Announcemens 9/8/09 1. Course homepage ia: phsics.bu.edu Class web pages Phsics 105 (Colon J). (Class-wide email sen) Iclicker problem from las ime scores didn ge recorded. Clicker quizzes from lecures 1 and will show up as 0 ou of 0 on our grade repor. The won coun agains our free clicker quizzes. 3. econd homework assignmen is due onigh a 11:59 pm. a. If ou missed he firs one, ou do ge hree free lae assignmens (all oher lae work is couned 50%). b. H 3 is due Thursda nigh. 4. am 1 sars Thursda! a. e ll finish up discussing some D kinemaics problems he firs half of Thursda lecure, hen do eam reiew for he second half of he lecure. 5. TA-led eam reiew session Thursda, 7:00-8:30 pm, in C-15 C Reiew quaions For consan acceleraion Three basic kinemaic equaions eloci-ime: posiion-ime: eloci-posiion: ae = 0 + a ( s. = sraigh line) + 1 = 0 + 0 a ( s. = parabola) f 0 + f = 0 = + a Freefall: Penn & Feaher demo Milkdrop demo The Moing Man apple: hp://phe.colorado.edu/new/simulaions/sims.php?sim=the_moing_man Colon - Lecure 3 - pg 1 Colon - Lecure 3 - pg a b Table Tennis c e d Clicker quizzes: There is a lamppos a = 0. hich s cure describes: Q1. a car slowing down as i moes awa from he lamppos Q. a car moes oward he lamppos, bu slows down and urns around and speeds up Q3. a car speeding up as i moes oward he lamppos Q4. a car ha moes awa from he lamppos, urns around and passes he lamppos Ma Lin 008 Olmpic champion Quesion: ha is he direcion of he ball s acceleraion during he conac (hi) beween paddle and ball? A. righ B. lef C. zero Clicker quiz: ha is he direcion of acceleraion of he ball while raeling o he righ, and slowing down due o air resisance? (same choices) Clicker quiz: ha if he ball were ied o a bungee cord conneced o his paddle ha is he direcion of acceleraion a he insan he ball is sopped b he elasic and abou o sar coming back? (same choices) Colon - Lecure 3 - pg 3 Colon - Lecure 3 - pg 4
orked Problem: A rock is hrown upward off a cliff 30 m high, wih an iniial eloci of 0 m/s. a) How long does i ake o reach he op of is pah? b) ha is he eloci jus before i his he ground (30 m below he cliff)? c) How long does i ake o hi he ground? Remember PAuT Vecors: Magniude + Direcion amples: Veloci Acceleraion Displacemen? Posiion? (laer) Forces (in Phsics 106) lecric field, magneic fields More obscure: ind speed Hea flow c. Represened b Arrows Colon - Lecure 3 - pg 5 Colon - Lecure 3 - pg 6 Adding Vecors Graphicall: Tip o Tail Draw he firs arrow saring from he origin Begin he ne ecor saring wih is ail where he ip of he preious ecor leaes off: ip-o-ail Connec up more arrows he same wa, if ou hae addiional ecors o add. The sum is an arrow from he sar of he firs ecor o he end of he las ecor. ample: Add hese wo ecors orked Problem: A suden walks 100 m norh hen 00 m souh-eas. Find her final displacemen ecor relaie o he origin, graphicall. Guidance: A negaie ecor poins in he opposie direcion. Be sure all ecors are drawn o scale From warmup: I doesn' maer which order ou add wo ecors ogeher, ou will ge he same sum eiher wa. a. rue b. false Colon - Lecure 3 - pg 7 Colon - Lecure 3 - pg 8
Relaie elociies From warmup: A man on a readmill is walking a 1.5 m/s o he lef. The readmill is going a m/s o he righ. If ou are sanding sill, i looks like he man is moing: a. 0.5 m/s lef b. 3.5 m/s lef c. saionar d. 0.5 m/s righ e. 3.5 m/s righ Colon s one size fis all relaie eloci equaion a-c = a-b + b-c Read a-c as eloci of objec a wih respec o objec c These are ecors! Problem: A je poined a 100 mph airspeed ( of plane w.r.. air) flies in a 00 mph wind (air w.r.. ground) going. Clicker quiz: ha is he je s rue bearing (eloci wih respec o he ground)? a. b. c. d. In his case man-ground = man-readmill + readmill-ground Quesion: How would ou figure ou he je s oal eloci (magniude)? Colon - Lecure 3 - pg 9 Colon - Lecure 3 - pg 10 Vecor componens Geing ecor from componens: From warmup: Ralph is confused abou how his book defined he componens of a ecor. The book sas, "The componens of a ecor are he projecions of he ecor along he coordinae aes". ha can ou ell Ralph o help him undersand wha he word "projecions" means in his cone? Answer from he class: Colon s adice: hink of shadows hen adding ecors, neer forge his: You can add componens bu ou can add magniudes orked Problem: A bo scou carefull walks norh for 300 m, hen 0 wes of norh for 00 m, hen 40 wes of norh for 400 m. How far from his saring poin is he? ha he angle of his displacemen? Vecor web demo: hp://phe.colorado.edu/sims/ecoraddiion/ecor-addiion_en.hml Geing componens from ecor: Colon - Lecure 3 - pg 11 Colon - Lecure 3 - pg 1
Problem: A capain wans her boa o sail eacl on a map, wih a speed relaie o he earh of 10 mph. ha direcion should she poin her boa if here is a 5 mph curren o he? a. a lile bi norh of eas b. a lile bi eas of norh c. a lile bi souh of eas d. a lile bi eas of souh Hin: ar wih an approimae picure boa-earh = boa-waer + waer-earh D Moion: Basic Concep Moions in perpendicular direcions are independen -direcion = 0 + a 1 = 0 + 0 + a f = 0 + a How fas will he boa hae o go? -direcion = 0 + = f a 1 0 + 0 + a 0 = + a -D Projecile moion: a = 0 a = g projecile: an objec in free fall (= 9.8 m/s ) Colon - Lecure 3 - pg 13 Colon - Lecure 3 - pg 14 Demo: Car & ball Clicker quiz: ha will happen? A. Ball will land in fron of car B. Ball will land in back of car C. Ball will land in car all and Bob each hrow a rock horizonall from a cliff. all hrows her rock hard. Bob hrows his more easil. Clicker quiz: hich spends he longes ime falling? a. all s Demo: hooer & dropper ( balls: one sho & one dropped) Clicker quiz: ha will happen? A. Dropped ball will land firs B. ho ball will firs C. Two balls will land a same ime Clicker quiz: hich rock is going fases (ecor magniude) jus before i his he ground? a. all s Flash animaion: baseball eloci componens hp://sokes.bu.edu/baseball_flash.hml all hrows a rock horizonall from a cliff. Bob hrows his a an angle aboe horizonal. The hrow a he same speed. Clicker quiz: hich his firs? a. all s Colon - Lecure 3 - pg 15 Colon - Lecure 3 - pg 16
From warmup (if we hae ime): hich geomerical shape does a D projecile follow? a. line b. circle c. ellipse d. parabola e. hperbola h is ha? Video: Moorccle jumping oer airplane hp://www.ouube.com/wach?=0p8raga80 Colon - Lecure 3 - pg 17 Colon - Lecure 3 - pg 18