Overview Kinemaics: Descripion of Moion Posiion and displacemen velociy»insananeous acceleraion»insananeous Speed Velociy Speed and Velociy Speed & Velociy Velociy & Speed A physics eacher walks 4 meers Eas, 2 meers Souh, 4 meers Wes, and finally 2 meers Norh. Insananeous and Average Insananeous Speed - speed a any given insan in ime Average Speed oal disance divided by oal ime of ravel Insananeous Velociy Insananeous velociy is he limi of he average velociy as he ime inerval approaches 0. I is he insananeous rae of change of posiion wih ime. Insananeous rae of change is he derivaive which means slope of a graph a a poin 1
Acceleraion (m/s/s) The average acceleraion is he change in velociy divided by he change in ime. v() Insananeous acceleraion is limi of average velociy as ges small. I is he slope of he v() plo v() v Acceleraion Unis Speed/ime m/s/s = m/s 2 mi/hr/s = mi/hr-s km/hr/s = km/hr-s Disance/ime/ime or disance/ime 2 31 Acceleraion Slope of V_T Time (s) Velociy(m/s) 0 0 1 10 2 20 3 30 4 40 5 50 Acceleraion Acceleraion is a vecor quaniy defined as he rae a which an objec changes is velociy. An objec is acceleraing if i is changing is velociy. Speeding Up & Slowing Down Posiion vs Time Plos Posiion a =3s, x(3) = 1m Displacemen beween =1s and =3s. x = x (m) 3 Average velociy beween =1 and =3 v = -3 (s) 4 12 2
Which plo bes represens a plo of velociy vs ime corresponding o he posiion vs ime? 1. A 2. B 3. C Acceleraion (m/s 2 ) The average acceleraion is he change in velociy divided by he change in ime. v() v A B C Insananeous acceleraion is limi of average velociy as ges small. I is he slope of he v() plo v() 31 Velociy vs Time Plos Gives velociy a any ime. Area gives displacemen Slope gives acceleraion. Velociy a =2, v(2) = Displacemen beween =0 and =3: =0 o =1: =1 o =3: Average velociy beween =0 and =3? Change in v beween =3 and =5. v = 3 v (m/s) -3 4 Acceleraion Unis Speed/ime m/s/s = m/s 2 f/s/s = f/s 2 mi/hr/s = mi/hr-s km/hr/s = km/hr-s Disance/ime/ime or disance/ime 2 Average acceleraion beween =3 and =5: a = The Ninja Speeding Up & Slowing Down The Ninja moorcycle can accelerae from 0 o 60 mi/h in 3.8 s. Wha is is average acceleraion? 15.8 mi/h/s 23 f/s/s or 7 m/s/s Negaive acceleraion can mean speeding up or slowing down. The same is rue wih posiive acceleraion. 3
Posiion-Time Graphs Consan Acceleraion Which x vs plo shows posiive acceleraion? (A) (B) (C) posiive velociy posiive acceleraion negaive velociy posiive acceleraion negaive velociy negaive acceleraion 1. A 2. B 3. C Summary of Conceps kinemaics: A descripion of moion posiion: displacemen: velociy: average : insananeous: acceleraion: average: insananeous: Posiion Time Consan Acceleraion 50 Consan Posiive Velociy Consan Negaive Velociy 4
Posiive Velociy Posiive Acceleraion Posiive Velociy Negaive Acceleraion Negaive Velociy Negaive Acceleraion Negaive Velociy Posiive Acceleraion Review Kinemaics : Descripion of Moion Posiion Displacemen Velociy»Insananeous Acceleraion»insananeous Equaions for Consan Acceleraion (ex, page 34) v = v 0 + a v av = ½ (v o + v) x = x 0 + v 0 + ½ a 2 v 2 = v 02 + 2a(x-x 0 ) 07 1 0 5
A cheeah can accelerae from res o 25.0 m/s in 6.22 s. Assuming consan acceleraion, A. how far has he cheeah run in his ime? firs find acceleraion A cheeah can accelerae from res o 25.0 m/s in 6.22 s. Assuming consan acceleraion, C. wha is he cheeah s average speed for he firs 3.11 s? hen find disance A cheeah can accelerae from res o 25.0 m/s in 6.22 s. Assuming consan acceleraion, D. calculae he disance covered by he cheeah in he firs 3.11 s. A cheeah can accelerae from res o 25.0 m/s in 6.22 s. Assuming consan acceleraion, afer sprining for jus 3.11 s, he cheeah s speed is 1. < 12.5 m/s 2. = 12.5 m/s 3. > 12.5 m/s A car acceleraes uniformly from res. If i ravels a disance D in ime hen how far will i ravel in a ime 2? 1. D/4 2. D/2 3. D 4. 2D 5. 4D A car acceleraes uniformly from res. If he car has speed v a ime hen wha is is speed a ime 2? 1. v/4 2. v/2 3. v 4. 2v 5. 4v 6