WebAssgn HW Due 11:59PM Tuesday Clcker Inormaon Remnder: 90% aemp, 10% correc answer Clcker answers wll be a end o class sldes (onlne). Some days we wll do a lo o quesons, and ew ohers Each day o clcker quesons wll be weghed equally wh oher days (no dsadanage rom mssng day wh los) Thus, on days wh los o quesons, each queson wll be worh less. Ahlees/raners wll be ecused rom days n your leers Drop lowes 3 days o clckers.
Reew Tools o he Trade Conerng Uns Dmensonal Analyss Esmaon (no oen) Sgncan Fgures (or homework, usng 3-4 dgs s a good plan)
How do we undersand he moon o a car (and oher su)?
Man Ideas n Class Today Moon n one dmenson Dsplacemen Velocy and Speed Acceleraon Common concerns: nsananeous elocy and acceleraon, speed Era Pracce Problems:.1,.3,.5,.1,.5,.7,.9,.31,.33
Frame o Reerence Descrbes how measuremen o dsplacemen, elocy or acceleraon s made E: Two cars mong n he same drecon a 55 km/hr and 65 km/hr Pro Tp #1: Draw a pcure 55 km/hr 65 km/hr In ground rame o reerence one car moes a +55 km/hr whle he oher moes a +65 km/hr In reerence rame o car on le, elocy o car on rgh s +10 km/hr Generally assume he reerence rame o he Earh (ground rame)
Pro Tp #: Label Frame o Reerence Frame o reerence represened by a coordnae sysem +y 0 + The drecon o hese arrows s mporan or seng up problems and may aec he sgn o your arables and/or answers (wll see eample soon)
Dsplacemen s a ecor. Denon: change n he poson o an objec E: Car nally parked 3.0 m o rgh o house, dres around he block, ends up 5.0 m o le o house. Fnd he dsplacemen o he car. Ths one s easy, bu pracce your pro ps! Fnal poson y Y Pro Tp #3: Ls wha you know n arable orm Inal poson Dsplacemen: Deren reerence rame = -5.0 m X = -8.0 m X = +3.0 m X = 0.0 m = -5.0 m - (+3.0 m) = -8.0 m = -8.0 m (0.0 m) = -8.0 m
Lnkng Your Clcker o he Class Turn on. I doesn say ready or dsplay a check mark, se o class requency AA by holdng down On/O buon and hen press A wce. I wll ery brely dsplay Physcs o ell you ha s good o go. Don orge o regser your clcker hrough ecampus someme hs monh.
Eample Clcker Queson (Ungraded) (Clckers Requred Ne Class) P A bcycls sars a pon P and raels around a rangular pah ha akes her hrough pons Q and R beore reurnng o pon P. Wha s he magnude o her ne dsplacemen or he enre round rp? 400 m 500 m A. 100 m B. 00 m C. 600 m Q 300 m R D. 100 m E. zero Q01
Vecors are ypcally represened as bold. y Fnal poson Inal poson = -5.0 m = +3.0 m = -5.0 m - (+3.0 m) = -8.0 m Noes: 1. Dsance s no dsplacemen. In hs case, dsance raeled s dsance dren around he block. Dsance s always pose, does no ndcae drecon - eample o a scalar. Green arrow rom o ndcaes drecon and magnude o dsplacemen - eample o a ecor 3. Sgn o dsplacemen ndcaes drecon
Flppng he pose drecon can change your answer! Reersng he as y Fnal poson Inal poson + = +5.0 m = -3.0 m = +5.0 m - (-3.0 m) = +8.0 m I we change whch drecon we call pose, hen he orgnal and nal posons change sgn, whch also changes he sgn o he nal dsplacemen. Many people sruggle wh sgn! Takes pracce o maser!
Why would we care abou he sgn? o 1 a a o I you need o use any o hese arables n a ormula, you wll need o use he correc sgn. Many people sruggle wh sgns! Ask yoursel aer denng each arable (p 3) sgn s conssen wh wha drecon you call pose.
Aerage Velocy Denon: elocy s dsplacemen per un me SI uns: m/s E: Go o Psburgh n hrs, back n Morganown 3 hrs aer leang Aerage elocy gong o P: Mo own P = 0 = 0 = +70 m = hrs 0 70 m 70 m 0 hrs 0 35 m/hr
Aerage Velocy Aerage elocy comng back rom P: = +70 m = hrs = 0 m = 3 hrs 0 Mo own P 70 m 0 70 m 3 hrs hrs 70 m/hr Velocy s a ecor. The sgn o elocy ndcaes s raellng along he pose as or n he oppose drecon.
70 m 0 hrs 0 Par 1: Par : 35 m/hr 0 70 m 3 hrs hrs 70 m/hr Wha was he aerage elocy round rp? A. 5.5 mph Mo own P B. 46.7 mph C. 35 mph D. -17.5 mph E. 0.0 mph 0 70 m 3 hour rp Q0
Aerage Velocy Mo own P 70 m 0 hrs 0 0 Par 1: Par : 0 70 m 35 m/hr 70 m/hr 3 hrs hrs Aerage elocy round rp? = 0 m = 0 hrs = 0 m = 3 hrs 0 0 3 hrs 0 0 70 m Noe: Ag. Speed = dsance/me s no he same as elocy. I no drecon change, s he magnude o elocy. Aerage speed round rp = dsance raeled/me:140 m/3 hrs = 47 m/hr
Insananeous Velocy Only use he aerage elocy when asked or aerage. Insananeous elocy s elocy a a parcular nsan. Wll dscuss hs derence more n he graphng secon o Ch..
Acceleraon Aerage acceleraon = change n elocy/me a Insananeous acceleraon a lm 0 Uns: m/s/s = m/s Lke elocy and dsplacemen, acceleraon s a ecor (has drecon and magnude). The sgn o acceleraon ndcaes whch drecon s elocy changes. Pose acceleraon means speedng up when mong n he pose drecon OR slowng down when mong n he negae drecon.
Claryng he Sgns Can someone ge me an eample when an objec s nsananeous elocy and nsananeous acceleraon o be o oppose sgn a some nsan o me? E: car mong n + drecon bu slowng down a +
Le s Do More Pracce The speed o a nere mpulse n he human body s abou 100 m/s. I you accdenally sub your oe n he dark, esmae he me akes he nere mpulse o rael o your bran. Draw a pcure and ls knowns and unknowns Aerage elocy = 100 m/s = dsplacemen / me Change n me = = / = ~ m / 100 m/s = 0.0 s or 0 mllseconds
Acceleraon (Ungraded) Q03 acceleraon = change n elocy oer some me Consder he ollowng suaons: a car slowng down a a sop sgn a ball beng swung n a crcle a consan speed a brang srng (e: plucked guar srng) a person drng down a sragh secon o hghway a consan speed wh her oo on he acceleraor In how many o he suaons s he objec accelerang? A. 0 B. 1 C. D. 3 E. 4
a ag Moon a Consan Acceleraon Specal case when a does no change wh me ag a Noaon: = = 0 = = o = = o o o o ag Smlar deraons lead o more equaons: o o 1 a a o ag o a
Whch ormula o use? o a o a ag o o 1 a Pro Tp #3: Ls wha you know and need o know n arable orm 1 equaon wh one unknown s solable. equaons wh wo unknowns s solable. Pro Tp # 4: Pracce helps you pck bes ormulas!
Plannng a Sraegy A ceran car s capable o accelerang a a rae o 0.60 m/s. How long does ake or hs car o go rom a speed o 55 m/h o a speed o 60 m/h? Draw a pcure and ls knowns and unknowns Wan: Know: o,, a = o +a rearrange: = (- o )/a Wll need o coner m/h o wha?
Whle chasng s prey n a shor sprn, a cheeah sars rom res and runs 45 m n a sragh lne, reachng a nal speed o 7 km/h. (a) Deermne he cheeah s aerage acceleraon durng he shor sprn, and (b) nd s dsplacemen a = 3.5s. o a o a ag o o 1 a
Clcker Answers Chaper/Secon: Clcker #=Answer Ch.A: 1=E, =E, 3=D