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# MECHANICS PHYS 218

Texas A&M

GPA 3.73

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This 193 page Class Notes was uploaded by Alba Ankunding on Wednesday October 21, 2015. The Class Notes belongs to PHYS 218 at Texas A&M University taught by David Toback in Fall. Since its upload, it has received 72 views. For similar materials see /class/225903/phys-218-texas-a-m-university in Physics 2 at Texas A&M University.

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Date Created: 10/21/15

Physics 218 Lecture 17 Dr39 David Toback Checklist for Today Things that were due Monday Chapter 8 Quizzes on WebCT Things due Tuesday Read Chapters 10 amp 11 Thin s that are due yesterday for Reci ation Chapter 9 problems Things due Monday Chapter 9 in WebCT Physics 218 Lecture XVII 2 The Schedule This Week 317 Chapter 8 quizzes due in WebCT Reading for Chapters 10 amp 11 Lecture on Chapter 10 11 in recitation next week Chapter 9 and Exam 2 Review in recitation Next Week 324 Chapter 9 due in WebCT minipractice exam 2 available Exam 2 on Tuesday Recitation on Chapters 10 amp 11 Reading for Chapters 12 amp 13 for Thursday Lecture 12 amp 13 on Thursday Following week Chapter 10 amp 11 material in WebCT Reading Chapters 1416 Lectures on 1416 Lectures 1 and 2 of Four Recitation on Chapters 12 amp 13 Today39s Lecture Rest of Chap 10 Center of Mass Center of Mass and Translational Motion Collision amp Explosion Problems using Conservation of Momentum Center of Mass Physics 218 Lecture XVII 4 Cem er of Mass CM What is The C39em er of Mass More impor39l39arrl39ly quotWhy do we care This is a special pain in space where quotifis as if fhe objecf could be replaced by all fhe mass af fhaf one liffe poim Physics 218 Lecture XVII 6 CenTer of Mass CM ConT Examples where This is useful 39 We have a spherical cow ThaT weighs Two Tons We can model defenesTraTing her as if she were a Slhge poi1f We can model The earTh moving around The sun as a single poinT aT quotThe cen fer of The earfh AT some level we ve been assuming These Things for doing problems all semesTer Physics 218 LecTure XVII 7 Center of Mass CM Cont Yet another example there are only a couple of points on a ruler That you can put your finger under and hold it up Your finger provides the normal force Physics 218 Lecture XVII 8 Visual Examples 1i Trajectory as a point since both have The same acceleration and initial velocity I HYSICS 16 LCCTLIF39C AVLJ y How do you calculate CM 1 Pick an origin 2 Look at each piece of massquot and figure out how much mass it has m how far it is vector displacement from the origin Take mass times position 3 Add them all up and divide out by the sum of the masses The center of mass is a displacement vector quotreafgve f0 someI origin hysics 218 Lecture XVI Spelling out The math my ma a m1 m2 2 cm for 2 parfices X quot1121 ma a mg m m2 m3 cm for 3 parfices efc No fe fhaf A7 is fhe 3 D vecfor a IZS39pacemmf Physics 218 Lecture XVII 11 2D Example Three balls with masses m1 m2 y and m3 are are m3 located 0139 The points given 1390 QM the right rCM Where 12539 fhe m1 P cem er of H1055 Physics 218 Lecture xvn 12 quot12 x 0 wmf 2 ways 1390 s0ve collisionexplosion problems 1 onserva39l39ion 01L 0 en139u in 0 At 1 direnc39l39ionn mSi m f 2W0139ching 139he Cen139er p12 of Mass Need 1390 be able 1390 d0 b0139h Pick easier me139h0d p l Physics is ne same Physics 218 Lecture XVII 13 Two balls in ouTer space Two balls are moving in ouTer space They have known mosses 2M and 3M and speeds 41 and 2V respecTively and They collide oT The origin The direcTions are as shown in The figure AfTer The collision The Two bolls sTick TogeTher and form a blob Whaf 13 The final velocify of The blob y Speed 4v 39 i nore roviT X 9 9 Y peed 2v Physics 218 LecTure XVII 14 Toy Rocket Problem Your friend fires a toy rocket into the air with an unknown velocity You observe that at the peak of its trajectory it has traveled a distance a in the x direction It then breaks into two equal mass pieces Part I falls straight down with no initial velocity Where does re 2 quot half of re fay em w Two Balls in Two Dimensions Before a collision ball 1 moves with y speed V1 in the x 1 direction while ball I x 2 is at rest Both v 6 have the some mass 1gt neg L After the collision the balls 90 off at angles and 0 f What are the velocities V 1 and V z after the collision Physics 218 Lecture XVII 16 Coming up next week Homework 9 due Monday in WebCT Make sure you do ALL the quizzes in the learning module folder Minipractice exam 2 and bonus points Exam 2 Tuesday March 25quot Start Chapters 1216 in Lecture on Thursday Physics 218 Lecture XVII 17 Physics 218 Lecture 25 Dr39 David Toback Checklist for Today Things due earlier This week Chap rer 15 amp 16 in WebCT Chap rer 18 reading Chap rer 18 problems as Recitation Prep Today LAST LECTURE Things due Monday Chap rer 18 in WebCT Physics 218 Lecture XXV 2 The Schedule This Week 421 Monday Chapter 15 amp 16 due in WebCT Tues Reading amp Lecture Chapter 18 Wed Recitation on Chapter 18 Lab Thurs Last lecture Chapter 18 Not covering Chapter 19 Next Week 428 No lectures or recitations Chapter 18 HW due in WebCT Exam le final problems at http acultyphysicstarnuedutoback218LecturesFinalReviewpdf Week after that 55 Final Monday May 5 1PM3PM in this room NexT SemesTer Some of you conTinue To ask abouT nexT semesTer I am NOT Teaching 208 However I am planning on Teaching a new course 31y Bang Black Holes No Mafh InTro To Cosmology PHY5289 Based on quotA Brief Hsfory of Tittie by Tephen Hawking If you can39T Take iT you mighT pass This info along To friends Chap 13 Overview Oscillations Last time Oscillations and vibrations Equations of motion Our spherical cow Mass on a spring Simple Harmonic Motion This time Energy Physics 218 Lecture XXV 5 Review Simple Harmonic Motion erio Time it Takes 1390 get ack 1390 here rnyss nu LECYIII39E AAV o Questions Simple Harmonic Mo l39ion X A 5171a1139 Can you answer The following 39 WhaT 13 The ampI39Tude WhaT 13 The phase WhaT 13 The angular frequency WhaT 13 The velociTy aT The end pain Ts WhaT 13 The velociTy aT The middle Physics 218 Lecture XXV 9 Energy in SHO39s Potential Energy for a spring U 21k Kine39l39ic Energy for a block KE 21ml Total Energy E UE 21k 21mv3 Physics 218 Lecture XXV 10 Energy Example A box of mass m is attached to a spring of constant k stretched to a distance X0 held in place and then and released Ignore gravity and friction As a function of time I What is the position 2 What is the velocity 3 What is the kinetic energy 4 What is the potential energy 5 What is the total energy of the system Physics 218 Lecture XXV 11 Mass on a spring with gravity ake an un s rre rched spring Gen rly add a mass and Ie r go The ro ral s rre rch from equilibrium is a distance h before if s rar rs ro rise again If Then oscilla res Whaf 12539 fhe angular velocify a7 of maran hI Physics 218 Lecture XXV Challenge Exam Announcement of this semester39s 218 Challenge Exam Monday April 28 at 600PM Not required just for fun Does not will not count as part of your final grade Test your skills against the best Aggies from all the Physics 218 sections not just this lecture on Physics 218 material Students who perform well will be recognized as Mechanics Schoars and honored at a banquet in their honor Other prizes including cash Handout information on my Webite Physics 218 Lecture XXV 13 That39s it Nexf Week No classes or Reci ra rions HW for Chapter 18 due Final Monday May 5 1PM3PM in This room Chap rer39s 14 16 and 18 will be on The final I guaranfee a problem from each Good luck studying for Finals Physics 218 Lecture XXV 14 Physics 218 Lecture 19 Dr39 David Toback Checklist for Today Things due Last Thursday Read Chapters 12 amp 13 Things that were due Monday Chapter 10 amp 11 HW on WebCT Things that are due tomorrow for Recitation Chapter 12amp13 problems Read Lab hand out on webpage Things due next Monday Chapter 12 amp 13 in WebCT Physics 218 Lecture XIX 2 The Schedule This Week 331 Mon Chapter 10 amp 11 due material in WebCT Tues Second lecture on Chaps 12 amp 13 Wed Recitation on Chapters 12 amp 13 Lab Reading for Thurs Chapters 1416 Thurs Lecture Chap 14 Next week 47 Mon Chapter 12 amp 13 material due in WebCT Tues Second Lecture on Chap 14 Wed Recitation on Chap 14 Lab Thurs Lecture Chap 15 Part 1 Week after that 4 14 Monday Chapter 14 due in WebCT Tues Exam 3 Chaps 1013 Wed Recitation on Chap 15 Lab Thurs Lecture on Chap 15 Part 2 Overview Chapters 1216 are about Rotational Motion While we39ll do Exam 3 on Chapters 10 13 we39ll do the lectures on 1216 in six combined lectures Give extra time after the lectures to Study for the exam The book does the math I39ll focus on the understanding and making the issues more intuitive Physics 218 Lecture XIX 4 Overview Rotational Motion Take our results from linear physics and do the same for angular physics Analogue of Position lt Velocity lt Acceleration lt Force Mass Momentum Energy Physics 218 Lecture XIX 6 Rotation and Translation Physics 218 Lecture XIX 7 Rolling without Slipping In reality cor39 39l39ir39es bo39l39h rotate and 39l39r39onslo39l39e They are a good example of something which rolls Tronslo39l39es moves forward r39o39l39o39l39es wifhouf slipping Is fhere fric an Whaf kind Physics 218 Lecture XIX 8 Derivation The trick is to pick think of the wheel as sitting still and the ground moving past it with speed V Velocity of ground in bike frame DR Velocity of bike in ground frame wR Physics 218 Lecture XIX 9 Bicycle comes to Rest A bicycle with initial linear velocit V0 at f00 decelerates uniformly wit out slipping to rest over a distance a For a wheel of radius R a What 1339 The angular velocity at f00 b Total re vaufians before if stops 6 Tafa angular dZsfance fra verse by The wheel I i d The angular accelera flan quot All e The total Time unfi if stops as a 1T A lira1 a y H wuw A 2 5 3 cm H 3 Physics 218 Lecture XIX 10 Uniform Circular Motion Fancy words for moving in a circle with constant M We see this around us all the time Moon around the earth Earth around the sun Merrygorounds Constant a and Constant R Physics 218 Lecture XIX 11 Uniform Circular Motion Velocity 39 Velocity vector IVI tangent to the circle Z39s fhZS39 ball Physics 218 Lecture XIX 12 Centripetal Acceleration quotC39em er Seeking Acceleration vector VZR towards the cem er Acceleration is perpendicular to the velocity Physics 218 Circular MoTion GeT The speed Speed disTanceTime DisTance in 1 revoluTion divided by The Time iT Takes To go around V once No fe The fime fo go around once 12539 known as fhe Period or T Physics 218 LecTure XIX 14 Th Tri To Solvig Pblems M n 3 3 m T W Physics 218 Lecture XIX 15 Banking Angle You are a driver on The NASCAR cir39cui r Your car has mass m and is Traveling with a speed Varound a curve with Radius R Whaf angle 0 should fhe road be banked so fhaf no fricfion is required Lenquot xxx 16 Skidding on 0 Curve A COP Of mass m rounds a curve on a zed 17G mg mp 412 wuurv AM 17 Conical Pendulum A small ball of mass is suspended by a cord of length L and revolves in a circle with a radit 9 given by r LsnQ Whaf is 12 veoc I of 12 ball I 2 Calcuafe fhe pen gt lt7r4 of 12 ball 11 Enquot e N G Physics 218 Lecture XIX 18 Exam 2 Class average for The 2nd exam including The 5 poinTs was 65 Average for firsT Two exams is a 69 NoTe for sTudenTs who didn39T Take The minipracTice exam Exam 2 Average51 o High score75 Two exam average 60 almosT 20 poinTs below Those who Took iT Planning on only a small curve for now will decide afTer39 The 339quotd exam Physics 218 LecTure XIX 19 Should you Qdrop Many have asked quotshould I 4 drop Tolk To your advisor and read my FAQ Gener39ic advice Drop if you con39f keep up with The homework Qy yourself Physics 218 Lecture XIX 20 Next Time Wednesday Reci39l39a39l39ion Reci39l39a39l39ion on Chapters 12 amp 13 Wednesday Lab Elasfic Collisions Thur39sday Lecture on Chapter 14 Monday Chap39l39er39s 12 amp 13 due in WebCT Physics 218 Lecture XIX 21 Integrating WebBased Teaching Tools into Large University Physics Courses David Toback Department of Physics A M Teaching With Technology 2006 21 52006 1 Outline Overview Introductory Physics Multiple Course Goals and Challenges Our Online Math and Homework Quiz Systems Incorporating them into the course Results and Thoughts Teaching with Technology 2006 David Toback Texas AampM University 21520062 Overview Using webbased instruction in Introductory Physics courses is nothing new Studies show simply turning in homework online is no better than properly graded pen amp paper homework 39 What does appear to matter is the content and HOW online activities are structured This talk New tools How to incorporate them Teaching with Technology 2006 David Toback Texas AampM University 21520063 What is Physics 218 Large introductory course Ty ical enrollment is 1500 for Fal and 750 for Spring Split up into lecture sections 120 students lecture ingle professor per section Common syllabus instructor dependent lectures exams amp grades Teaching with Technology 2006 David Toback Texas AampM University 21520064 More on the course Course style is known in the literature as Traditional Lecture xZweek Recitation and lab XIweek Graduate student leader to solve problems Designed for firstyear Engineering maJors Preparation for engineering curriculum Calculus is a corequisite This is problematic more later Teaching with Technology 2006 David Toback Texas AampM University 21520065 Primary Goals Create Good PROBLEM SOLVERS Teaching with Technology 2006 David Toback Texas AampM University 21520066 What does this mean Being a good problem solverquot means many things to many different people Here I mean Understanding the concepts in the problem Turning the physical quantities into symbolic variables Translating the problem into the language of Mathematics symbolic notation Turning the crankquot on the math to find a Closed Formquot solution and a numerical solution Teaching with Technology 2006 David Toback Texas AampM University 2152006 7 A Silly Example Your car can drive at 60 mileshour How far can you Travel in 07 hours Speed 5 60 mihr39 Time 1 07 hours Tiger by Li mihr39 x 07 hr 42 mi Wan39r student To be able To do both Teaching with Technology 2006 David Toback Texas AampM University 21520068 The Teaching Challenges Many students have very poor math and problem solving skills Great variation between the best and the weakest students Most students aren39t taught to use variables High school quot ef good of plugging in five numbers in fa fhe egua ons we give youquot Teaching with Technology 2006 David Toback Texas AampM University 21520069 Other Challenges 39We have VERY limited human resources for grading feedback or tutoring time When this program began 2001 there were No webbased instruction or tools No math remediation materials Homework was not collected or graded No feedback other than exams and easy weekly recitation quizzes Teaching with Technology 2006 David Toback Texas AampM University 2152006 10 Yet more challenges Milny ldon39t know how to study at the college eve Often the smartest kid in their school didn39t have to spend too much time studying or do many problems Don39t know what to study I looked over the homework before the exam like I did in high school everything kinda made sensequot Don39t know how to tell if they39ve gotten the problem right Teaching with Technology 2006 David Toback Texas AampM University 2152006 11 Big Picture Solution Create Teaching while quizzingquot tools and deliver them with WebCT Two Separate Issues 1The Quiz Tools Themselves Nothing terribly new or complicated 2New vva s of incorporating them In 0 the course as a whole Design with both in mind Teaching with hnology 2006 David Toback Texas AampM University 2152006 12 SysTem Goals RemediaTe maTh deficiencies Level The playing field wiThouT biasing The grades in favor of The beTTerprepared AuTomaTe homework grading and provide quick feedback Guide sTudy Time Towards problem solving Teach sTudenTs how To check Their own work Make iT REALLY EASY for oTher insTrucTors To incorporaTe The Tools inTo Their courses Teaching wiTh Technology 2006 David Toback Texas AampM UniversiTy 2152006 13 Combine Elements of Good Teaching 39 Explicit Goals Immediate and Constant Feedback Balance between skilllevel and Challenge Improve timeontaskquot High expectations Motivation for performance The Opportunity to Repeat Until Masteryquot Teaching with Technology 2006 David Toback Texas AampM University 2152006 14 Overview of the Tools Three Separate Quizzing Tools 1 The Automated Mathematics Evaluation System AMES 2 The Computerized Homework Assignment Grading System CHAGS 3 Afterhomework QUizzes Intended to Consolidate Knowledge QUICK Teaching with Technology 2006 David Toback Texas AampM University 2152006 15 Why WebCT All tools implemented with WebCT but in principle could have used other formats Quiz tools readily available Design once reuse indefinitelyeasily for all instructors Students can use anywhere Class rosters automatically added Neo account security TA39s can enter in grades Huge server capacity We39re a HUGE hog of resources Great support from ITS Thanks Rhonda Teaching with Technology 2006 David Toback Texas AampM University 2152006 16 More on Theory We use some of the ideas in the non physics education literature in new ways Mastery Learning Repetition until achieving a certain score Precision Teaching Repetition until achieving a predetermined number of correct answers per unit time Teaching with Technology 2006 David Toback Texas AampM University 2152006 17 The Deal For ALL quizzes Passing requires a 100 score within the allotted time If they fail Indicate the correct answers Unlimited number of attempts without penalty Change the problem slightly on each attempt Passing required to move on to next quiz Required to pass all quizzes to pass the course Teaching with Technology 2006 David Toback Texas AampM University 2152006 18 NoTes Forcing 100 combaTs The TempTaTion To jusT do easy problems MulTiple Topics and difficulTy level incorporaTed inTo each quiz Encourages learning maTerial as a whole TudenTs moTivaTed by geTTing 100 for parT of Their grade NoTe Yes This means ThaT everyone geTs a 100 for Their homework grade All This does is shifT The mean grade in The coursequot TudenTs don39T undersTand This In pracTice Giving harder exams lower mean scores and making The homework only worTh abouT 15 of The grade Teaching wiTh Technology 2006 David Toback Texas AampM UniversiTy 2152006 19 The Sequence The sequencing of the quizzes is also important Course begins with the AMES math quizzes and they must get ten 100 o39s THEN the can move on to CHAGS Homework problems break the assignment into 3 parts When they get 100 on all three THEN they can move to QUICK for a homework 1 quiz When the finish that THEN they can move on t e Homework 2 etc Teaching with Technology 2006 David Toback Texas AampM University 2152006 20 More CarroTs The firsT inclass paperandpencil exam covers The Three ChapTer39s of The TexT book When The sTudenTs have a 100 on all The AMES CHAGS and QUICK maTerials They EARN The righT To geT a mini pr39acTice exam To sTudy for The inclass exam FurTher39 incenTive if They geT a 100 on This minipracTice exam BEFORE The in class exam I give Them 5 bonus poinTs on The exam Teaching wiTh Technology 2006 David Toback Texas AampM UniversiTy 2152006 21 AMES Math Strictly limited to the relevant preco requisite math topics for the course Goal quotremindquot students of the tools they should already be really good at and have them practice until they regain facility Studies elsewhere but confirmed here show that students who cannot do well on these quizzes are very unlikely to succeed in the course Encourage them to drop or get other remediation Teaching with Technology 2006 David Toback Texas AampM University 2152006 22 AMES Continued Each quiz is ten multiplechoice problems Have one problem from each of seven areas fractions geometry Trigonometry etc Allow ten minutes to complete the quiz Wellprepared students take about 4 minutes they finish all ten quickly Benefits Effects remediation at the beginning levels the playing field Learn all topics as a whole Doesn39t penalize the less prepared students Establishes high standards No whhhg in class Teaching with Technology 2006 David Toback Texas AampM University 2152006 23 CHAGS Homework System The CHAGS quiz system is different than what most people are used to Common syllabus has homework problems from each chapter for the student to solve For each problem the students are must it on a er using variables previous example BE 0 E going online Same problem is presented on WebCT but with dlfferent numeric parameters Short time to quickl type the new numbers into a calcu ator using their equations on paper and p ug new number into WebCT Teaching with Technology 2006 David Toback Texas AampM University 2152006 24 Example using WebCT 7 573 httpedhrehetvistalamuedu Preview Question Mezilla Firefex YEiF Chapter 4 Preblem 35b New suppese that Darrell Grif th had jumped 24 meters and the time ef the part ef the jump befere his feet left the eer was 044 seeehds what was his auerage aeeeleratieh Ewe yeur answer in miss tn the seeend decimal place assume the aeeeleratieh ef gravity is 980 mfsAE Answer 1 Dane wehetwstatamuedu Teaching with Technology 2006 David Toback Texas AampM University 2152006 25 QUICK After Homework AFTER a 100 on the homework Two or three quick multiplechoice problems they haven39t seen before Use a standard textbook test bank Ten Minutes Have to pick short enough problems New problems for each attempt Teaching with Technology 2006 David Toback Texas AampM University 2152006 26 QUICK Mini PracTice For each exams a minipracTice exam is made from The QUICK quesTions 20 minuTes four problems 5 bonus poinTs for a 100 BEFORE The inclass exam 39 Encourages TimeonTask problem solving preparaTion for The exam Reinforces keeping up wiTh The course conTenT learning maTerial as a whole Teaching wiTh Technology 2006 David Toback Texas AampM UniversiTy 2152006 27 Discussion amp Results History In 2001 there was no webbased learning in the Department Now 13 Homeworks at 10 problemsHW QUICK for each Math quizzes amp MPE Tens of thousands of quizzes per section Most of the tools are now widely adopted by most instructors to some degree gtEasy to incorporate high likelihood of adoption Tzacagrvhecchcoyasesvialneadxs mated 2152006 28 Other Results 700 600 if 500 if 400 if 300 if 200 if 100 if H 1 2 3 4 5 6 7 8 9 10 Attempts per Quiz Quiz Number Students are clearly getting better at the math More than 3 000 math quizzes for 120 students or 300 math problemsstudent Average score for each quiz jumps by 10 Teaching with Technology 2006 David Toback Texas AampM University 2152006 29 First Exam Scores after Math I I I I I I I u I t u I I I u o 20 IlAllstudents e I Students Wlth lt100 on AMES mini practice g exams 310 Compare students who completed math quizzes and those Who didn39t QC 40 60 8C 100 on Scoreonthefirstexam Teaching with Technology 2006 David Toback Texas AampM University 2152006 30 Mini pracTice Exams TudyafTer39 incorporating QUICK quot4 3 Aulstudems miniprac ce exams 1392 Studentswithlt100onQUlCKexam In my course abouT 39 60 of The sTudenTs Take The mini pracTice exam Compare sTudeM Those who did wiTh q 1 Those who didn39T O 39IO 8 6 Number of students O 2 O 40 60 80 39I 00 Score on the second exam Teaching wiTh Technology 2006 David Toback Texas AampM UniversiTy 2152006 31 What we CAN39T claim None of These results grove learning High degree of correlation between good students and likelihood of Taking The mini practice exam in The first place Teaching with Technology 2006 David Toback Texas AampM University 2152006 32 But BUT it does provide a really nice graph to show the students gtEffective motivation quotYou want to do well on the exam Do what the good students do and get a 100 on the practice exam quotYou want to know if you re ready for the exam BEFORE the exam while you can still do some thing about it WebC39T39 will TELL YOU if you are ready and if not which problems you need to study Gives them something to DO Teaching with Technology 2006 David Toback Texas AampM University 2152006 33 Other Observations Surveys results More time spent on roblem solving not memorization amp book rea ing Many InstructorsTeaching Assistants note Clear shift amon weaker students to use symbol based problem so ving methods and selfchecking Marked decrease of student complaints about difficulty following simple math steps Personal Note for my class The 2005 End ofSemester Challenge exam 127 of 581 in my course 22 23 took Challenge Exam 12 from my class 52 even of Top10 scores Eleven of Top15 All are consistent with expectations from the Hterature Teaching with Technology 2006 David Toback Texas AampM University 2152006 34 Conclusions A combined pro ram of inte rating Webbased too s into Intro uctory physics courses Develops math skills Cheaply checks homework with quick feedback Offers LOTS practice problem feedback Pervasively adopted Thousands of quizzes taken Incorporated into the other large courses Appears to have real benefit to students and is readily implemented by new instructors Teaching with Technology 2006 David Toback Texas AampM University 2152006 35 ZZ39nfegrafhg Web Based Teaching Tools info Large UniversiTy Physics Courses David Toback Andreas Mershin and Irina Novikova The Physics Teacher Vol 43 P 594 December 2005 Generous supporT from Instructional Technology Services The DeparTmenT of Physics and The MonTague Scholarship Program aT The CenTer for Teaching Excellence II Teaching wiTh Technology 2006 David Toback Texas AampM UniversiTy 2152006 36 Physics 218 Lecture 1 Dr David Toback Quick Sanity Check Howdy Are you in the right class In froduc an to Classical Mechanics Physics 218 STEPS Physics 218 Lecture I Just getting started I like enjoying class so I39ll work hard for this to be fun tough at 8AM I want everyone to do well and get good grades I39ll also to teach you how to get good grades Still it39s a lot of work We39ll take a jokebreak during class and I39ll show short video clips at the beginning Please send me new material and I39ll do my best to use it in class Physics 218 Lecture I Start with our Thought for The day What it39s like 1390 sit in cm 8AM physics lec rur e H g 39 u gt 39 i mi 39 k w n HF m a i a y V w i 9 s 5 1F i I H 8 1 r A iquot 3915 f r i E a Overview of Today39s Class Syllabus and Other Handouts on my VVebPoge Problem Solving Your homework before next lecture Physics 218 Lecture I 6 Big Picture Textbook Don f Panicquot 5 h Edition There is a both a r39ecitotion and a laboratory for this course First meeting is tomorrow Reoding BEFORE lob Physics 218 Lecture I 7 Handouts on my WebSite By the next class you need to read 39 Laboratory notes WebCT Homework instructions More on this later Frequently Asked Questions FAQ You can also find Exam schedule 39 Lecture notes Physics 218 Lecture I 8 Grades Final 35 3 inclass Exams 13 each HW lec r and reci ra rion Quizzes 20 Laborafory 6 I will curve all The exam scores AFTER The final but will Try To give feedback along The way Most of your grade will be based on your ability 1390 solve problems Physics 218 Lecture I 9 Problem Solving Problem Solving The hearT of This course is problem solving One of The greaT Things abouT The Tebeook is The problems They are ALL imporTanT Spend your Time learning how To solve all of Them They39re hard buT They39re worTh iT Your reward for doing Them You39ll Do well in The course Realize why physics is so inTeresTing Realize why engineering makes you Take This course in The firsT place Problem Solving Feedback This course is designed to help you become an excellenl39 problem solver and give you lots of feedback and help along The way WebCT Reci39l39a39l39ion and Exams will provide feedback Physics 218 Lecture I 12 WebCT and Recitation Problems 39 Math quizzes Using WebCT Are you prepared ma fhema ficaly for the course If not WebCT will tell you where you need help Homework and Hunizzes Will use WebCT to give more feedback Recitation quizzes Work with others to solidify your understanding of the material Physics 218 Lecture I 13 Math and Math Quizzes Studies show that you need To be good of The math To solve physics problems Are you ready for This course Log into WebCT and Take finish your39 math quizzes before Thursday39s lecture These are Timed will Toke of least an hour Bring paper and a pencil Physics 218 Lecture I 14 ExTr39a CrediT When you geT a 100 on all The maTh and HW quizzes for The exam you will EARN THE RIGHT To Take a WebCT mhipr39acfice exam Take as many as you like To sTudy If you geT a 100 before The inclass exam you39ll geT 5 bonus poinTs on The exam One available for each inclass exam TudenTs who do Take iT Typically do 30 poinTs beTTer39 Than Those who don39T Physics 218 LecTure I 15 Speaking of Exams 3 Exams and a Final Closed book formulas if needed will be provided Probems will be very similar to Those on homework and recitation Physics 218 Lecture I 16 Other Requiremen 1395 Requirements In order to pass this course you must Take all the exams and the final Pass the Laboratory Physics 218 Lecture I 18 Due dates coming up 39Week 1 his week Lecture Chapter 1 Reading but nothing due Recitation amp Lab Chapter 1 and Lab 1 AampB Homework due None 39 Week 2 Next week Homework Monday Math quizzes Lecture Chapter 2 Recitation amp Lab Chapter 1 and Lab 2 Week 3 The week after that Homework due Monday Chapter 1 Lecture Chapter 3 amp 4 Recitation Chapter 2 and Lab 3 Etc Physics 218 Lecture I 19 Any Questions I39ve compiled a list of frequently asked question and their answers and put it on my web site You should read that before next class There might be a quiz Physics 218 Lecture I 20 H DVO U39lh JON Download the Laboratory hando Checklist for next time and go to your RecitationLab tomorrow Download the WebCT instructions Get a Neo account if you don39t have one already read your email and log into WebCT Take the free warmup and evaluation quizzes Start finish your math quizzes Read Chapter 1 in the text book Start working on your Ch 1 homework problems Download the Frequently Asked Questions handout and read Can39t remember all this A copy of all my lecture notes are on my website Physics 218 Lecture I 21 NeX l39 Time Next lecture We39ll cover chapter 1 and probably 2 For Next Tuesday Read Chapter 2 Can39l39 remember all This A copy of all my leC39l39ure notes are on my websi39l e Physics 218 Lecture I 22 Physics 218 Lecture 16 Dr39 David Toback Checklist for Today Things The were due Monday Chap39l39er39 8 Quizzes on WebCT Things due 39l oday Read Chapters 10 amp 11 Things That are due tomorrow in Reci39l39a39rion Chap1 er 9 problems Physics 218 Lecture XVI 2 The Schedule This Week 317 Chapter 8 quizzes due in WebCT Reading for Chapters 10 amp 11 Lecture on Chapter 10 11 in recitation Chapter 9 and Exam 2 Review in recitation Next Week 324 Chapter 9 due in WebCT minipractice exam 2 available Exam 2 on Tuesday Recitation on Chapters 10 amp 11 Reading for Chapters 12 amp 13 for Thursday Lecture 12 amp 13 on Thursday Following week Chapter 10 amp 11 material in WebCT Reading Chapters 1416 Lectures on 1416 Lectures 1 and 2 of Four Recitation on Chapters 12 amp 13 Chapter 10 Momentum Want to deal with more complicated systems Collisions Explosions Newton39s laws still work but we need some new ideas Physics 218 Lecture XVI 4 Today39s Lecture Different style than in The Textbook Begin with a definition of Linear Momen fum Then show 39l39ho39l39 conserva on of momenfum helps us solve cer39l39oin Types of problems Things colliding Things exploding Physics 218 Lecture XVI 6 Definition of Linear Momentum Vector equation gt P ml system Physics 218 Lecture XVI 7 Resfm ing Newton39s Second Law quotThe rafe of change of momenfum of an objecf is equal fa fhe nef force appfed f0 if 2F Do a check for cansfanf mass d3 dmV df df m m5 If we exerf a nef force on a body fhe momenfum of fhe body changes Whaf if ZF0P If 27F0 Then dpdf 0 p cons ran39r Mame7 fum does7 139 change e I I i momentum before momentum offer Physics 218 Lecture XVI 9 Conservation of Momentum orasgsem y Newto39s laws F0 Conserva an of Momen fum I Z I I l l i Sum of all Sum of all momentum before momentum after True in X and Y directions separately Physics 218 Lecture XVI 10 Problem Solving For Conservation of Momentum problems 1 BEFORE and AFTER 2 Do X and Y Separately Physics 218 Lecture XVI 11 Psics 218 Lecture XVI 12 Physics 218 Lecture XVI 13 So who 7 Momen39rum is useful when we donquott know anything about The forces Examples from everyday life When ice ska fing if you push someone why do you go backwards Why does a gun recoil when you shoof if Physics 218 Lecture XVI 14 Everyday Experience Question Why do you go backwards when you push someone on fhe ice Newton39s Law39s answer When you exert a force on another person then by Newton39s law The person exerts an equal and opposite force on you Physics 218 Lecture XVI 15 Everyday Experience Cont Question Why do you go backwards 14 en you push someone on the ice Momentum Conservation Answer Before The system starts with zero momentum nobody is moving After The system ends with zero momeh tum you and your friend move 11 030051 te direc tons Physics 218 Lecture XVI 16 Simple Gun Example A gun of mass M5 is sitting at rest with a bullet of mass MB inside i139 You shoot the gun and the bullet comes out with a speed l 0139 angle 8 Whaf is The recoil velocity of the gun Physics 218 Lecture XVI 17 Weird example Ball of mass m is dropped from a heigh l 1 Whaf 12 fhe momen fum before release Whaf 12 fhe momen fum before if hifs fhe ground Is momen fum conserved Physics 218 Lecture XVI 18 What if we add The Earth Whaf 1339 fhe force on fhe ball Whaf 129 the force on the earfh Is fher39e any nef force in 1129 sysfem Is momen fum conserved Physics 218 Lecture XVI 19 Momentum for a system is Conserved Momentum is ALWAYS conserved for o SYSTEM you just have to look at a big enough system to see it correctly Not conserved for a single boll A ball falling is not a big enough system You need to consider what is making it fall Newton39s Law For every action there is an equal and opposite reaction Add up all the momentums in the problem The forcg39 and the forcee Physics 218 Lecture XVI 20 Energy and Momentum in Collisions Definitions 30 11 2 33 Elastic collision kinetic a Approach energy is conserved Inelastic collision kinetic energy is not conserved b comm v l i E E i v 2 Momenfum conserved anaemic Tofa Energy conserved I I v v2 416 6 d If inelastic Physics 218 Lecture XVI 21 Inelastic Collisions By definition Inelastic mechanical energy not conserved kinetic energy not conserved Inelastic Example Two trains which collide and stick together Physics 218 Lecture XVI 22 Colliding Trains 1 Dimension The train car on the lefEt mass m1 is moving with speed V0 when it collides with a stationary car of mass mg The two stick together 1 Whaf 12539 fheir speed affer fhe collision 2 Show that this is inelastic b After collision Physics 218 Lecture XVI 23 Ballistic Pendulum A bullet of ma veloci l39y Va pl a block of M mass M whicl of a pendulum How high I block of W001 Is fhe collision or inelas c Physics 218 Lecture XVI Bottom line When to use Momentum When you don39t know the forces in the system When you are studying all of the pieces of the system which are doing the forcing Before and After Problems Physics 218 Lecture XVI 25 Coming up Yesterday Chapter 8 quizzes in WebCT if you haven39t finished them already Tomorrow Recitation on Chapter 9 and exam review Next Lecture Finish Chapter 10 Next week Homework 9 due Minipractice exam 2 and bonus points Exam 2 Tuesday March 25 h Start Chapters 1216 Physics 218 Lecture XVI 26 Physics 218 Lecture 9 Dr David Toback Checklist for Today Things that were due last Thursday Reading for Chapter 6 Things that were due Monday Chaps 3 and 4 HW on WebCT Things due for Wednesday39s Recitation Problems from Chap 3amp4 Exam review Things for Thursday Study for Exam 1 Minipractice exam for Extra Credit Exam 1 Exam 1 is Thursday during Lecture Formula sheet provided copy on web Topics through Chapter 4 on Syllabus Mostly full length problems with variables Dominated by Chapter 3 amp 4 type problems Today39s lecture not on the exam Physics 218 Lecture IX 3 Other Notes Lab 3 will not be formed during the normal lob time It will not count as part of your physics grade Since you need it for engineering class that class will worth with you to get what you need Physics 218 Lecture IX 4 Overview Today39s lecture is about problem solving for Chapters 5 amp 6 Learn how to use everything we39ve learned so far to solve problems with Rope Friction Physics 218 Lecture IX 5 Rope Problems A PHY218 rope is a perfect rope It is massless and it doesn39t stretch This means The acceleration of any part of a rope is the same as any other part The magnitude of the acceleration of the two things it attaches are egual The tension Force exerted by each end is the same Physics 218 Lecture IX 7 Two Boxes and o Pulley You hold two boxes m1 and m2 connected by a rope Ignore the mass of the running over a pulley at pulley and rope and any rest The coefficient of friction associated with the kinetic friction between puney the table and box I is u You then let go and the mass m2 is so large that the system accelerates Q What is the magnitude of the acceleration of the system Physics 218 Lecture IX 8 Skiing You are The ski designer for The Olympic ski Team Your besT skier has mass m She plans To go down a mounTain of angle 0 and needs an acceleraTion a in order To win The race Whm coef cienr of frl39c on u do her skis need 7 0 have Physics 218 LecTure IX 9 2 boxes connected with a string Two boxes with masses m1 and m2 are placed on a frictionless horizontal surface and pulled with a Force FF Assume the string between doesn39t stretch and is massless a Whaf 39s fhe accelerafbn of fhe boxes b Whaf 39s fhe fenson of fhe sfrhgs befween fhe boxes Physics 218 Lecture IX 10 An Incline a Pulley and two Boxes In the diagram given m1 and ma Ignore the mass of the pulley and cord and any remam cl reSl Kw riction associated with the and the angle 3 is known The r coefficient of I static friction is m and m is known Whaf is ve mass m2 Physics 218 Lecture IX 11 Is if beffer fa push or pull a sled You can pull or push a sled with The same force magnitude FF but different angles 0 as shown in The figures Assuming fhe sled does7739 leave fhe ground and has a cons39anf coefficienf of fric I39on u which is be 39er Physics 218 Lecture IX 12 Coming Up Recitation on Wednesday Exam 1 Preparations Exam 1 on Thursday For Monday Get going on HW5 amp 6 For Lecture next Tuesday Read Chapter 7 39 Later next week Recitation on Chaps 5 amp 6 No Lab Physics 218 Lecture IX 13 Physics 218 Lecture 7 Dr David Toback Before we begin Exam 1 NexT Tuesday Only on Topics Through ChapTer 4 Homework and The Mini pracTice Exam When you have 100 on all of Them you will have access To a mini pr39acTice exam GeT a 100 on The minipracTice exam BEFORE The inclass exam geT 5 bonus poinTs MinipracTice exam is The righT way To sTudy Physics 218 LecTure VII 2 Checklist for Today Things that were due last Thursday Chapter 4 reading Things that are due yesterday Monday WebCT Prelim Math Quizzes Ch2 HW Things that are due today Reading for Chapter 5 For this week andor due next Monday Read Chapter 6 for Thursday Recitation Probs from Chap 3amp4 Lab 3 All Ch3amp4 problems on WebCT due Monday Physics 218 Lecture VII 3 Chapters 5 amp 6 3 Lectures for Chapters 5 amp 6 One lecture on Chapter 5 One lecture on Chapter 6 One lecture on problem solving Lecture Reading Assignments Chap 5 due today Chap 6 due Thursday Today39s lecture not on the exam Physics 218 Lecture VII 4 Overview of Chapter 5 Where we39re going and why Dynamics vs Kinematics Force Newton39s Laws of Motion Normal Force Example problems Note It39s important to be good at ZDimensional motion at this point Physics 218 Lecture VII 5 Where we39re going and why Moving from How things movequot Kinematics To Why things move that wayquot Dynamics Why do you care Different questions Old Whof occelero fion do you need To go from 0 To 60m171r39 in 6 sec New How much force does your car engine need to exert To do if Use all the kinematics vectors and calculus from Chapters 14 Plan Do the concepts then do the problems Physics 218 Lecture VII 7 NewTon39s Lows You shouldn39T memorize Them roTher you need To be able To undersfand and ge Them Don39T wriTe Them down from The overheads They39re in your book We39re going To TronsloTe Them inTo English Big picTure Physics 218 LecTure VII 8 First Concept Whaf is a Force Examples Push Pull Slap Gravity Others Physics 218 Lecture VII Newton39s First Law quotEvery body can finues in it s sfa fe of resf or of uniform speed in a sfr39ayh 7 line unless ac fed on by a non zero nef force Physics 218 Lecture VII 10 Translate That info English Force To cause an aceelera rioh change The veoa ty r39equ l ms 0 Force OI If there is an acceleration 139her39e musf be a net Force 9For39ce is a Vector 9Add up all The forces vectors To find The Net or Total force Newton39s First Law Example of nonzero net forces Fr39iction Makes a moving block a slow down Grovity Makes a ball fall toward the earth Example of zero net force Cor39 just sitting on the pavement No velocity no acceleration mo net force Rocket ship in outer space Nothing to slow it down gt constant velocity gt no net force Physics 218 Lecture VII 12 Newton39s Second Law quotThe accelera an of an ab jecf 12 direc y prapar ana fa fhe ne 7 farce ac ng an if and 12s in versey prapar ana fa ifs mass The direc an of ve accelera an 129 in 1e direc an af fhe nef farce ac an an fhe ab jecf Physics 218 Lecture VII 13 Translate Newton39s Second Law The acceleration is in the SAME direction as the NET FORCE Vecfor Equafion gt This is a VECTOR equation E If I have a force 2F max F may what 129 my a A accelera an Welyhf W my gt More force gt more acceleration gt More mass gt less acceleration Physics 218 Lecture VII 14 Force to stop a car You are a cor designer You must develop a new braking system that provides a constant deceleration Whaf consi cmiL nef force is required fa bring a car of mass m fa resf from a V0V VF0 i gt mm Xg0 XFD Physics 218 Lecture VII 15 Getting to Newton39s Third Law How does one gggz a force Applying a force requires another object A hammer exerts a force on a nail Physics 218 Lecture VII 16 Newton39s Third Law quotWhene ver one ob jecf exerfs a force on a second ob jec f fhe second exerfs an equal and opposife force OR quotTo e very ac fion fhere 129 an equal and opposife reac fion Physics 218 Lecture VII 17 Skater ka rer39 pushes on a wall The wall pushes back Equal and opposite OI CZ f 7 Fame Fame The push from The wall H skim IS a force Force provides an acceleration She flies off with some nonzero speed am 18 wall Walking gt F r39amd an fhe Person ersan an fhe r39ama When you walk you push on The ground and The ground PUSHES you forward Equal and opposite force FGP FPG Physics 218 Lecture VII 19 Normal Force Consider a pen siTTing on a Table Is The force of gm ViTy acTing on iT Is The pen accelera Ting WhaT is The Force WhaT is The difference beTween a force and The NeT Force WhaT keeps The pen from accelera Ting Clearly There is a second force ThaT keeps iT from accelerating Call This The quotnormalquot force Physics 218 LecTure VII 20 Moving towards Problems Done with the concepts for this chapter Overheard quotI understand the concep 7 s buf I can 7 do fhe probems Sigh No exam points for quotcancep 139 you can 7 apply Physics 218 Lecture VII 21 Free Body Diagrams Same tricks as in Chapters 14 1Draw a diaqram Draw each force on an object separately Force diagram 2Break each force into its X and Y components THEN sum Show your TA that you know the difference between a force and a component of force GREAT way to pick up partial credit Physics 218 Lecture VII 22 Pulling a box A box with mass m is pulled along a frictionless horizontal surface with a force F at angle 6 as given in The figure Assume i1 does not leave The surface a Whaf Ils fhe acceerafbn of fhe box bW1af Ils fhe norma force dz jail JQ i K Physics 218 Lecture VII 23 2 boxes connected with a string Two boxes with masses m1 and m2 are placed on a frictionless horizontal surface and pulled with a Force FF Assume the string between doesn39t stretch and is massless a Whaf 39s fhe accelerafbn of fhe boxes b Whaf 39s fhe fenson of fhe sfrhgs befween fhe boxes Physics 218 Lecture VII 24 Rest of This Week Recitation Probems from Chapters 3 and 4 Lab Tensile Strength Reading for Thursday Read Chapter 6 More on force and friction HW3amp4 Due Monday Are you ready for Exam 1 next Tuesday Use WebCT to study Get perfect scores on all Math and HWlHW4 9WebCT minipractice exam becomes available Get a 100 on it BEFORE Tuesdaz s exam and I39ll give you 5 bonus points on the exam Physics 218 Lecture VII 25 Physics 218 Lecture 8 Dr39 David Toback Before we begin Exam is moved to Thursday at 800 AM Formula sheet provided copy on web Topics through Chapter 4 on Syllabus Mostly full length problems with variables Dominated by Chapter 3 amp 4 type problems Today39s lecture not on the exam Physics 218 Lecture VIII 2 Checklist for Today Things that are due Mondax WebCT Prelim Math Quizzes Ch2 HW Things that were due Tuesdax Chapter 5 reading Things that were due Wednesdax Progress on chapter 3amp4 Problems Things that are due Todax Reading for Chapter 6 Next week All Ch3amp4 problems on WebCT Recitation Probs from Chap 3amp4 and Exam revuew Still figuring out lab 3 Physics 218 Lecture VIII 3 Yet more before we begin Minipractice exam available for perfect scores on Ma39rh Quizzes and HW14 5 Extra Credit exam points for a perfect score on The Mini Pr39aC39l39ice BEFORE the exam on Thursday Available now Physics 218 Lecture VIII 4 Chapter 5 amp Chapter 6 Further applications of Newton39s Laws This time Incined Plane Fric1ion Next Time Pr39oblems Physics 218 Lecture VIII 5 Pulling a box A box with mass m is pulled along a frictionless horizontal surface with a force F at angle 0 as given in The figure Assume it does not leave The surface a Whaf is fhe acceemf on of fhe box b Whaf is fhe normal force Physics 218 Lecture VIII Box on an inclined plane A box with mass m is placed on a frictionless incline with angle 00nd is allowed to slide down a What is the normal force 1 What is the acceleration of the box Physics 218 Lecture VIII 8 Friction Two types of friction I Kmefic The friction force that slows things down 2 Static The force that makes it hard to even get things moving Physics 218 Lecture VIII Refrigerator If you push a refryem for when fhere 12539 no fric fion whaf happens In The real world whaf happens Espea aly when 29 fully loaded and on a sficky k fchen floor When does sfa fic fric fion kick in When does kine fic fric fion kick in Physics 218 Lecture VIII 10 Kinetic Friction For kinetic friction it turns out that the larger the Normal Force the larger the friction We can write Here a is a constant Warning THIS IS NOT A VECTOR EQUATION Physics 218 Lecture VIII 11 Static Friction This is more complicated For static friction the friction force can Example of the refrigerator If I don 139 push whaf 12539 fhe sfafZ fric fion force Whaf if I push a liffe Physics 218 Lecture VIII 12 Pulling Against Friction A box of mass m is on a surface with coefficient of kinetic friction y You pull with constant force FP at angle 8 The box does not leave the surface and moves to the right 1 What 2539 the magnitude of the acceleration 2 What angle maximizes the acceleration 13 Exam 1 Results from Previous Semester Over39a Mean5275 or 70 396r39een People who Took The minipractice exam g Mean 56575 or 809 Red People who didn39139 Mean 3875 or 50 Physics 218T0bockpdng 2004 Took Mm Green Mean61 Dia not Red Meon3s C s ores 39mcmae exh39o credit 20 4O 60 80 Exam W Score m nercent WOO Advice Test yourself BEFORE The exam How Get a 100 on The minipractice exam bx xour39self in as few fries gs possible Physics 218 Lecture VIII 14 Next Week Monday Ch3amp4 HW due Monday as exam preparation Don39t forget about extra credit Tuesday Lecture Problems from Chapters 5 amp 6 Wednesday Review for exam Thursday at 800AM Exam Formula sheet provided copy on the web Topics through Chapter 4 on Syllabus Bring your Section Number and UIN to check in your exam Physics 218 Lecture VIII 15 Physics 218 Lecture 15 Dr David Toback Checklist for Today Things due awhile ago Read Chapters 7 8 amp 9 Things that were due Monday Problems from Chap 7 on WebCT Things that are due Yesterday in Recitation Chapter 8 Reading for Lab Physics 218 Lecture XV 2 The Schedule This week 33 Chapter 7 due in WebCT 5 h and 6 h lectures of six on Chapters 7 8 amp 9 Chapter 8 in recitation Nexf week 310 Spring Breakl Following Week 317 Chapter 8 due in WebCT Reading for Chapters 10 amp 11 Lecture on Chapters 10 amp 11 Chapter 9 and Exam 2 Review in recitation Following Week 324 Chapter 9 due in WebCT Exam 2 on Tuesday Recitation on Chapters 10 amp 11 Reading for Chapters 12 amp 13 for Thursday Lecture 12 amp 13 on Thursday

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