Focus on California 8th Grade Physical Science Textbook Chapter 9 Motion and Energy

Motion and Energy Standards Preview I The at ur object is the run of chance of its position As basis tor ( hi ! Students know position is defined in to some of Stan dud point and it set at ( average in total traveled by the total time and that the sneer ! at an Along the path traveled tan vary Students know how to solve . time , and average speed . students know the of mutt be dumbed by ( ing both the ma at the ab Students know In be due to . tints , or both Students know how interpret graphs of position versus um and graphs of speed versus Int a single Ii I made by ing and ( ing investigations . As a bails for understanding this ( urI ( epI and ing the In ( It other strands . students should their own and perform tions . will the slope at the graph as the constant in the try and apply principle in interpreting graphs data . between and nonlinear an a graph 01 data . The horses running . this ( In

, Mellon How can you describe an motion ?

Check What You Know You are in a stationary car and another car passes you . How would you describe the motion of the other car ?

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The images shown here represent some of the Key Terms In this chapter . Vou can use this vocabulary skill to help you understand the meaning of some Key Terms in this . Academic Words Knowing these academic words will help you become a better reader in all subject areas . Look for these words in context as you read this chapter . Example Sentence to by reasoning After investigating the . they concluded that everyone should wear a bicycle helmet . a series of numbers and The for for the area ol a cam luh ) symbols that represents a circle is 343 rule ad . the possibility that The student who is studying poh something will develop chemistry is a chemist . 360 in a certain way Apply It ! Choose the word from the table that best completes the sentence . The for finding the area of a rectangle is A . After waiting for 20 minutes , he that his friend was not coming . The heavy rains and rising river are a problem for people who live beside the river .

Chapter Vocabulary Section , ism motion point distance Section ) screed average speed instantaneous speed velocity slope Section Section ' work energy kinetic energy energy potential energy energy mechanical law 01 ( Build Science Vocabulary On Visit ( turn Web Code 335

How a pending Identify Main Ideas The main idea is the most important point in a passage of text . Sometimes the main idea is stated directly at the beginning or end of a passage . The main idea is supported by details and examples . Here are some tips to help you identify the main idea . Note the details in the passage . I Look for the connections among the supporting details . Then look for a sentence that pulls all the details together . Read the paragraph below and identify the main idea and supporting details . A measurement of distance can tell you how far an object travels . A cyclist . for example . might travel 30 kilometers . A sprinter runs 100 meters . An ant might walk centimeters . An ant walks centimeters . A cyclist travels 30 kilometers . Apply It ! Draw a graphic organizer like the one shown . Fill in the main idea and details . Then answer the following questions . What is the main idea in the paragraph ?

What is a good title for this graphic organizer ?

Complete a graphic organizer like the one above for the headings Calculating Speed in . Changing Velocity in Section , and Potential Energy in Section .

Standards Investigation . Show some Motion Vou are constantly surrounded by objects in motion . Cars , trains . buses . and airplanes carry people lrom one place to another . Baseballs . animals . and even the planets in the sky also move . How can you measure the motion you see ?

Your Goal In this investigation . you will identify the motion of several common objects and calculate how fast each one moves . To complete this investigation , you must measure distance and time accurately calculate the average speed of each object using your data prepare display cards of your data , diagrams , and calculations follow the safety guidelines in Appendix A Plan It ! With your classmates , brainstorm several examples of objects in motion , such as a feather falling , your friend riding a bicycle . or the minute hand moving on a clock . Choose your examples and have your teacher approve them . Create a data table for each example and record your measurements For accuracy . repeat your measurements Then calculate the average speed of each object . Make display cards for each example that show data , diagrams . and calculations

00 Describing Motion cA Standards Student know position is defined in relation to some ( at a standard point and a set of dIVE ( when I an ( in motion ?

What IS the between and Key Terms I motion point I distance I displacement I How Fast and How Far ?

a stopwatch , find out how long it takes you to walk meters at a normal pace . Record your time . Now choose a starting point and find out how far you can walk in seconds at a normal pace Record your distance . Repeat Steps and , walking slower than your normal pace . Then repeat Steps and walking faster than your normal pate . Think It Over Inferring What is the relationship between the you walk , the time it takes you to walk , and your walking speed ?

How do you know ifyou ( lFyou ' I ' on at train , you know you can not ' arc in motion Looking til building outside the window helps you . the building St ' in past the train . it you and the train that are moving . you i ' min that to be moving . is train . or ' train ?

How do you tell ?

Motion Him do you decide if an is ?

Yuu are probably sitting in chair as yuu read this bank . Are you moving ?

Your eyes and ' up and . But you would probably are is in motion if its ( i , yuur div yuur chair is not changing , you conclude you are not in motion . Points it you are moving . yuur chair in point . A reference point is place ur ' used tut lo ii is in motion . An object is in motion if it changes position relative to a reference point . that we all Ir ) tree , a . ur at good paints . Frum the of i ( of train in Figure sud ! an not in motion . If the pass is moving relative to tree . he can conclude that the train is in . Once you ' yuur I ' I ( um in position by using a pin or I ) sign . The signs or run pair of opposing direction ruin the paint . In the right and . up down . away rum and toward . or in behind . it you the , on the train your point . then three seats in UK him couid be shown as . A uf would mean seats behind him . What is a reference point ?

Flaunt Reference Points The passenger ( an use a tree as a reference point to decide ifthe train is moving , A tree makes a good reference point because it is stationary from the passenger point oi view . Applying Contents Why is If to choose a stationary object as a ( point ?

Relative Motion Whether or not an object is in motion depends on the reference ( and Contrasting Are the skydivers moving i relative to the airplane from WhI ( they moving relative to the ground ?

Relative Motion from the Plane The plane does not appear to be moving , I The appear to be moving away . A point on the ground appears to be moving away . Relative Motion From the ' The plane appears to be moving away . The do not appear to be moving . The ground appears to be moving closer . Relative Motion Arc you moving as you read this book ?

The on your point . your chair is your point , you are not . But il you chow point . you he moving . Suppose you choose the sun as a reference point of your chair . if you compare sun , you are moving quits rapidly . This in because you aml your chair arc on Earth , which ' a sun . Earth move about 30 kilometers every second . So you . your chair , book , and elm on quickly ) well . Going that lust , you could New York City lo Lu in about Relative to the run . both you and your chair are in motion . But you arc moving with Earth . you do not in moving . Distance and Displacement ' you . the you and a ' ence point changes . Distance is the length of a path two points , in Figure ITEM the route you take to school each . From your starting point ( home ) you walk one block . turn left , and li ) Then you and walk my block . you turn and walk final blocks to your uni ( school ) The plane appears to be moving across the sky . The skydivers appear to be moving closer , The ground does not appear to be moving . Relative Motion from the Ground

How many blocks did you walk in all ?

The lengths of the segments of your walk are block . block . blocks . and blocks . Therefore . your walk from home to school is a total distance of blocks . Now look at the red arrow in Figure it shows the displacement from the starting point . Displacement is the length and direction that an object has moved from in starting point . Distance is the total length of the actual path between two points . Displacement is the length and direction of I straight line between starting and ending points . According to Figure you walked a ( low lines ) of blocks . but your ( red arrow ) was blocks northeast . As you learn about motion . you will other that also have a magnitude , or size . and at tion . A quantity that consists of both a magnitude and direction is called a vector . Displacement is a vector . but distance is not . Other examples of vectors include ity , acceleration , and will learn about these later in this book . Vectors are shown cally by using an arrow . The length of the represents the vector magnitude . The direction of the arrow indicates the direction of the vector . What is displacement ?

FIGURE Distance and the yellow lines show the distance between home and school along a path . The red arrow shows the displacement between the same two points section Assessment Vocabulary Words content An object moves to the nu Describe a in which you have used a right , then to the left , then to the . What is the object displacement reference point to determine your relative motion . from its origin ?

Use the word in your explanation . Reviewing Key Concepts . El How do you know if an is moving ?

Explaining Why is it to know if your reference point is moving ?

Applying Concepts Suppose you are riding in a car . Describe your motion relative to the car . the mad , and the sun . a . Defining What is displacement ?

Comparing and Contrasting How are distance and displacement similar ?

How are they different ?

333 ' Walkabout Place a penny or other marker on the or ground to show your starting point . Then walk a few steps in one direction and a few more in another . Use a ruler to estimate the distance that you walked and your from the starting point . How do these values compare ?

09 Students know that average speed is the total distant traveled divided by the total time elapsed and that the speed of an omen along the path traveled can vary . Students know how problems involving distance , time , and average speed . Students know the velocity of an must be described by specifying both the direction and the speed at the How do you calculate speed ?

How can you changes in ?

How ( an you interpret graphs of distance versus time ?

Key Terms I speed I average speed I Instantaneous speed I velocity I slope 3420 Speed and Velocity Standards How Slow Can It Flow ?

Put a spoonful of honey on a plate . Place a piece of tape train the bottom edge of the honey . Lift one side of the plate just high enough that the honey starts to flow . Reduce the angle until the honey barely moves . Prop up the plate at this angle . Time how long the honey takes to rea ( the tape . Predict how far the honey would move in twice the time . Think Over Forming Operational Definitions When an object appearto be moving at first glance , how can you tell if it is ?

A can tell how far an object travels . A cyclist . might trawl 30 . An ant might travel centimeters . If you know the distance an travels in certain amount of time . you can calculate the speed of is it of rate . A tolls you the something that occurs or changes in one unit of time . The speed is the distance the travels per unit ul Calculating Speed ( To calculate the speed of an object . divide the distance the object travels by the amount of time it to travel that distance . This I ) can be written as an equation . Distance Time The speed equation ul ' unit ul divided by unit ultimo . lfyou . in meters and time in seconds . you express speed in meters per second . or The ' I is read i lfyou distance in and time in hours , you express speed in . per hour , or . For example . at who travels 30 kilometers in hour has at ( ul 30 . ant that in I second is moving at a speed of centimeters per second . or .

Average Speed The speed of most moving objects is not constant . The cyclists shown in Figure , for example . change their speeds many times during race . They might ride at a along flat ground but move more ills they climb hills . Then they might more quickly as they ( aim down hills . they may stop to fix their bikes . at cyclist does not have speed , the cyclist does have an average speed throughout a race . To late average speed ii ) divide the ( mil distance traveled ( by the total time ( I ) For example . suppose a cyclist travels 52 kilometers during the first . Then the cyclist travels I kilometers during the next hour . The speed of the cyclist ix the total divided by the total time . total distance ( 32 13 45 ( Average ( 15 The cyclist average speed is 15 per hour . can write the formula for speed I ! on . Su , if you know any two of these quantities . you can calculate the third . Instantaneous Speed Calculating , the speed at at cyclist during race is . it is also useful to the . Instantaneous speed is the rate at which an is moving at at given instant in time . How do you average speed ?

Measuring Spud Cyclists use an electronic device known as a cyclometer to track their speed over the course of their travel A cyclometer can calculate both average and instantaneous speed . Comparing and Contrasting why the Instantaneous speed and the average speed shown below are different .

Velocity Suppose you hear that at is trawling at a speed of 25 . Should you prepare for the storm ?

That depends on the direction of the storm motion . Velocity ( is speed in a given direction . Like ment . velocity is a vector . it has hath a magnitude ( and ! direction . For example , the velocity of at storm can he described as moving to the east . As with all vectors , the magnitude and direction of velocity are shown by the length and the direction of an arrow . Like speed . velocity may change over time . in velocity may be due to changes in speed . changes in direction . or both . Thus . if the storm continued to move at the same speed but changed tion . this would be change in its velocity . Video Id Tri ) i School Motion Tech Design in History The Speed of Transportation The speed with which people can travel from one place to another has increased over the years . 1885 Ben Tricycle Car Introduced This was the first internal combustion ( immobile sold to the public . Although It is an ancestor the modern automobile . its top speed was onry about 15 not much faster than a

In some situations . describing the velocity of moving objects can be very important . For example . air traffic controllers must keep Close track of the velocities of the aircraft under their . These continually change as airplanes head and on lhe . An error in determining at velocity . either in speed or in direction . could lead to a collision . Velocity is also important to airplane pilots . For example , stunt pilots make spectacular use of their control over the velocity oftheir . To avoid colliding with other aircraft , these skilled pilots must have precise control of both their writing In speed and direction . Stunt pilots use this control to stay in close formation while flying ul at high speed . styles of automobile were ?

Were sedans , convertibles . station wagons , or sports cars the bestsellers ?

Choose an era and automobiles of that time . Then write an advertisement lot one particular style of car . Be sure to include information from your research . 1934 Zephyr The first passenger train In the United States was the . The Zephyr set a record . traveling from Denver to Chicago at in . I average speed of more than Inn . 2003 Maglev In Motion The first commercial application of maglev ( magnetic ) was unveiled in Shanghai , China . During the trip from International Airport to district , the min operates at I top speed of 430 . reducing commuting time from 45 minutes to lust . 9345

Motion on Da . Morton Visit Web Code ( 3011 Graphing Motion You ( an use graphs to interpret . On the jogger first day of training , her speed is the same at every point . On the second day of training . her speed varies . Reading Graphs On the first day , how far does the jogger run in minutes ?

3460 ( 1200 ) 200 Graphing Speed You can show the motion ofan object on a line graph in which you plot distance versus time . The graphs you we in Figure are ' ime graphs . Time is shown on the axis , or . Distance , or position , is shown on the vertical axis . or . A point on the line represents the an object has traveled from the origin or ii reference point at a particular time . The point is time . and the is distance . The steepness of at line on a graph is called slope . The slope tells you how fast one variable changes in relation to the other variable in the graph . In other words . slope tells you the rate of change . slope of at graph represents speed . that is , the rate that distance changes in relation to time . The steeper the slope is . the greater the speed . A constant slope represents motion at constant speed , Calculating Slope You am calculate the slope of at line by dividing the rise by the run . The rise is the vertical between any two points on the line . The run is the horizontal difference between the same two points . slope Run in Figure , using the points shown , the rise is 400 meters and the run is minutes . To the slope . you divide 400 meters by minutes . The slope is per minute .

Motion moo Segment Slope I 200 st 300 Run min 600 . no ' Segment Slope 200 Different Slopes Most do not travel at a constant speed . The graph above shows a motion on her second day . The line is divided into three segments . The slope ul each segment is different . From the steepness of the you can tell that the jogger mu the during the third segment , The ( line in the second segment shows that the distance did not change at all . Reading . Writing Target Reading Skill Identify Main tum the lirst two paragraphs under Speed on page 342 . Draw graphic the main idea and supporting details . The sentence is the main idea . Reviewing Key Concepts . Identifying What does the slope of a ' graph show you about the motion of an graph is 600 and the run is minutes . What is the slope of the line ?

Calculating The rise of at line on it dist ut ( velocity is constant ?

is ?

in . Calculating What is speed ( car that travels in ?

mug . Calculating If you walked at an Think about I recent that Lil speed of . how long would take to you have . What was the approximate ( at road that is wide ?

total distance and a . Defining What is velocity ?

time It took ?

calculate your average speed I ) Describing Describe the two ways in which from this . how ELI velocity can change . your spud varied over the . Applying Concepts Your car speedometer 000 reads a ( 35 . Can say Inclined to Roll Problem How does the steepness of a ramp affect how fast an object rolling off it moves across the floor ?

Skills Focus measuring , calculating , graphing Materials skateboard I meter stick protractor masking tape flat board , about long small piece of sturdy cardboard supports to prop up the board ( books . boxes ) two stopwatches Procedure . In your notebook , make a data table like the one below . space for five angles . Lay the board on the floor . Using ing tape , mark a starting line in the middle of the board . Mark a finish line on the floor beyond one end of the board . Place a barrier after the finish line . Data Table ( Go ' Prop up the other end of the board to make a slight incline . Use a protractor to measure the angle that the board makes with the ground . Record the angle in your data table . Working in groups of three , have one person hold the skateboard so that its front wheels are even with the starting line . As the holder releases the skateboard , the other two dents should start their stopwatches . One timer should stop his or her stopwatch when the front wheels of the skateboard reach the end of the incline . For Data sharing Visit ( Web ( ode . The second timer should stop his or her watch when the front wheels reach the ish line . Record the times in your data table in the columns labeled Time I and Time , Repeat Steps two more times . if your results for the three times are within second of one another , carry out more trials . lE ) degrees ) Number ( Time Time Time ( Ii ( I )

. Repeat Steps four more times , making the ramp gradually steeper each time . For each angle of the incline , complete the following calculations and record them in your data table . a . Find the average time the skateboard takes to get to the bottom of the ramp ( Time ) Find the average time the skateboard takes to get to the finish line ( Time ) Subtract the average of Time from the average of Time . Analyze and conclude . Calculating How can you find the average speed of the skateboard across the floor for each angle of the incline ?

Determine the average speed for each angle and record it in your data table . Classifying Which is your manipulated able and which is your responding variable in this experiment ?

Explain . For a discussion of manipulated and responding variables , see the Skills Handbook . Graphing On a graph , plot the average speed 01 the skateboard ( on the ) against the angle of the ramp ( on the ) Drawing Conclusions what does your graph show about the relationship between the skateboards speed and the angle of the ramp ! Measuring your measurements for , time , or angle were inaccurate , how would your results have been affected ?

Communicating Do you think your method of timing was accurate ?

Did the timers start and stop their stopwatches exactly at the appropriate points ?

How could the accuracy of the timing be improved ?

Write a brief procedure for your method . Design an Experiment A truck driver transporting new cars needs to roll the cars off the truck . You offer to design a ramp to help with the task . What measurements would you make that might be useful ?

Design an experiment to test your ideas . Obtain your teacher permission before carrying out your investigation .

Section Students know changes in velocity may be due to in speed , direction , or both ! Students know nowto graphs oi versus time and graphs of speed versus time for motion in a single direction . What kind of motion does acceleration refer to ?

How do you calculate acceleration ?

What graph can be used to the motion of an accelerating object ?

Key Term acceleration 350 Integrating Mathematics Acceleration Will You Hurry Up ?

Measure 10 meters in an open area . Mark the distance with masking tape . walk the 10 meters in such a way that you keep moving taster throughout the entire distance . Have a partner time you . Repeat Step , walking the 10 meters in less time than you did before . Then try it again , this time walking the distance in twice the time as the first . Remember to keep speeding on throughout the entire 10 meters . Think it Over inferring How is the change in your speed related to the time in which you walk the course ?

The throws . The ball , this butter . 00 ' the hal it goes . It going . going , gone ! A home run ! landing , the ball went through changes in motion . It sped up in the pitcher hand . and lost speed as it traveled . Tho ball stopped when it hit the bat . changed . tip again . and slowed down . of motion similar . Changing Velocity Suppose you are passenger in car stopped at a red light . When the light changes to . the driver steps on the . As result . the cur up . or accelerates . In . tha process of Acceleration has a more in science . enlists acceleration as the rate at which velocity with time . Recall that velocity describes both the speed and direction of an . A in velocity can ' a change in either speed or both . In science , acceleration refers to increasing speed , decreasing speed , or changing direction . and . tion is at with El magnitude and a direction .

A A aha A softball when direction when thrown . hi ! A softball when it is caught . A . Increasing Speed an . when the throws it . and but ii . A mi that begin to a stopped ii oi up In ( i ( mu . Fur , yuu ( tidal down ai 1111 on your bike . Decreasing Speed lust as can speed up . they can also low down . This in speed is called . iu ' ir . when it in mill . A car when it stops ! red light . Changing Direction ti ' slant um . i in ( Ar ax il gum in tho mid . i . il iLs ) i the , when il ( il ' i ' in ' ing speed . is ( or ) along i circular path . For ' the walk why i ' they in . Reading How can a car he accelerating if its speed is constant al 65 I FIGURE Ai i A accelerates when it is thrown , taught , or What ( in motion occurs In eath example ?

Chapter 351 Analyzing Acceleration The velocity ofthe airplane above increases by the same amount each second . Interpreting Diagrams How does the distance traveled change in each second ?

GE For . Links an acceleration Visit Web Code sort ! 3510 Calculating Acceleration Acceleration describes the rate at which velocity changes . Like velocity , acceleration is a vector . it has both a magnitude and a direction . If an object is not changing direction . you can describe its acceleration as the rate at which its speed changes . To determine the acceleration of an object . you must calculate it change in velocity per unit of time . This is by the following formula . Final vel Time If velocity is measured in meters per second ) and time is measured in seconds . the Si unit of acceleration is meters per second per second , or . Suppose velocity is measured in kilometers per hour and time is measured in hours . Then the unit for acceleration is kilometers per hour per hour , or . To understand acceleration , imagine a small airplane mov ing down a runway in a straight line . Figure shows the plane morion alter each of the seconds of its acceleration . To calculate the acceleration of the airplane , you must first subtract the initial velocity of from the velocity of 40 Then divide the change in velocity by the time , seconds . Acceleration Acceleration I The airplane accelerates to the right at a rate of . This means that the velocity increases by every ond . Notice in Figure that , after each second oi travel , the plane velocity is greater than it was the previous second . iii ) its acceleration ?

Mimi Algebra Sample Calculating Acceleration As a roller coaster car starts down a slope , its velocity is . But seconds later , its velocity is 22 in the same direction . What is its acceleration ?

a Read and Understand information are you Initial velocity Final velocity 22 Time I Plan and Solve quantity are you trying to calculate ?

The acceleration of the roller coaster car I what formula contains the given quantities and the unknown quantity ?

Final velocity initial Acceleration Time Perform the calculation . Acceleration ?

calculating Acceleration A 18 I falling accelerates Acceleration from lo to 30 in seconds . What is the raindrop acceleration ?

The acceleration is dawn the slope . A certain car can accelerate from Bad rest to 27 in seconds . nu ' Find the car acceleration . The answer is reasonable . if the car velocity increases by each second , its velocity will be 10 after second , 16 after seconds . and 22 after seconds 0353

Speed lime ' Graph The slanted , straight line on this graph tells you that the cyclist is accelerating at a constant rate The slope of a graph tells you the object acceleration . Predicting How would the slope of the graph change if the cyclist were accelerating at a greater rate ?

At a lesser rate ?

354 Graphing Acceleration Suppose you ride your bicycle down a long , steep hill . At the top of the hill yuur speed is . As you start clown the hill . your speed ' second , you at at speed and travel a greater than the . During the live seconds it takes you to reach the bottom of the hill . you are an ( You can use both I graph and it graph to analyze the motion of an accelerating object . Graph Figure shows a time graph for your bicycle ride down the hill , What can you learn by this graph ?

Since linc slants upward . the graph shows that your speed was increasing . Next . since the lint is straight , you cant tell that your acceleration was constant . A slanted . straight line on a graph means that the object is accelerating at a constant rate . This is an example ola linear graph . In a linear graph . the ( data a straight line . A horizontal line on a graph means that the object is moving at a constant speed . The slope of a line on graph tion . To calculate the slope . choose any two points on the line . Then . divide the rise by the run . You down the hill at a constant rule of .

Graph You am also Show the motion of an accelerating object with a ' graph . Figure shows a time graph for your bike ride . On this type , a curved line means that the object is accelerating . The graph shown in Figure ?

is nonlinear . In a nonlinear graph . the data form a curved line when plotted . The curved line in Figure ) tells you that during each second , you traveled a greater than the second before . For example , you traveled a greater during the third second than you did during the first second . The curved line in Figure also tells you that ing each second your speed is greater than the second before . Recall that the slope of a graph is the speed of an object . Front second to second . the slope of the in Figure gets sleeper and The curved line on this steeper . Since the slope is increasing . you can conclude ' that the speed is also increasing . You are accelerating . balm What does a curved line on I graph tell you ?

a section Assessment it i ' target Reading Skill Identify Main Ideas Naming What types ut ' can you use the text under Velocity on pages to analyze the acceleration of an object ?

Draw a graphic organizer for this topic . I ) Describing Describe the motion ofan Us the sentence as the main idea . whim if its staph is Ke ' um i I Predicting What would a I . at way ' an time graph look like for the i can accelerate ?

Summarizing Describe how a baseball player accelerates as he runs around the in part ( bases after hitting it home run . Applying Concepts An ice skater glides ( In around a at a constant speed ul . Is the skater accelerating ?

Explain your answer . A A i ! Identifying What formula do you use to ' Of Will calculate the acceleration of an object ! 95 Om ' moving iu a straight line ?

seconds . What is her acceleration ?

Calculating The velocity of a cyclist moving . Calculating Acceleration What is a race in a straight line changes from rule to car acceleration if its velocity changes IS in It ) What is the cyclist from to 40 in seconds ?

acceleration ?

Stopping on a Dime Problem The school will put in a new basketball court in a small area between two buildings . Safety is an important consideration in the design of the court . What is the distance needed between an line and a wall so that a player can stop before hitting the wall ?

Skills Focus calculating . interpreting data Materials wooden meter stick tape measure stopwatches or watches with second hands Procedure PAR ! Reaction Time . Have your partner suspend a wooden meter stick , zero end down , between your thumb and index linger , as shown . Your thumb and index finger should be about apart . Reaction Time Distance Tine Distance ) 15 17 18 19 20 21 23 24 356 . Your partner will drop the meter stick out giving you any warning . Try to grab it with your thumb and index finger . Note the level at which you grabbed the meter stick and use the chart shown to deter mine your reaction time . Record the time in the class data table . Reverse roles with your partner and repeat Steps . Stopping Distance . On the school field or in the gymnasium , mark a distance of 25 Be sure to remove any obstacles from the ( DUNE . Have your partner time how long it takes you to run the course at full speed . After you pass the mark , come to a stop as quickly as possible and remain standing . Vou must not slow down before the mark . Have your partner measure the distance from the mark to your position . This is the distance you need to come to A complete stop . and distance into the class data table . Reverse roles with your partner . Enter your partner time and distance into the class data table .

Class Data Table Student . Name Time Running Time Distance ( Analyze and conclude I . Calculate the average speed of the student who ran the course the fastest . Interpreting Data the speed of the fastest student ( calculated in Question ) by the slowest reaction time listed in the class data table . Why would you be interested in this product ?

Interpreting Data Add the distance lated in Question to the longest stopping distance in the class data table . What does this total distance represent ?

Drawing Conclusions Explain why it is important to use the fastest speed , the slowest reaction time , and the longest stopping distance in your calculations . Controlling Variables What other factors should you take into amount to get results that apply to a real basketball court ?

Communicating Suppose you calculate that the distance from the line to the wall of the basketball court is too short for safety . Write a proposal to the school that describes the problem . In your proposal , suggest a strategy for making the court safer . More to Explore Visit a local playground and examine it from the viewpoint of safety , Use what you learned about stopping distance as one of your guidelines , but also try to identify other potentially unsafe . Write a letter to the Department oi Parks or to the officials of your town informing them of your findings .

Standards Focus Framework Students should begin to grasp tour concepts that help to unify and energy the laws at conservation , What factors affect an kinetic energy and potential energy ?

Now can energy and potential energy be what is the law oi conservation ot energy ?

Key terms I work I energy I energy I potential energy I potential energy ' potential energy ' mechanical energy I law of conservation of energy when a breeze doe lifting team . it transfers energy to them . 35 ! How High Does a Ball Bounce ?

Hold a meter stick vertically , with the zero end on the ground . Drop a tennis ball from 50 . Record the height to which it bounces . Drop the tennis ball from the 100 mark and record the height to which it bounces . Predict how high the ball will bounce it dropped from the mark . Test your prediction , Think it Over Observing How does the height from which you drop the ball relate to the height to which the ball bounces ?

When blows a leaf through the air . it causes a change . this change is in the position scientist would the wind as doing work nit the lull . is done when an object is caused to mutt it certain . The ability to do work or is called energy . So . the has energy . an lIl or living thing docs work on object . wine uf its is transform ! to that . You can think at work . as dis transfer . When is ' the upon which work is done gains energy . Thu SI unit for work and energy is .

Kinetic Energy A moving as the wind , can do work when it strikes another object and moves it some distance . Because the ing object does work . it has energy The energy an object has due to its motion is called kinetic energy , The word kinetic comes from the Greek word , which means nuns and its speed . Kinetic energy increases as mass increases . For example . the left lane in Figure shows at bowling ball and a golf ball rolling down a bowling lane at the same speed . The bowling ball has more miss . so you must use more energy to roll it . The bowling brill is more likely to knock down the pins because it has more kinetic energy than the golf ball . Kinetic energy also increases when speed increases . For example . suppose you have two identical bowling balls and you roll one ball so it moves at a greater speed than the other . You must throw the ball harder to give it the greater speed . In other words . you transfer more energy to it . Therefore , the faster ball has more kinetic energy . There is a mathematical relationship between kinetic energy . mass , and spud . Note that changing the speed of an object will have a greater effect on its kinetic energy than changing its mass by the same factor . This is because speed is squared in the kinetic energy equation . For instance . doubling the mass of an object will double its kinetic energy . But doubling its speed will quadruple its kinetic energy . What is kinetic energy ?

Less mus means less kinetic energy . Greater mass means greater kinetic energy . Less speed means less kinetic energy . Exponent An exponent tells how many times a number is used as a factor . For example . can be written as . Von read this number as three In the formula for kinetic energy , speed is squared . For example , you can calculate the kinetic energy of a person moving at a speed of using the below . KE Mass ) 140 . in or Note ' Practice Problem What is the kinetic energy of a rock moving at a speed of 10 Flaunt Io Kinetic Energy Kinetic energy increases as mass and speed increase . In each example , which object will transfer more energy to the pins ?

Why ?

Greater speed means greater kinetic energy . 39 11 The blue skier has more gravitational potential energy because he is at a greater height . Gravitational Potential Energy Gravitational potential energy increases as weight and height . Interpreting Diagram Does the red skier have more gravitational potential energy on the higher ski jump or the lower one ?

Why ?

For links on energy Visit Web ( ode 3600 The green skier has more gravitational potential energy because he weighs Potential Energy Some objects have stored energy as a result of their positions or shapes . When you lift a book up from the floor or compress a spring . you transfer energy to it . The energy is stored . it might be used later when the book fails to the or the spring is released . Stored energy that results from the position or shape of an object is called potential energy . This type of energy has the potential to do work . Gravitational Potential Energy Potential related to an object height is called potential energy . An object gravitational potential energy depends on its weight and on its height relative to a reference point . Gravitational potential energy I Weight Height For example , the skier on the left in Figure It weighs 500 . if the ski jump is 40 meters high . the skier has 500 newtons 40 meters , or I , of gravitational energy . A skier has more gravitational potential energy on a high ski jump than on a low one . The more an obiect weighs , or the greater its height . the greater its gravitational potential energy . At the same height . a skier has more gravitational potential energy than a skier . Elastic Potential Energy An object gains a different type of potential energy when it is stretched or squeezed . The potential energy of objects that can be stretched or compressed is called elastic potential energy . For example . an archer pulling back on an arrow changes the shape of the bow . The how new has that can be used to send the arrow flying to its target .

Energy Transformation and Conservation Look at Figure 12 . The quarterback transfers energy to the football as he throws it In the receiver . As the hall sails through ' the air , it has energy because it is moving . The ball ' also has potential energy because of its position above the ground . An object combined kinetic energy and potential energy is called mechanical energy . You can find an object mechanical energy by adding the object kinetic energy and potential energy . Go Online energy Kinetic energy Potential energy You can use this to fund the mechanical energy of the football in Figure 12 . Suppose football has a weight of and a mass of . If the football is at of . it has a kinetic energy of ( 14 39 I . If the football is meters above the ground , I it has it gravitational potential energy of 12 I due Mechanical Energy to its position . The total mechanical energy of the football at ' kinetic that point I joules Why what two loans at energy combine to make dim The he ' energy ?

energy ?

Mechanical energy 39 12 51 Gravitational potential energy a 12 Kinetic energy 391 Fun 13 The kinetic energy of an orange thrown into the air becomes gravitational potential energy . its potential energy becomes kinetic energy as it falls . I , Go Between Potential and Kinetic Energy One of the most common energy transformations is the transformation between potential energy and kinetic . waterfalls such as Yosemite Falls , potential energy is transformed to kinetic energy . The water at the top of the falls has gravitational potential energy . As the water plunges . its speed increases . Its potential energy becomes kinetic energy . Any object that rise or falls experiences I in its kinetic and gravitational potential energy . Look at the orange in Figure 13 . When it moves . the orange has kinetic energy . As it rises . it slows down . Its potential energy increases as its kinetic energy decreases . At the highest point in its path . the orange stops moving for an instant . Since there is no motion . the orange no longer has kinetic energy . But it has potential energy . As the orange falls . kinetic energy while potential energy decreases . in a pendulum , a continuous between kinetic and potential energy takes place . At the highest point in its swing . the pendulum in Figure 14 comes to a stop . so it has only gravitational potential . As the pendulum swings downward , it speeds up . Its potential energy is formed to kinetic energy . The pendulum is at its greatest speed at the bottom of its swing . There . all its energy is kinetic energy . As the pendulum swings to the other side . its height increases . The pendulum regains gravitational potential energy and loses kinetic energy . Al the top of its swing , it comes to a stop again . The pattern continues . For Energy activity I Web Code ) mun Pendulum A pendulum continuously potential energy and back . two points the pendulum potential energy greatest ?

transforms energy from kinetic to Interpreting Diagrams At what Greatest potential energy . no kinetic energy Greatest potential energy , no kinetic energy Greatest kinetic energy . no potential energy 3610 Vocabulary Skill A ( Words Conservation of Energy If you sat il spinning top in motion , will the top remain in motion ?

No . it will not . Then what to its ?

In tho ?

Again , the in no . The law of of energy status that when out form of is to another , no energy is destroyed in the process . According to the law of conservation of energy , energy ( am not be created or destroyed . So the total amount of is the ' after any . lfyou add up all the new forms of energy after . all of the original will for . So what . to the energy ol the top in Figure IS ?

As the top spins . il rubs against and air resistance . As a result . some of its kinetic is into energy . 50 , the of the spinning top is to thermal . The top slows and falls on its side , but its is not is transformed . What causes a top to stop spinning ?

Section . is the it the word in the ! energy ?

Reviewing Kay Concepts Identifying What is kinetic ?

what unit is it ?

Explaining ( kinetic energy ?

Calculating A ) car is moving at speed of 10 IS thi cat ?

Identifying What is potential ?

Explaining What an gravitational energy ?

What is the potential energy of a ! when she is in the ground ?

565 Assessment Flaunt 15 Conservation of Energy A spinning top kinetic energy I ! not It is into thermal energy through friction . Applying Concepts How much of the top kinetic energy thermal energy ?

Framework . Reading Summarizing State of I in your own . la , Describing Describe this that occur when you bounce it hall . Applying Concepts a hall had a potential energy I when you dropped it . he its kinetic ! tail hit the ?

Ignore the El Practice . Exponents What is the kinetic energy of a ball moving at ?

Exponent How would the kinetic energy of the bail in Question change if its mass were doubled ?

If its speed were doubled ?

363 Chapter . Study Guide an the at an by in position , speed . direction . and . Describing Motion ( Key Concepts I IS in motion it In a point . is the mini ! between rwo palms . is the length and direction ofa linc starring and ending . Key Terms di . paint vector ' Speed and velocity ( Key Contents . 31 . To ( the obi . di the travels by the time IY ta kes travel ( li . Time Changes in Iu hungry in ( in . limit . The dope of di graph ( is , me in to , Run Key Terms speed ze ) lAu speed ' Acceleration Key ! In sci . refers lu . ur di . Tu ( in ! unit of lime . Final ' velocity Time ' You um uw bath graph and graph to of an . Key Term ' Energy Key Framework The energy of an on and its . Energy Mass . An ui ) energy on and on its ' In nu . I ( energy Mech ital energy Kinetic energy whim that ( I ( 11 ( hang in its and ' In Ihr Law , or Key Terms work clam kinetic energy energy ' law 111 . 111 ui

Review and Assessment . i For . Visit ( um Web Code Target Reading Potential Energy Skill Identifying Main Ideas the first paragraph . Then 507113 NOV ?

the Wed graphic . Reviewing Key Choose the letter of the best answer . Complete the following sentences so that mu ?

A change in position with ' i the ' Displacement is min . Both velocity and are vectors HINT . motion . I ' es . It travels 30 Ill 20 minutes , HINT HINT ' can its ( An ! at I ' INT av , speed is acceleration direction , 10 . Thu law of conservation of energy miles that my HINT . You do nut know an ' until you know its . ing in . News Two trucks have competed In I . The rate at which ) is a , an rude the ' i and who won . Explain the role the average ' speed of the trucks played . Tell how avenge ( speed can be calculated . di , nu ! The energy that an has due to in . motion is called energy . elastic potential energy . energy . Motion 365

Review and Assessment Concepts 11 . A the rear ut ) her motion as seen from reference point on the train . Then it ( run reference on the ground . Which has greater , that ( son in 60 or a duck that 60 II ! in seconds ?

Explain . 13 . insect int that is put Into with the disc . the . ur nut ?

14 . eagle from its perch in it UK to the . Describe energy . Inferring How can you tell object is when its ' is 00 slow In see ?

king cally 16 . Interpreting Graphs The graph below shows the car . the ear average speed over the time intervals . the entire time . During interval is the cur the ?

Th ?

17 . Applying concepts A family takes cur trip . They an hour at 80 and then for hours at ill . Find speed during the trip . 18 . Problem Solving A ' girl walks ( it flight ul ' stairs su that she is in her starting level . What is the change In the gills gravitational energy ?

3650 Math Practice 19 . Calculating Acceleration During a shirt , hockey puck takes to accelerate In 35 . is the acceleration ) 10 . Exponent What ?

21 . Exponents What is the kinetic ( Il ?

Applying Skills Use the illustration of the motion of a ladybug to answer Questions . Start Finish 22 . Measuring Measure the from the and lrom line it to the line . Measure the tenth meter . 13 . Calculating Starting at real . the accelerated to line and then at speed until it the line . If the ladybug took 15 seconds to from In the line , its speed during that time . 14 . Interpreting Data The speed you in Question also the speed the ladybug had at the end of at line it . fur the ladybug to the start line line . is its during that time ?

Stand ' Performance Assessment ( your display card so that easy to . to put title on each card stating the speed that you . Place the cards in order from the speed In the Then . them . Compare your Ic with those students .

Standards Practice Choose the letter of the best answer . Suppose you moved meters forward and then meters backward . What is your displacement from your original position ?

A forward I in forward I I backward 24 backward . Your father is driving to the beach . He drives at one speed for two hours . He drives at at different speed for another two hours and a third speed or the tinal hour . How would you find his average speed for all hours ?

A Divide total time by total distance . I Multiply total time by total distance . Divide total distance by total time . Subtract total time from total distance . A car travels in a constant speed ol ' for hours . What is the total distance that the car traveled ?

A 20 63 . Use the graph below to answer Question . Speed lime i ! According to the graph of at cyclist motion above . the cyclist is A moving at a constant speed . I accelerating at a constant rate . slowing down at constant rate . moving It constant distance per second . Success it Tracker Orin at . Which of the following is NOT a vector ?

A displacement speed velocity acceleration No objects traveling at the same speed have different velocities if they A start at times . I ! travel different distances . have different masses . move in directions . Use the graph below to answer Question . Distance Time for a Runner . I . The graph shows distance versus time for a moving at a speed . What is the runner speed ?

A I 00 I 200 400 ( idea Write a paragraph that describes the similarities and among speed . velocity , and acceleration . 0357