Testing What You Know Now

Transcription

1 Tesing Wha You Know Now To bes each you, I need o know wha you know now Today we ake a well-esablished quiz ha is designed o ell me his To encourage you o ake he survey seriously, i will coun as a clicker grade. Also, i can coun as one of he clicker grades you drop. Curren Saus? Goal

2 Please do no wrie on ess. There are 30 quesions. You have ~ 35 min. We will resume class aferward. I will ry o pos hese grades on ecampus his week. You will ge a score of a leas 90 jus for answering all quesions. Every 0.33 poins above ha is one ha you go correc. You are here o learn so don worry if your grade is low.

3 Think abou if you are done wih he survey The speed of a nerve impulse in he human body is abou 100 m/s. If you accidenally sub your oe in he dark, esimae he ime i akes he nerve impulse o ravel o your brain. Draw a picure and lis knowns and unknowns Average velociy = 100 m/s = displacemen / ime Change in ime = = x/v = ~2 m / 100 m/s = 0.02 s or 20 milliseconds

4 Main Ideas in Class Today Graphing: Posiion Velociy v avg = x f f x i i a avg = v f f v i i Acceleraion Pracice ess & key online. Tes 1 over maerial over Chapers 1-3. Pracice Problems: 2.21, 2.25, 2.27, 2.29, 2.31, 2.37, 2.39, 2.43, Concepual Problem 2.9

5 Graphing Posiion, Velociy and Acceleraion y axis = posiion, velociy or acceleraion + You will do hands on graphing work in lab Dependen variable (hing you measure) Independen variable (hing you conrol) x axis = Time (s)

6 Posiion Time Graphs Summarized downward (\)

7 This curve represens he posiion versus ime. Do we know anyhing abou he direcion(s) of moion over he shown ime period? Posiion Time (s)

8 Graphing The blue line shows he posiion of a person a differen imes. When do hey go he fases? Calculae: (i) he velociy of he person as hey moves for 0 o 5 s (ii) Insananeous velociy a 3s (iii) 5 o 7 s (iv) 7 o 9 s (v) Average velociy 0 o 9 s (i) Velociy of he person as hey move from 0 o 5 s = Slope of OA = 0.6 m/s Does his velociy change over ha range? (iii) Velociy from 5 o 7 s = Slope of AB I s he same idea for = 0 m/s calculaing acceleraion from velociy graphs (iv) Velociy from 7 o 9 s = 2 m/s (v) Average velociy from 0 o 9 s= disance/ime=7m/9s=7/9 m/s

9 Noe: If you forge your clicker one day, you may wrie your answers on paper. I will ONLY look a he papers if i migh affec your leer grade a he end of he semeser. A. B. C. D. Q04

10 Velociy Time Graphs Summarized he slope of a velociy-ime graph is he acceleraion horizonal graph segmens indicae ha he objec has consan velociy graph segmens above he x-axis imply movemen in he posiive direcion graph segmens below he x-axis imply movemen in he negaive direcion horizonal segmens on he x-axis indicae no movemen sraigh line graph segmens indicae consan acceleraion (--, / or \) graph segmens moving upward indicae an increase in velociy (/) graph segmens moving downward indicae a decrease in velociy (\) a change of direcion is indicaed whenever he graph crosses he x-axis an increase in speed (magniude of velociy) is indicaed by graph segmens moving away from he x-axis

11 Acceleraion Time Graphs Summarized horizonal graph segmens indicae ha he objec has consan acceleraion a horizonal graph segmen on he x-axis indicaes ha he objec has consan velociy (no acceleraion) graph segmens above he x-axis imply increasing velociies graph segmens below he x-axis imply decreasing velociies no changes in direcion may be inferred from hese graphs A he inroducory physics level, we ypically only deal wih consan acceleraion siuaions, so acceleraion graphs generally consis of horizonal segmens only.

12 An objec is speeding up uniformly in he posiive direcion. Which of he following represens his moion? A. +a B. +a -a -a C. +a D. +a -a -a Q05

13 An objec is speeding up uniformly in he negaive direcion. Which of he following represens his moion? A. +a B. +a -a -a C. +a D. +a -a -a Q06

14 No a graphing quesion, bu he nex par will be This is a moion diagram of an objec moving along he x-direcion wih consan acceleraion. Saring wih 1, he dos 1, 2, 3, show he posiion of he objec a equal ime inervals x = 0 A he ime labeled 3, wha are he signs of he objec s velociy v x and acceleraion a x? A. v x < 0, a x = 0 B. v x < 0, a x > 0 C. v x < 0, a x < 0 D. v x > 0, a x > 0 x E. v x > 0, a x < 0 Q07

15 This is a moion diagram of an objec moving along he x-direcion wih consan acceleraion. Saring wih 1, he dos 1, 2, 3, show he posiion of he objec a equal ime inervals. Q x = 0 Which of he following v x - graphs bes maches he moion shown in he moion diagram? v x v x v x v x x v x 0 A. 0 B. 0 C. 0 D. 0 E.

16 Wha you learn from graphs? Type of graph Posiion vs Time Velociy vs Time Acceleraion vs Time Slope gives: Velociy Acceleraion Change of direcion A maximum or minimum When curve crosses axis --- Can deermine Inegraion (calculus) les you find he area under a curve, bu we won be doing ha

17 Resuls of HW Quesionnaire Many of you hope o learn exacly wha I plan o each! Teach you wha physics is abou Sharpen your analyical hinking skills Simulae your curiosiy abou he world Also prepare many of you for he MCAT/DAT Many people hope o use skills in heir own fields (e.g., occupaional herapy, pharmacy, biology, geology, psychology, exercise physiology)

18 Purpose of he book is o: Provide background for lecures (repeiion) Be a resource for deailed explanaions Our firs es is a week from Friday! Now is he ime o sar geing ready. (such as derivaions of formulas) Be a reference and a sudy guide Offer pracice problems and soluions Help each problem solving To ge an A in his course, i is likely ha you will need o spend >15 hours per week. Don wai unil he es o ge prepared.

19 Clicker Answers Chaper/Secion: Clicker #=Answer Ch.2A: 1=D, 2=E, 3=D, Ch.2B: 4=B, 5=C, 6=A, 7=C, 8=E