects with less mass. Abowling ball has more mass than a pillow. So, it weighsmore. But a pillow is larger. The size of an object is not thesame as its mass.

Think about what happens when you try to stop someonewho is running toward you. It is easier to stop a small childthan an adult. The more mass an object has, the harder it isto start moving, stop moving, slow down, speed up, or turn.Inertia is the tendency of an object to resist a change in itsmotion. The more inertia an object has, the harder it is tochange its motion.

MomentumYou know that the faster a bicycle moves, the harder it is

to stop. The momentum of an object is the measure of howhard it is to stop the object. It depends on the object’s massand velocity. Momentum is usually symbolized by p.

momentum (in kg • m/s) � mass (in kg) � velocity (in m/s)p � mv

chapter

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2. Use FormulasCalculate the momentum ofa 14-kg bicycle travelingnorth at 2 m/s. Show allyour work.

3. Identify The law ofconservation of momentumaffects objects that

a. rotate.b. turn.c. collide.d. roll.

●C Organize InformationMake the following Foldable tohelp you organize informationabout how momentum istransferred and the law ofconservation of momentum.

Applying MathMass is measured in kilograms. Velocity is measured inmeters per second. So, the unit of momentum is kilogramsmultiplied by meters per second (kg • m/s). Momentum hasa direction that is the same as the direction of the velocity.

Conservation of MomentumWhen you play billiards, you knock the cue ball into

other balls. When a cue ball hits another ball, the motion ofboth balls changes. The cue ball slows down and maychange direction. So its momentum decreases. The otherball starts moving. So its momentum increases.

What happens to lost momentum? The momentum lost by the cue ball is moved to the other

ball. It is gained by the other ball. This means that the totalmomentum of the two balls was the same just before and justafter the collision. This is true for any collision, but only aslong as no outside forces like friction act on the objects. Thelaw of conservation of momentum states that the totalmomentum of objects that collide is the same before and afterthe collision. This is true for the collision of the billiard balls.It is also true for collisions of atoms, cars, football players, orany other matter.

Using Momentum ConservationOutside forces are almost always acting on objects that

are colliding. These are forces like friction and gravity. Butsometimes, these forces are very small and can be ignored.Then the law of conservation of mass can be used to predicthow the motions of objects will change after a collision.

What happens after objects collide?There are many ways that collisions can happen.

Sometimes the objects that collide will bounce off eachother. In another type of collision, objects stick to eachother after they collide.

Bounce Off What happens when you knock down bowlingpins with a bowling ball? Picture a bowling ball rolling downthe alley and hitting some bowling pins. The bowling balland pins bounce off each other. When the ball hits the pins,some of the ball’s momentum is transferred to the pins. Theball slows down and the pins speed up. The speeds change,but the total momentum does not. Momentum is conserved.

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Transferof

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Law ofConservation

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4. Predict Will the velocityof the student and thebackpack together be fasteror slower than the velocityof the backpack by itself?

5. Calculate Find thevelocity of the student andthe backpack if thebackpack’s mass is 3 kg, itwas tossed at a velocity of4 m/s, and the mass of thestudent is 57 kg. Show allyour work.

Applying Math

Stick together Suppose you’re watching a football gamewhen one player tackles another. The two players collide,but instead of bouncing apart, they stick together. Thespeeds of both players change, but the total momentumdoes not. In this type of collision, momentum also isconserved. In both of these types of collisions, you can usethe law of conservation of momentum to find the speeds ofthe objects after they collide.

How do you calculate the momentum oftwo objects that stick together?

Imagine you are standing still on a pair of skates. You arenot moving. Then someone standing in front of you throwsyou a backpack. You catch the backpack and begin to movebackwards. You and the backpack move in the samedirection that the backpack was moving before the collision.

You can use the law of conservation of momentum tofind your velocity after you catch the backpack. Suppose thebackpack has a mass of 2 kg and is tossed at a velocity of 5 m/s.Your mass is 48 kg and you have no velocity because you arestanding still. So, your velocity before the collision is 0 m/s.

First, find the total momentum of you and the backpack.Remember, momentum equals mass times velocity.

total momentum � your momentum � backpack momentum� (48 kg � 0 m/s) � (2 kg � 5 m/s)� 0 kg • m/s � 10 kg • m/s� 10 kg • m/s

The law of conservation of momentum tells you that thetotal momentum before the collision is the same as the totalmomentum after the collision. After the collision, the totalmomentum does not change. You and the backpack havebecome one object and are moving at the same velocity. Youcan use the equation for momentum to find the final velocity.

total momentum � (mass of backpack � your mass) � velocity10 kg • m/s � (2 kg � 48 kg) � velocity10 kg • m/s � (50 kg) � velocity10 kg • m/s

� velocity(50 kg)

0.2 m/s � velocity

Your velocity right after you catch the backpack is 0.2 m/s.

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Picture This6. Describe From which

marble to which marblewas momentum moved?

7. Analyze Would the totalmomentum still be zero ifone marble had greatermass than the other marble?

Applying Math

Stopping Friction between your skates and the ground willslow you down as you move on your skates. The momentumof you and the backpack will continue to decrease until youstop because of friction.

How can mass predict motion after collisions?You can use the law of conservation of momentum to

predict collisions between two objects. What happens whenone marble hits another marble that is at rest? It dependson the masses of the marbles that collide. The figure showsa marble with a smaller mass hitting a marble with a largermass. The larger marble is at rest. After the collision, themarble with a smaller mass bounces off in the oppositedirection. The larger marble moves in the same directionthat the small marble was moving.

What if the larger marble hits a smaller marble that is notmoving? Both marbles will move in the same direction. Butthe marble with the smaller mass always moves faster thanthe marble with the greater mass.

How does bouncing affect momentum?Two objects can also bounce off of each other. The two

marbles in the figure have the same mass and are moving atthe same speed. They bounce off each other when theycollide. Before the collision, the momentum of each marblewas the same but in opposite directions. So the totalmomentum was zero. That means that the total momentumafter the collision has to be zero too. The two marbles mustmove in opposite directions with the same speed after thecollision. Then the total momentum is zero again.

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1. Review the terms and their definitions in the Mini Glossary. Explain in completesentences what affects the inertia of an object.

2. The sketch below shows two marbles. The arrows show the size and the direction of themomentum of the two marbles. Draw arrows in the space below that show what willhappen to these two marbles because of the law of conservation of momentum whenthey collide.

3. How can a football game be used to explain inertia and momentum?

After You ReadMini Glossaryinertia: tendency of an object to resist a change in motion.law of conservation of momentum: states that the total

momentum of objects that collide is the same beforeand after the collision

mass: amount of matter in an objectmomentum: the measure of how hard it is to stop an object

End ofSection

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