Focus on California 8th Grade Physical Science Textbook Chapter 10 Forces

Chapter Forces ( Preview ' fortes ( In velocity . As I basis Io ! this a . Student know i fume has both daemon and magnitude Students Is to two or more at one , he result the of all the taxes . students know when the ( ones on an omen are , the molten of the object does not change students know how to the two or more that are on a single object , fours due to lemon ' matter , and . know that when the lanes on an omen aw , the abject change velocity ( that , It speed up , slaw , or change direction ) Students know the greater the mass Di an , mom lone needed to achieve the same rate 01 manna moment as made by asking questions and cow menu . As a basis for this concept and ' um comm ! own and perform . Students wall ( between and ! graphs data and demon ments about between A lane on the

' Form on the BIG Ide What causes an object velocity to change ?

Check What You Know You drop a tennis ball and a baseball at the same time . Why do the balls fall to the floor ?

Chapter 369 Vocabulary The images shown here represent some of the key in this chapter . You can use this vocabulary skill to help you understand the meaning of some key in this chapter . Latin Word Origins Many science words come to from Latin . in this chapter you will learn the word compress Compress tomes from the Latin words ( om meaning together and meaning to Compress means to press together . OM together press to press together Learn these Latin words to help you remember the key terms . Latin Origin I Meaning I Key Term Center centripetal ior ( Projectile Forward , before Projectile Apply It ! Look at and and predict the meaning of projectile . Revise your as needed as you read the chapter . Look for words with these origins as you read the chapter .

, cen petal fo ITS Chapter 10 Vocabulary Section ?

COKE unbalanced form form Section I owe 350 human mu friction rolling friction fluid gravity mass weigh ! her fall on resistance ( tension Section ( 139 meme Section i Ul momentum law ol conservation oi momentum Section mar satellite farce him 101 Build Vocabulary On Ime Visit ( om Web ( ode chapter 10 311

Take Note Science chapters are packed information Each section needs to be read at least twice . After the main idea and important details in a section , take notes so you have something to study . In your notebook , create a organizer . Label the left side Recall Clues and Questions label the right side Notes . Under . write key ideas , using phrases and abbreviations include a few important details . Under Recall Clues and Questions , write review and study questions . Write a summary statement for each red heading . Look at the following example for Section I in this , Recall Clues Questions Whit in force ! What are the SI units for forte ! Apply It ! What are two important ideas found in the notes ! What questions in the left column help you recall the content ?

Notes push or pull I A vector quantity I magnitude and direction I show direction and of force unit called newton ( A ( one Is described Fy i ?

ing ?

rU by the direction in which It ecu . Take notes as you read each section in this chapter Standards Investigation . Newton Scooters Have you ever wondered what force pushes a rocket upward ?

As you will learn in this chapter , an object will accelerate only when a net force acts on it . The rocket accelerates upward because it is acted on by a net force from the gases it pushes outward . This is an example of Newton third law . In this investigation , you will use Newton third law to design a vehicle . Your Goal To design and build a vehicle that moves without me use of gravity . electricity . or a person pushing or pulling it . Your vehicle must move forward by pushing back on something travel a minimum distance of meters be built following the safety guidelines in Appendix A Plan It ! Preview the chapter to find out about third law of motion . Determine factors that will affect the acceleration of your vehicle . Brainstorm possible designs for your vehicle , but be careful not to lock yourself into a single idea . Remember that a car with wheels is only one type of vehicle . Think of ways to use household materials to build your vehicle . Draw a diagram of your proposed design and identify the force that will propel your vehicle . Have your teacher approve your design . Then build your vehicle and see it it works ! Chapter 10 313

90 Standards Focus ( Al Students know a force has both and magnitude Students know when the on an are , the motion ol the object does not ( hange . How is a force described ?

How do balanced and unbalanced affect an ?

Key I force I newton net I unbalanced lanes I balanced forces 37 The Nature of Force , Standards Is the Force With You ?

Attach a spring scale to each end ofa skateboard Plate the skateboard upright . Gently pull on one spring scale with a lone of , while your partner pulls on the other with the same force . Observe the motion of the skateboard . Now try to keep your partner spring scale reading at while you pull with a force of Observe the motion of the skateboard . Think It Over Observing Describe the motion of the skateboard when you and your partner pulled with the same force . How was the motion of the skateboard affected when you pulled with more forte than your partner ?

A hard ( ball shunting the toward the goal . in , goalie . stops the hall , and quickly kicks it in opposite . In a soccer game , the ball is rarely still . Its motion is constantly . causes an object to start moving . stop moving . or change ?

is three . What Is a Force ?

In . the word has ( simple and specific . A force is a push or a pull . You use a force to open a door . to at rubber band . and to carry your backpack . When one object pushes or pulls ' object . you say that the object exerts force on the second object . Like velocity and , force is a vector quantity . A force is described by its magnitude and by the direction in which it acts . If you push on at , you exert a ?

in a than ii you pull on the door .

You can use an arrow to represent the direction and forte . paints in the . The length it ! the ' I ( you the ( Iii a longer the arrow . the the force . The SI unit for the . or strength . of forte is the newton ( This unit is named after the scientist and ( Isaac Ni . exert about mic ( iii when you litt small apple . Reading What SI unit is used to measure the strength , ot a force ?

Combining Forces Often . tUt than at single force act on an at one Lime . When an is to two or more threes ill . the result is the . the forces . The ( an ) is called the force . The net ( an object and in which direction it . When two or ' in the . the net force is found by adding the strengths of the individual forces . In Figure the lengths til the two , are added together lu tind the nut . Thi net force act in the its the ' When two or it ) act in opposite directions . the net in ' found by adding the ' forces . you must the ' Cli ( Adding 31 acting in one to i ! torn in the opposite direction is the same 115 adding it number to negative number . The net force acts in the direction of the greater force . It the ing strength , there is no net . FIGURE Forte and Motion The tom 01 the kick changes the direction sorter ball . FIGURE Combining Forte Vectors the strength and direction of the individual forces determine the net tom . How do you find the net forte when two forces act in opposite ?

Two forces acting in the same a larger net tone than either original . Two unequal tort acting in opposite directions produce a net in the direction at the larger force . ion Equal but opposite forte may name ! each other and no net torts Chapter 10 375 Unbalanced Forces In the sum ! in ! 0999 ' wo fame in , When two forces an in opposite directions , the net me tone , 91 tone is the between the two individual fume me he , moves the gym forces The box moves to the . Unbalanced Forces Whenever there is a net force acting on object . the forces are unbalanced . forces will cause the velocity ofan object to change . The object can speed up . slow down . or change direction . Unbalanced forces acting on In object result in I net force and cause change in the object velocity . Figure shows two people exerting forces on a box . When they both push a box to the right . their individual forces add together to produce a net force in that direction . Since forces act on the box . there is a net force and the box to the right . When the two people push the box in opposite directions , the net force on the box is the difference between their ual forces . Because the boy pushes with greater force than the girl , their forces are unbalanced and ! net force acts on the box to the right . As it result . the box moves to the right . Indian What is the result of unbalanced forces acting on An object ! Go 31 Balanced Forces In a between two people . each person pulls on opposite ends of the rope . If each person pulls ' i ' with equal force . neither the rope nor the people will move . on one object in opposite directions are . 3760

Unbalanced and Balanced Forces when the forces acting on an object are unbalanced , a net force acts on the object . The object will move When balanced forces act on an object , no net force acts on the object . The ob ect motion remains unchanged . Predicting If both girls pushed the box on the same side , would the motion of the box change ?

Why or why not ?

individual Fonts in Oposite when two equal forces act in opposite directions they cancel eath other out . The box doesn move . When equal forces are exerted in opposite directions . there is no net . Balanced forces acting on an object do not change the object velocity . In Figure when two people push on the box with equal fora in opposite directions . the are balanced . The box does not . Assessment target Reading Skill Take Notes Review your Calculating You run 41 oi 41 UNIT notes lot this section . What an two important desk . Your friend exerts a force it in ideas that you noted under Combining Forces ?

the same direction . What net force do you and your friend exert un the desk ?

Reviewing Key Concepts . Defining What is force ?

Explaining is a torus ?

Diagrams In at , one . arrow is longer than the arrow . on , Mo ' 3501 isms cards upright on a surface so that their top um I a . Reviewing How can you the net on edge tun on in or it two act in ?

forces , explain to a family member why the UNIT . Comparing and Contrasting How do cards are able to stand by themselves . Then push balanced es acting on an ) its one ( Explain to a family member the motion ?

How do unbalanced forces acting role at unbalanced forces in what happens , on an object its motion ?

Gamer to 317 Sticky Sneakers . Problem Friction is a force that opposes an object motion . Friction can be useful . For example , friction between sneakers and the ground can help an athlete to start and stop running . How does the amount of friction between a sneaker and a surface compare for different brands of sneakers ?

Skills Focus controlling variables , interpreting data Materials I three or more different brands of sneakers I spring scales , and , or force sensors mass tape large paper clips balance Procedure . Sneakers are designed to deal with various friction forces , including these starting friction , which occurs when you start from a stopped position friction . which occurs when you come to a forward stop I friction . which occurs when you come to a sideways stop Data Table Consumer Lab . Prepare a data table in which you can record each type of friction for each sneaker . Place each sneaker on a balance Put masses in each sneaker so that the total mass of the sneaker plus the masses is . Spread the masses out inside the sneaker . Tape a paper clip to each sneaker and attach a spring scale to the paper clip . If you are using force sensors , see your teacher for instructions . To measure starting friction . attach the paper clip to the back of the sneaker friction , attach the paper clip to the front of the sneaker friction . the paper clip to the side of the sneaker Starting Friction ( Friction ( Friction ( A 37 !

. The force necessary to make the sneaker start moving is equal to the starting friction force . To measure starting friction , pull the sneaker backward until it starts to move . Use the spring scale first . If the reading is less than , use a scale . Record the starting friction force in your data table . To measure either sideways or forward ping friction , use the spring scale to pull each sneaker at a slow , constant speed . Record the stopping friction force in your data table . Repeat Steps for the remaining sneakers . Analyze and conclude I . Controlling Variables What variables are controlled ?

Explain your answers . What are the manipulated and responding variables ?

Explain your answers . See the Skills Hand book to read about experimental variables . Applying Concepts Why is the reading on the spring scale equal to the friction force in each ease ?

Interpreting Data Which sneaker had the most starting friction ?

Which had the most friction ?

which had the most friction ?

Drawing Conclusions Do you think that using a sneaker with a small amount of mass in it is a fair test of the friction Why or why not ?

Hint Consider that sneakers are used with people feet inside them . Why did you pull the sneaker at a slow speed to test for stopping friction ?

Why did you pull a sneaker that wasn moving to test Starting . Drawing Conclusions Can you identify a relationship between the brand of sneaker and the amount of friction you observed ?

If so , describe the relationship . What do you observe that might cause one sneaker to grip the floor better than another ?

I . Communicating Choose one of the brands of sneakers that you tested . In a paragraph . explain why this sneaker is the best one to wear while playing a particular or activity . Be sure to include the results of this lab in your explanation . Design an Experiment The strength of the friction force is determined by both the design of the sneaker and the type of surface it presses against . Design an experiment to lind out how various types of surfaces affect the force of friction acting upon the sneaker . Obtain your teachers permission before carrying out your investigation .

9960 ! Students know when an tablet ! is subject to two or more at once . the is the cumulative of all the Students know how to identity separately the two or more that are acting on a single static obiect , including gravity , elastic due to tension or compression in matter . and What factors determine the strength of the Indian between two ?

what actors affect the gravitational force between two objects why do accelerate fall ?

When Is matter considered to he elastic ?

Key Terms I friction ' static friction sliding rolling friction fluid friction gravity mass ' weight free fall ' air resistance I projectile I compression tension Friction , Gravity , and Elastic Forces in Standards The Flexible Meter Stick . Place a meter stick across two desks so that it spans the gap between the desks . Rest a book on top of the meter stick . Using another ruler . measure how much the meter stick sags under the weight . Place another book on top of the first book . Measure how much the meter stick sags under the weight at two books . Think It Over Observing Did the meter stick sag more with two books resting on it ?

Why ?

Why does the meter stick break ?

Have you ever pulled your little sister in at up the side of a hill and then watched as she raced down it ?

you ever thought about some of the lotus at work ?

The tension in the rope allows you to apply the force necessary to pull the up the hill . causes the sled tu down the hill . Friction ultimately brings this to a stop at the bottom of the hill . All the while the snow is compressing under the weight . You will learn about friction . gravity , compression . and tension in this chapter . friction and gravity act on the sled .

Flour Friction and Smooth The smooth surfaces of the skis make for a last ride for these Finnish . Relating Diagrams and Photos How does the direction of friction ( ampere to the of motion ?

Friction A ( sitting at the end of a long table and asks to your book You slide it toward . hut it slows down and stops it reaches . Why does it up sliding ?

A force called friction acts in direction opposite to the motion of . Friction is it force that two ex on other when they rub against each other . Without friction or another force . a moving will not slop until it strikes another . The Causes of Friction In . duce less than rough surfaces . A piece of metal may quite smooth . But , as you can set in Figure even haw irregular . bumpy surfaces . irregularities of one surface come into Contact with those of another surface . friction The strength of the force of friction depends on types of surfaces involved and on how hard the surfaces push together . The skiers in Figure it last ride because there is very little friction between their skis and the snow , The reindeer would not be able to pull them easily over a rough surface such as sand . Friction also increases if surfaces push hard against other . If you rub your together , there is more friction than if you rub your hands together . FIGURE A Smooth ?

If you look at the polished of an aluminum alloy under a powerful , you find that it is actually quite rough . Chapter 10 381 , Activity Spinning Plates Vou can compare rolling friction to sliding friction . Stack two identical pie plates together . Try to spin the top plate . Now separate the plates and the bottom of one pie plate loosely with marbles . Place the second plate in the plate with marbles . Try to spin the top plate again . observe the results . Drawing Conclusions How does sliding friction compare to rolling friction ?

How do you know ?

Is it possible to get the top plate to spin forever ?

Online as ' For on friction Visit Web Code 3310 Static Friction Four types of friction are shown in Figure . The friction that acts on objects that are not moving is called static friction . Because of static friction , you must use extra to start the motion of stationary objects . For example . think about what happens when you try to push a heavy desk across a floor . If you push on the desk with a force less than the force of static friction between the desk and the floor , the desk will not move . To make the desk move , you must exert a force greater than the force of static friction . Once the desk is ing . there is no longer any static friction . However . there is another type of friction . Sliding Friction Sliding friction occurs when two solid surfaces slide over each other . When an object pulled at a constant velocity across a level surface , the pulling force equals the sliding friction . This is another example of balanced forces Sliding friction can be useful . For example . you can spread sand on an icy path to improve your footing . Ballet dancers apply a sticky powder to the soles of their ballet slippers so they wo slip on the dance floor . And when you stop a bicycle with hand brakes . rubber pads push against the metal rim of the wheel , causing the wheels to slow and eventually stop . Rolling Friction When an object rolls across at surface , rolling friction occurs . Rolling friction is less than sliding tion for similar materials . This type of friction is important to engineers who design skates . skateboards , and bicycles which need wheels that move freely . Engineers use ball hearings to ' reduce the friction between the wheels and the rest of the prod . These ball bearings are small . smooth steel balls that reduce friction by rolling between moving parts . Fluid Friction Fluids . such as water . oil . or air , are materials that easily . Fluid friction occurs when a solid object moves through a . Fluid friction is usually less than sliding friction . This is why the parts of machines that must slide over each other are often bathed in oil . In this way , the solid parts move through the instead of sliding against each other . When you ride a bike . friction occurs between you and the air . Cyclists often wear streamlined helmets and specially designed clothing to reduce friction . i ( What on two ways in which friction can he ?

Types of Friction Types of friction include static , sliding , rolling , and friction . Making Generalizations In does friction act compared to an object motion ?

Static Friction To make the sled move . the first has to overcome the force at static friction , Static friction acts in the opposite direction to the intended motion . Sliding friction Direction of motion Sliding Friction A Once the sled is moving . it slides over the floor . Sliding friction acts between the sled and the floor in the opposite direction to the sled motion . Static friction Intended direction of motion Rolling Friction Rolling friction occurs when an object rolls over a surface . For the skateboarder , roiling friction acts in the direction opposite to the motion . Direction of motion Fluid Fluid Friction A when an object pushes aside . friction occurs . The surfer must overcome the friction of the water . Direction of motion friction

Gravity When you drop a ball , it falls down . Have you ever thought about why it falls down and not up ?

One person who thought about it was Newton . He concluded that a force acts to pull objects straight down toward the center of Earth . This force is called gravity . Gravity is a force that pulls objects toward each other . Newton realized that gravity acts everywhere in the universe , not just on Forth . is also the force that keeps the moon orbiting around Earth . It is the force that keeps all the planets in our solar system orbiting around the sun . What Newton is now the Universal law of Gravitation . The Universal Law of Gravitation states that the force acts between all objects in the verse . This means that any two in the universe . without exception . attract each other . You are attracted not only to Birth but also to all the other objects around you . Earth and the objects around you are attracted to you as well . However . you do not notice the attraction among objects because these forces are small compared to the force of Earth attraction . Mass and Distance The force of gravity between objects increases with greater mass and decreases with greater distance . The measure of the amount of matter in an object is its mas The unit of mass is the kilogram . One kilogram is the mass of about 400 modern pennies . Look at Figure The more mass an obiect has . the The Cove , fa , the Pool beam , greater its gravitational force . Because the suns mass is so gravity is pulling her toward the great . it exerts a large gravitational force on the planets . 55 ' This causes the planets to orbit the sun . The force of gravity acts between all objects . Gravity Between Objects Gravity , and If mass . the force at gravity increases . decreases with distance . Inferring What happens to the force of gravity between two objects it the distance between them If distance . the force of gravity decreases . 3840

addition In tum on . The ' apart two ' tom . lulU . Iran toward . pull the ( from ' pull If . I . and the ' is Mun . Gravity and Weight fon ' at the at a planet known as weight . you step on scale , you are determining the un you . will have i You can the rut an object using st . Weight Mass Acceleration due to gravity is in and mass in . The I dun to is at ' tua example , at ill weighs 30 . 491 ) weight with the strength til the farce . he of the lam ' on an person by sixth uf the by . yuu on Earth to be 450 . you It the and . You would about 01 one sixth your wright on . You less on the moon ( the . is truly ' Rood rig pom ! What is the difference between weight and mass ?

Skills Activity Calculating You ( an determine the weight of an object If you measure Its mass . Estimate the weight of tour . Hint A small lemon weighs about . Use a balance to fund the mass of each . If the measurements are not kilograms . them to kilograms . Use the formula on this page to fund the newtons . How close to actual values were your noun Mass and Weight Thu astronaut jumps easily on the moon Comparing and Contrasting How do hu mass and on the moon compare to man and weight on Earth ?

Astronaut In Weight on Moon 270 Weight on Earth Mass on Moon Mass on Earth a Gravity and Motion drop hall . it ( might . hall , it out . morn drops ( and air are the ) re pon for thew . Free Fall the ' on an Ul ) il ' is said to Ill fall . Au in ' the force uf gravity alone causes an object to accelerate in the downward direction . muth ' I ' as they lull ?

a ( ration dun is . I for try ( It . an i lop ul building . 10 . Free Fa gnu , ha , i , he only , In , After two velocity is ) mu with masses lall . um I . In he 53 ' ax All in all stun . I hit that run ( at . al Figure Ill . The hull an tight has than hall on lull . lull ( Free Fall The graph shows how the speed of an free fall changes time Use the graph to answer the . Interpreting Graphs What IS the speed of the ( at I ?

At seconds ?

the slope ol the graph , iv , What does the number represent ?

Use the slope that you calculated Step to the ( Speed at I . The graph has a ' constant slope . What does the slope tell you about the ( motion ( seconds ) 386 Air ( Air Resistance In . where there is nu air . all tall with the mute oi . Su why due any nak , drops ?

A Hid am nIN through but that ad in the lu . i tum on . with . an ' Ax mil . lad ! talk more than an ha ' Yuu tan we ' paper and crumpled piece paper at the same tum . though Inn ' it ' and . In ( LI ! Projectile Motion than halt straight what ' VI . that i it projectile ! that is ! on the mutt dropped ! an . Thu . Imn at mum 21 the red ball WA , hall . continue to act on It sum ' it Act an the red lull . the the . I ! How does gravity that are moving horizontally ?

noun 11 Air Resistance greater area more an If the leaf and the atom fall from the tree at the same thus , the Morn witl first . and the lat ! um ' one wilt ( urn ?

Why ?

Haunt Projectile Motion One halt ' dropped and a ?

at the same turns Docs rhe of the bail how ! at ) Why 10 337 Elastic Forces When you squeeze sponge . the of the sponge come together , but it does not break . pull on i pair of gym shorts . you stretch the waistband . It break either . Why the sponge and the waistband break ?

They are elastic . Mutter is considered elastic if it returns to its original shape after it is squeezed or stretched . and tension are two types of elastic forces . Compression is an elastic force that or pushes matter together . When you sit on at couch . you exert a compression force on the cushion . The cushion comes close together and pushes back with an equal compression force in the opposite direction . The forces are balanced . You do move after you sit down the force of the ' pushing up balances your weight pushing down . An elastic force that stretches or pulls matter is called tension . at Figure 13 . A shoe hanging from the line on a Tension pole exerts a downward tension force on the line . the Tension ' i same time , the pole exerts an equal upward tension forte ir ions . es , do Ha because the on the . line . lint is in both dots are not move up or down the upward force of tension Photos what form the shoes weight . Other examples of tension are the strings he on at guitar and the cables holding up it suspension bridge . the line ?

Assessment Vocabulary Skill Latin Word Origins Review the . Describing How the mass of an object word origins of and tension . How do affect its acceleration during free fall ?

the word origins help you tell the Applying What changes Ill ! Words ?

when a sky diver parachute opens ?

What Key force stays the saline ?

A . Listing What are two forces ?

HINT . in summarizing factors the Applying ( mums a between two ?

ti ' HINT ?

I in i i Classifying What types occur when you ride a hike through a puddle ?

What is the law of universal I ing in ( CE gravitation ?

Explaining mass and distance affect Suppose Earth the force of gravity ) force were decreased by half . I How would your weight on How would this dung affect I of the surface of an whose paragraph art . mill ' Reviewing does an obiect accelerate would be different . when it falls toward Earth surface ?

A lo Students know that when the forces on an object ave , the object will change its ( that I ) speed up . slow down , or change direction ) Students know the greater the mass of an ) tho more lotto IS needed to the same rate ol change I what is Newton first law of motion ?

What is Newton second law of ?

Key Term I inertia Isaac Newton Newton First and Second Laws What Changes Motion ?

Stack several metal washers on top of a toy ( at . Place a heavy book on the near the ( at . Predict what happen to both the car and the washers if you roll the car into the book . Test your prediction . Think It Over Observing What happened to the ( at when it hit the book ?

What happened to the washers What force ( could account for any between the motions of the car and the washers ?

and why move as they do has scientists for thousands of years . the early ( Italian ( suggested that . is in . turn is only In the motion of an . A Im is not to it muting . ideas ' way ( Newton proposed the three laws in the late ( The First Law of Motion Newton lirst law about fora motion . Newton first law of motion states that an object will remain at rest or moving at constant velocity unless it is acted upon by an unbalanced force . An unbalanced force will Lana an to speed up , slowdown , or . at ( on it . The clothes on the floor of your mom will stay there you pick them up . You the force to mutt ) A tennis ball the air ( you hil it with at . moving . such 21 the ball , will at a until force acts to its speed or direction . gravity and an forces that will change the tennis hall as it through the . i

! Inertia The inertia of the objects on the table keeps them from moving . Inferring Why the girl use a slippery tablecloth ?

Around and Around An object moving in a circle has inertia . Tape one end of a length ol thread ( about ) to a table tennis ball . Suspend the ball in front you and swing it in a horizontal . keeping it above the floor . Let go of the thread and observe how the ball rolls . Observing how the ball moves when you let go of the thread Explain why it moves in this way . 3900 Inertia an object is moving or not . it resists any change to its motion . Galileo concept oi the resistance to a change in motion is called inertia . in i of an object to resist a change in motion . Newton ?

lirst law of motion is also the law of inertia common , such as why you move forward in your seat when a car stops suddenly . When a car stops . inertia keeps you moving . A force , such as the pull of a hell , in required to your motion . Inertia Depends on Mass Suppose you need to an empty aquarium and an aquarium lull ul ' Obviously , full aquarium is harder to move than the empty one . because it has more ( greater the mass of an object is , the greater its . and the force required to change its motion . The full aquarium is more to mow because it ' than the empty . How is moss related to Inertia ?

The Second Law of Motion Suppose you arc two children who love wagon . Their favorite part is when you quickly . Recall Lhat is the mic at which velocity changes . When you get tired and sit in the wagon , one ofthe children pulls you . He soon finds he can not accelerate the wagon nearly as fast as you can . How is acceleration related to the pulling it ?

How is the acceleration to tho ?

Changes in Force and Mass How do you got wagon to speed up . slow down , or turn corner ?

You apply ! force to it . What if you want the wagon to speed up . slow down , or turn corner at a faster rate ?

You apply even more force . An in force results in an in ration . Another way to increase acceleration is to change the mass . Suppose your friend gets into the wagon with you . The wagon now has more mass . the child pulls with the same as . the wagon will move very slowly . if at all , For a force . an ( in tin mass will result in decrease in the acceleration . Determining Acceleration second law of motion states that acceleration depends on the net force acting on the object and on the object mass This ship run be written as a formula . Net force Acceleration Ma Acceleration is in meters per second per second ( net form is in ( and mass is measured in kilograms ( You can also write this formula as Nut force Acceleration . You can think of newton in the force to give a muss an ( i ( of . Fellini what does the of an object depend , upon ?

Go More on Newton laws Visit Wet Code 15 Force and Mass The force ol the boy pull and the mass of the wagon determine the wagon acceleration . more mass is added to the wagon and if the boy pulls with the same force , how will its change ?

Math Algebra I Sam ) Math Calculating Force A speedboat pulls a . The skier accelerates at . Calculate the net force that causes this acceleration . Read and Understand What are you given ?

Mass of the ( 55 Acceleration of the ( a ) Plan and Solve what quantity are you trying to calculate ?

The net force ( I ' What formula contains the given and the unknown quantity ?

or , Math ( Perform the calculation . gnu , 55 10 . Calculating Force What is the , accelerating at ?

Calculating Force What net I Back and Check force is needed to accelerate Does your answer make sense ?

a cart at 14 ?

A net force of 110 is required . This does not Include the force that overcomes friction . Assessment Vocabulary Skill Latin Word Origins The Applying Concepts Explain why a car inertia comes from two Latin meaning not with a large might more than and um ' or How dues car with smaller both the word origin help you remember the term ?

cars drive the same distance . Reviewing Key Concepts HINT . Reviewing What law ?

inn , Explaining lint law call the law ?

Calculating Force What is the Us inertia to explain why you feel 09 ( We 09 back into the gent ola car when it accelerates 32 ( a . Defining State . cuuld you an ' i saint if the force on the ill ! 07 30 ( 37 were ?

that has a net force of acting upon it . sue sin Students know that when the forces on an object are , the object will change its velocity ( that is . it will speed up . slow down . or change direction ) What is Newton third law of motion ?

How can you calculate the momentum at an object ?

What is the law of conservation of momentum ?

Key Terms I momentum law of conservation of momentum Newton Third Law How Pushy Is a Straw ?

a rubber band around the middle of the front cover of a hardcover book , Place four marbles in a small square on a table . Place the book on the marbles lace up so that the cover with the rubber band is on top . Hold the book steady by placing one index finger on the spine . Then , as shown , push a straw against the rubber band with your other index finger . Push the straw until the rubber band stretches about to . Then let go of both the book and the straw at the same time . Think it Over Developing Hypotheses What did you observe about the motion of the book and the straw ?

Write a hypothesis to explain what happened terms of the on the book and the straw . Have you ever tried to touch A him to ' hard if you are both wearing skates . When your pushes you to gel . you move too . And when your friend runs into you to stop . you both end up moving ! To why this you to know about third law of motion and law ( Ill of . Newton Third Law of Motion Newton proposed that whenever om exerts a force on object , the St ' exerts a hack on the first object . The force exerted by the second object is equal in strength and opposite in direction to the force . Think of one force as the and the other force as the Newton third law of motion states that if one object exerts a force on another object , then the second object exam I force of equal strength in the opposite direction on the object . Another way to state third law is that for every action there is an equal but opposite reaction .

When the gymnast does a flip , he pushes down on the vaulting horse . The reaction force of the vaulting horse pushes him up to complete the flip . I Anton when the dog leaps . force it pushes down on the ground . The reaction force of the ground pushes the Reaction dog into the air . forte noun 16 Pairs pairs explain how a gymnast ( an over a vaulting horse . how kayaker can move through the water , and how a dog can leap of ?

the ground . Interpreting Photos how the velocities ol the gymnast , the kayaker , and the dog ( hang as a result of reaction ( ones . 3946 The er paddle pulls on the water . The reaction force of the water pushes back on the paddle , causing the kayak to move . Pairs You iar with many examples of Newton third law . Pairs and reaction are all around you . When you jump , you push on ground with your lost . This in an action force . The ground pushes on your feet with an equal and site force . This is the reaction force . You up and in an direction you jump ground is pushing you ! In way . the speeds up by exerting an action force on the with water pushes on paddle with an ' i that propel the . Now you can what happens when you teach your friend to rollerskate . Your friend action fort when pushes against you to ' You exert a in the direction . a result , both til you speed up in oppo ( lions . Detecting Motion Can you always detect motion arc in action ?

liu ( i no . gravity pulls on an object , you can not detect the equal and of . you drop your . Gravity pulls the ward . Al saint time . the pencil pulls Earth upward with an and ' force . You see Earth accelerate toward the pencil Earth inertia is so that its too small to notice .

Do Forces cancel ?

Earlier you learned that if two equal forces act in opposite directions on an object . the forces are balanced . Because the two add up to zero . they each other out and produce no change in velocity . Why then do the action and reaction forces in third law of motion cancel out as well ?

After all . they are equal and opposite . The action and reaction forces do not cancel out because they are acting on different objects . look at the volleyball player on the left in Figure 17 . She exerts an upward action force on the ball . In return , the ball exerts an equal but opposite downward reaction force hack on her . The action and reaction forces act on different objects . On the other hand . the volleyball players on the right are both exerting it force on the same volleyball . When they hit the ball from opposite directions . each of their hands exerts force on the ball equal in strength but opposite in direction . The forces on the volleyball are and the ball does not move either to the lelt ot ' to the right . Ruins . Why do onion and ( oral cancel each , other ?

Foam 17 Forte on wrists Forte on all Field Trig ) Il FORE ! Forms In the photo on the left , the player wrists exert the action force . In the photo below , the ball exerts reaction forte on both players . Interpreting Diagrams In the photo below , will the volleyball velocity ( hangs ?

Why ?

. Calculating Momentum A golf ball travels at 16 , while a baseball moves at . The mass of the gall ball is and the mass of the baseball is . which has greater momentum ?

Momentum What is the momentum of a bird with a mass of flying at 15 3960 Momentum All moving objects have what called a quantity of motion . Another name for this quantity is momentum . Momentum ( moh tum ) is a of a moving object that depends on both the mass and the velocity of the . You can calculate the momentum of I moving object by multiplying the object mass and velocity . Momentum Mass at Since mass is measured in kilograms and velocity is measured in meters per second . the unit for momentum is per second ) Like velocity . acceleration . and force . momentum is by its direction as well as its quantity . 111 momentum of an is in the same direction as its velocity . Reviewing Math and Geometry ! Calculating Momentum which has more momentum a sledgehammer swung at , or a sledgehammer swung at ?

Read and Understand What information are you given ?

Mass at smaller sledgehammer Velocity of smaller sledgehammer Mass of larger Velocity ol larger sledgehammer Plan and Solve What are you trying to calculate ?

The momentum of each sledgehammer I What formula contains the given quantities and the unknown quantity ?

Momentum Mass Velocity Perform the calculations . Smaller sledgehammer . Larger sledgehammer Back and Check Does your answer sense ! it is possible or the hammer to have more momentum than the one because it has a greater velocity .

13 Momentum An object momentum is the product of the Ob ! mass and velocity . Problem Solving dogs have the same velocity . which one has the greater momentum ?

The more momentum a moving has . the harder it is to change its velocity . For example . it is easier to change the I Tim baseball moving at 20 mi than it is to change the velocity of a car moving at 20 . car has more tum it has a grater . It is however harder to change the velocity ofa baseball moving at 20 than it is to change the velocity of a baseball moving at mix . The baseball moving at 20 has more momentum because it has a greater velocity . colliding Cars . Find two nearly identical toy cars that roll easily . Make two loops out of masking tape ( sticky side out ) Put one loop on the front of one of the cars and the other loop on the bad of the other car . Place on the floor the car that has tape on the back . Then gently roll the other car into the back of the stationary car . How do each of the cars velocities change ?

Was momentum conserved ?

How do you know ?

Predicting What will happen if you put masking tape on the both cars and roll them at each other with equal speeds ?

Will momentum be conserved ?

Test your prediction . What must you to determine an object , momentum ?

Conservation of Momentum In everyday language . conservation means saving resources . You might conserve water or fossil fuels , for . cal , the word has a meaning . refers lo the before and after some event . An amount that is conserved is the same amount after an event as it was before . The total amount of momentum objects have is conserved when they collide . Momentum may be ' from one object to another as the velocity uf the objects change . but none is lost . This is called the law of conservation of momentum . The law of conservation of momentum states that , in the absence of outside forces . the total momentum of that interact does not change . The amount of momentum is the same before and after they interact . The total momentum of any group of objects remains the same . or is conserved . unless outside forces act on the objects . Friction is an example of an outside force .

Go ac Ve of Momentum In the absence of friction . momentum is ( when ' i two can collide . Interpreting In which ' diagram is all of the momentum transferred from the web ( blue car to the green ( ar ?

Mo Moving Objects Before , Before the , the blue car moves faster than the green tar . Afterward . the green car moves faster . The total momentum stays the same . Gone Moving Object when the green tar Belore is at rest before the ' collision . all of the blue car momentum is transferred to it . Momentum is ( conserved . After ) Mo Connected Objects Before mi lithe two cars together , momentum is still conserved . I Together . the an move slower than the blue car did before the collision . BIO

Target Reading sum Take Notes Review your ( Reviewing Key Concepts HINT Collisions with Mo Moving Objects In Figure , the blue train car travels at down the same track as the green train car traveling at only . The two train cars have equal masses . The blue car catches up with the green car and bumps into it . During the collision , the speed of each car changes . The blue car slows down to , and the green car speeds up to . Momentum is momentum of one train car decreases while the momentum of the other increases . Collisions With One Moving Object In Figure . the blue car travels at but the green car is not moving . Eventually the blue car hits the green car . After the collision . the blue car is no longer moving . but the green car travels at . Evert though the situation has changed . momentum is conserved . All of the momentum has been transferred from the blue car to the green car . Collisions with Connected Objects Suppose that . instead of bouncing other . the two train cars couple together when they hit . is momentum still conserved in Figure After the collision , the coupled train cars make one object with twice the nuns . The velocity of the coupled trains is the initial velocity of the blue car . Since the mass is doubled and the velocity is divided in half , the total momentum remains the same . Identifying What is meant of momentum ?

Inferring The total momentum of two marbles before a collision is . No notes for this section . What three important did you include about Newton Third law of Motion ?

total of the marbles after the . Reviewing State Newton third law of . HINT . mom ) collision . Hun Summarizing According to third law of motion , how are action and reaction forces related ?

INT . Applying Concepts A catches a ball ' while standing on roller skates . What 44 Momentum What IS he happens to the boy velocity and the hall momentum ' 37 ?

speed of 25 ?

nut a . Defining What in momentum ?

Calculating Momentum which has more momentum a dolphin swimming at , at a manatee swimming at ?

Predicting What is the momentum parked car ?

Relating Cause and Effect Why is it for drivers to allow more distance between their cars when they travel at faster speeds ?

outside forces act on the marbles . What is the Forced to Accelerate Problem How is the acceleration of a skateboard related to the force that is pulling it ?

Skills Focus calculating , graphing , interpreting data Materials I skateboard meter stick string stopwatch masking tape spring scale , several bricks or other large ( es ) Procedure . Attach a loop ol string to a skateboard . Place the bricks on the skateboard . Using masking tape . mark off a distance on a level . Label one end Start and the other Finish . Attach a spring scale to the loop of string . Pull it so that you maintain a ol Be sure to pull with the scale straight out in front . Practice applying a steady force to the skateboard as moves . Copy the data table into your notebook . 10 . Find the smallest force needed to pull the skateboard at a slow , constant speed . Do not accelerate the skateboard . Record this force on the first of the table . Add to the in Step . This will be enough to accelerate the skateboard . Record this force on the second line of the table . Have one of your partners hold the front edge of the skateboard at the starting line . Then pull on the spring scale with the you lound in Step . When your partner says Go and releases the skateboard , maintain a constant force until the skateboard reaches the finish line . A third partner should time how many seconds it takes the skateboard to go from start to . Record the time in the column labeled Trial . Repeat Steps and twice more . Record your results in the columns labeled Trial and Trial . Repeat Steps , and using a force greater than the force you found in Step . Repeat Steps , and twice more . Use forces that are and greater than the you found in Step . 4000

Analyze and Conclude . Calculating For eath force , find the average of the three times that you measured , Record the average time in your data table . For each forte . find the average speed of the skateboard . Use this formula Average speed Average time Record this value for each force . Calculating To obtain the speed of the skateboard . multiply each average speed by . Record the result in your data table . Calculating To obtain the acceleration , divide each speed you found by the average time . Record the in your data table . Graphing Make a line graph . Show the force on the and the on the The should go from to 10 NA The scale should go from to about . If your data points seem to form a straight line , draw a line through them . Interpreting Data Vour first data point is the pulling force required for an acceleration of . If the acceleration is zero , what is the net force on the skateboard ?

Explain . Interpreting Data According to your graph . how is the of the skateboard related to the pulling force ?

Communicating Write a paragraph in which you identify the manipulated variable and the responding variable in this experiment Explain why the mass of the skateboard is kept constant . See the Skills Handbook to read about experimental variables . Design an Experiment Design an experiment to test how the tion of the loaded skateboard depends on its mass . Think about how you would vary the mass of the skateboard . What quantity would you need to measure that you did not measure in this experiment ?

What quantity would you keep con stant ?

Do you have the equipment to make that measurement ?

If not . what other equipment would you need ?

Obtain your teacher sion before carrying out your investigation .

Section Integrating Space Science Rackets and Satellites , Stand Up Students know that when wha Obie Move the ferret on an are In Circle ?

mud . the will mange its velocity ( that is . it wilt speed up . slow down . or change ) Tie a small mass , such as an empty thread spool to the end of a string no more than one meter long . new dog a yu ( ket on me . Swing the object around in a circle that is ground ?

perpendicular to the floor , Make sure no ( one IS near the swinging ob , and let it go ! KEY Think It Over satellite Observing Is there a net force acting on the centripetal forte object ?

How do you know ?

In October 1957 , Homer and saw a speck ! light across the sky . It was the Russian , first . It was into space by a rocket . This sight Hunter and his friends . spent thu next yours designing . building . and rockets in their hometown of , esl of their first attempts tailed . but they did not up . built a that soared to ( I of . hand work paid . In , they won first place in Fair . then . rocket launches have more . but they are still an some sight . Homer holds a rocket that he and his friends designed . 4010

How Do Rockets Lift Off ?

A space shuttle like the one in Figure It ) has of more than million kilograms when loaded with . An incredible amount of force is required to get the shuttle to overcome Earth gravity and rise into space . Rockets and shuttles lift into using third law of . They burn fuel and push the exhaust gases at a high velocity as they lift off . In turn . the gases push upward on the rocket . A rocket can rise into the air because the gases it with a downward action force exert an equal but opposite reaction force on the rocket . As long as this upward . called thrust . is greater than the downward pull of gravity . there is an unbalanced force in the upward direction that causes a change in the et velocity . As 21 result . the rocket accelerates upward into space . What Is a Satellite ?

Rockets are often used to carry satellites space . A satellite is any object that orbits another object in space . The moon in a satellite because it orbits Earth . An satellite is il device that is launched into orbit . satellites are designed for many purposes , such . military intelligence . weather and geographical surveys . Circular Motion satellites travel around ' Earth in an almost circular path . An object traveling in a , circle is constantly changing direction so it in mun ing . If an is , an unbalanced fora must A launch be acting on it . Any three that ati object to I ' in a circular path is a centripetal force ( ih ) gas The The word centripetal ! means The i reaction force at the force acts in a direction perpendicular to the gases sends the rocket direction the object is at anv given point , In the su the the rock ascends ' centripetal force . The string pulls the object toward ?

the miter . and thereby keeps it in at circular path . For a satellite , the centripetal force that pulls the satellite toward the center of Earth is gravity . What type of tone causes an object to , move in a circular path ?

Direction of throw eh . Forte of . gravity The ball Frame 21 . path beause . it moves forward A projectile follows a curved path . while Wu The horizontal and vertical motions act independently , FIGURE 22 Satellite Motion The faster a pro tile is thrown . the farther it travels before it hits the ground . A projectile enough velocity moves in a circular orbit . Interpreting Diagrams How does the direction compare to the direction of the orbiting projectile motion at any point ?

Satellite Motion Gravity pulls satellites toward . So why do satellites to the ground , as a ball thrown through the air would ?

The answer is that satellites have a greater horizontal velocity than a ball would have . Instead of falling to fall around Earth . If you throw a ball , as shown in Figure . the ball will move away from you at the same time that the unbalanced force . gravity . causes a change in direction , The horizontal and vertical motions act independently . and the ball follows a curved path toward the ground . you throw the ball faster , it will land even farther in front of you . The faster you throw a projectile , the farther it travels before it lands . Now suppose , as Isaac Newton did . what would pen if you were on a high mountain and could throw a ball as last as you wanted . The faster you threw it , the farther away it would land . But . at certain speed . the path of the hall would match the curve of Earth . Although the hall would keep falling due to gravity . Earth surface would curve away from the ball at the same rate . Thus the ball would all around Earth in a circle . as shown in Figure 22 . Satellites in orbit around Earth continuously full toward Earth . but because Earth is curved they travel around it . In other words . a satellite is a falling projectile that keeps mixing the ground ! It falls around Earth rather than into it . satellite does not need fuel because it continues to move ahead due to its inertia . At the same time . the unbalanced force . gravity . changes the satellite direction . The speed with an object must be thrown in order to orbit Earth turns out to be about !

Reviewing Key Concepts ii ?

Satellite Location Some satellites . such as ping and observation satellites . are put into low orbits of less than kilometers . in a low orbit . at trip around in less than two hours . Other satellites are sent into higher orbits . At those . a satellite travels more slowly . taking longer to circle . For satellites about Communications above Earth surface . At that height . they We Earth once every hours . Because Earth rotates once Glow every 24 hours . a satellite above the equator always , stays at the same point above Earth as it orbits . gravity help keep Research Flaunt 13 mo Locations ' Depending on their uses , satellites orbit at different heights . Section Reading Inferring in Figure 22 , is thrown with enough to orbit . What would happen if the wen thrown with a greater velocity ?

Assessment Vocabulary Latin Word How docs knowing the meaning of the mini origin of help you the meaning ?

Identifying Which laws of motion explains how a rocket lifts oil ?

Explaining How do pairs explain how at rocket lifts oft ?

Applying Concepts As a upward from Earth . air decreases with of gravity . The ' aim decreases as its fuel is med up , If thrust the affect the ?

Defining What is a satellite ?

Relating Cause and Effect What causes satellites to stay in orbit rather than falling toward Earth ?

333 , Swing the Bucket Fill a small plastic bucket halfway with water and take it outdoors . Challenge a family member to swing the bucket in a vertical circle . Explain that the water wo fall out at the top if the bucket is moving fast enough . Tell your family member that it the bucket falls as fast as the water , the water will stay in the bucket . Relate this activity to a satellite that also falls due to the unbalanced force of gravity . yet remains in orbit .

Chapter 10 Study Guide An lone will ( ause a change in an object . The Nature of Force ( Key Concepts , is by its and by in it nuts . Unbalanced on an in a net fort and dung an obit ( I . Bi ' fora aiding on du not change the . Key terms ) ui force fun ?

ction . Gravity , and Elastic Forces ( Key . Th the force in the type of ( i and on how hard the arc . with nim and with . In free fall . the force of gravity alone ( uses an In in tin . Matter is considered elastic if it to its shape It is , Key Terms friction static friction I sliding friction I i i ' weight I tree fall I all resistance tension Newton First and Second Laws ( Key Concepts an law States an will moving at it is acted upon by an force . law of motion that depends un nut fume acting the and un ( mass . Mass Key Term lid Newton Third Law ( Key concepts I Newton third law uf that it one tom , I . exert , force nI ' in the opposite on the first . You can calculate the momentum ivy multiplying the inns and velocity . Mans . The total . is , act on the . Key Terms of Rackets and Sate es Key concepts a I A can rise into the air the gash it with downward action an equal . lime mi the rocket . Satellite in orbit around Earth ) Earth , but is they travel around it . Key Terms

Review and Assessment Target Reading Skill . HINT Take Notes in your notebook . in ! include statements . Reviewing Key terms Choose the letter of the best answer . When an ) acts on an . the ' the or the . la . is by . not change the of the . 13 equal to the weight of the . Which is an . Whirl oi the is not ?

I . satellite is . thrown hall . the LI soaring . The resistance ! an in any in is inertia . friction . weight . The an object mass and is called the net . weight . Go Far . Visit ( om forte that two exert on other Strength depends on types of surfaces how hard they are pushed together Complete the following sentences so that your answers clearly explain the key terms . When people hot and the HINT doc nut inure . an ul forces . which are . Friction depends upon how hard lhe . A pulls ( an pushed tug and is called gravity , depends upon . I lie tum greater on at leaf amt I 10 . I he momentum an depends on . I , gin Science Descriptive Paragraph Suppose you have been asked to design a new amusement park ride . Write a description oi how you will design it . Explain the role that friction and gravity will play in the ride design . Chapter 10 407

Review and Assessment children pull on the my at the time , yet there is no not force on the toy . How is ( I , 12 . Ally are parts ol river each Ill nil ?

A is hanging motionless from a string . and forces exerted on . huw . ma are related by Newton second law motion . 15 . Suppose you Are an ' a space walk your space station when yu ur pack runs nut ul . can mu use your empty pack in get you back to the station ?

16 . Draw diagram showing the motion around Earth . Draw the fun vectors ting un the . the satellite ?

Thinking 17 . name force yuu on ti when il ?

18 . Applying You a ( when stud in a ( rank on the . Using the term . explain what . 19 . Problem Solving look at the ul pulling A hag equipment . The between the the is 15 ' is the url acting on the bag ?

is the of the bag ?

20 . Relating Cause and Ifyou push bank a table at a constant , is the friction furi . it than , equal In . in more than your pushing ?

4000 Math Practice 21 . Calculating Force A hall accelerates at me out ' What on the bowling ball ?

22 . Calculating Momentum . travel at 16 ink . The um of the driver is 75 . What is the momentum ol the driver ?

Apply Skills Use the illustration showing a collision between two balls to answer Questions . Before 23 . Calculating Us the momentum to find the momentum ball and the . the of each hall ( Inferring Find the total before rind collision . is the law ul ot momentum satisfied in this collision ?

25 . Designing an experiment in you is not conserved the halls when strong . Standards Investigation Assessment Test your vehicle to make sure it will work on the mac in your . Will the vehicle stay within the bounds set by your . all the acting on the vehicle . was the must til ( ITl tor your ?

at least three features you in the design vehicle that led to an in ) For . did you give it a smooth shape for low air resistance ?

Standards Practice Choose the letter of the best answer . Which til the following is by the force of gravity ?

A weight I momentum mass distance . When an object is pulled across a level surface at a constant velocity . what force is the pulling force equal to ?

A gravity I Friction inertia an unbalanced force . force makes it less likely for a person to slip dry sidewalk as opposed to an icy sidewalk ?

A air resistance inertia momentum Use the diagram below to answer questions and . What conclusion can you draw hy looking at the diagram ?

A Air resistance in front of the balloon pushes it backward . I Gravity forces air out of the open end . The force of the air leaving the balloon causes it to accelerate . Friction the acceleration to decrease . In the diagram above , why do the two forces cancel each other out ?

A They are not equal . They both act on the air . They both act on the balloon . They act on different objects . if Trucker at . The table below shows the mass of and net force on four objects . Which object has the greatest acceleration ?

Calculating Acceleration 100 20 20 Shopping cart 25 50 Book A boulder shopping can book in game , you pull on the with a force of to the right and your friend pulls on the rope with a force of to the left . What it the net force on the rope ?

A 200 to the right I 200 to the left I 100 to the right Etc idea I . dogs are pulling on opposite ends ofa bone . One dog pulls to the right with at force of 50 while the other pull to the left with El force of 40 Are the forces on the bone balanced or unbalanced ?

How do you know ?

What is the net force on the bone ?

Would the hone velocity change ?

Why ?

om