Welcome to Kinematics!

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1 Welcome to Kinematics! Classical Mechanics Mechanics Lecture 1, Slide 1

2 Modus Operandi SmartPhysics Protocol Online Prelectures (animated textbook, before lecture) Online Checkpoints (check knowledge, before lecture) Lectures (very interaccve) Online Homework (first deadline tomorrow, 80% credit for late online homework up to one week from tomorrow, 8am) Mechanics Lecture 1, Slide 2

3 Mechanics Lecture 1, Slide 3

4 Clicker Question 1 Do you have your i>clicker with you today? A) Yes B) No C) Maybe D) I like pudding Mechanics Lecture 1, Slide 4

5 Clicker Question 2 Which of the following best describes your high- school physics class? A) Great B) Pretty good C) So-so D) Not so good E) Awful Mechanics Lecture 1, Slide 5

6 Classical Mechanics Lecture 1 Today's Concepts: a) Displacement, Velocity, AcceleraCon b) 1- D KinemaCcs with constant acceleracon If you haven't done Prelecture 1 yet, please do so later today Mechanics Lecture 1, Slide 8

7 Prelecture Example km 35 km Mechanics Lecture 1, Slide 9

8 Prelecture Example x( t) = x 0 + v avg t = 35 km + 65 km km 35 km 65 km in 1 hour Mechanics Lecture 1, Slide 10

9 Displacement and Velocity in One Dimension Displacement Time taken Mechanics Lecture 1, Slide 11

10 Displacement and Velocity in One Dimension The v(t) vs. t plot is just the slope of the x(t) vs. t plot DefiniCon: Speed = v(t) Mechanics Lecture 1, Slide 12

11 Displacement and Velocity in One Dimension Are the plots shown at the le` correctly related A) YES B) NO Mechanics Lecture 1, Slide 13

12 Clicker Question The velocity vs. Cme plot of some object is shown to the right. Which diagram below could be the Displacement vs. Cme plot for the same object? A B C Mechanics Lecture 1, Slide 14

13 Acceleration Mechanics Lecture 1, Slide 15

14 Checkpoint 1 For the Displacement and Velocity curves shown on the le`, which is the correct plot of acceleracon vs. Cme? A B Mechanics Lecture 1, Slide 16

Typical B answer The velocity starts at a high positive value and then decreases to about zero before increasing again.

15 Clicker Question 4 Vote again A B A B Typical A answer Because a(t)= dv(t)/dt, according to the graph of velocity vs. time, acceleration vs. time graph should be the slope of the velocity vs. time graph. Thus, the answer should be the first graph. Typical B answer The velocity starts at a high positive value and then decreases to about zero before increasing again. Since the velocity graph curves first down then up, the acceleration decreases and then increases instead of just increasing for the entire time. Mechanics Lecture 1, Slide 17

16 Constant Acceleration constant a(t) = a Mechanics Lecture 1, Slide 18

17 Checkpoint 2 At t = 0 a ball, inically at rest, starts to roll down a ramp with constant acceleracon. Suppose it moves 10 cm between t = 0 sec and t = 1 sec. How far does it move between t = 1 sec and t = 2 sec? A) 10 cm B) 20 cm C) 30 cm D) 40 cm E) 60 cm Ramp Demo Mechanics Lecture 1, Slide 19

18 Clicker Question 5? 16ft 9ft 4ft 1ft At t = 0 a ball, inically at rest, starts to roll down a ramp with constant acceleracon. Suppose it moves 1 ft between t = 0 sec and t = 1 sec. How far does it move between t = 1 sec and t = 2 sec? A) 1 ` B) 2 ` C) 3 ` D) 4 ` E) 6 ` Mechanics Lecture 1, Slide 20

Therefore if acceleracon is constant, then velocity will have increased to 2 `/s at 2 seconds.

19 Checkpoint 2 Responses 3 16ft 9ft 4ft 1ft Typical A answer If it moves 1` in 1 sec, using x=x o +vt, v=1/1 or 1m/s. Using v=v o +at, a=1/1 or 1`/s 2. So in the interval of 1 second, the ball will move 1 foot. Typical B answer A B C D E For the first second, the velocity is 1 `/s. Therefore if acceleracon is constant, then velocity will have increased to 2 `/s at 2 seconds. Therefore, in the Cme interval between 2 and 1 seconds, the ball would have moved 2 feet. Typical C answer AcceleraCon is 1 `/s 2 and the velocity at the end of the first interval is 2`/s so at the second interval the distance is 3 ` from the equacon d= v + 1/2 at 2 Mechanics Lecture 1, Slide 21

Welcome to Kinematics!

Welcome to Kinematics! Classical Mechanics Mechanics Lecture 1, Slide 1 Modus Operandi FlipItPhysics Protocol! Online Prelectures (animated textbook, before lecture)! Online Checkpoints (check knowledge,