Mechanics Lecture 1, Slide 1 Welcome to Physics 211! Classical Mechanics

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Course Directors  Lecture  Doug Davis  also   Discussion  Robert Chamberlain  Laboratory  Bo Han  Jason Merritt

Course meetings Mechanics Lecture 1, Slide 5

The best way to predict the future is to invent it! — Alan Kay Apple Fellow

Course Structure Spiral Learning  Online Prelectures (animated textbook, before lecture)  Online CheckPoints (check knowledge, before lecture)  Lectures (very interactive, bring notes)***  Online Homework (first deadline this Thursday)  Discussion Section starts this Thursday  Lab Sections start this Wednesday 05

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More about Homework 05 I understand the material. I just can’t do the homework! — James 1:22

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ACT 1 Do you have your i>clicker with you today? A) A) Yes, and I already registered it! B) B) Yes, and I’ll register it tonight! C) C) Yes, but it doesn’t work  D) D) No, but PLEASE give me points anyway! 12

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Prelectures + Checkpoints + Lectures100 Labs150 Hour exams (3 x 100 each)300 Final Exam200 Homework (14) + Quizzes (9)250 Your Grade (see Course Description) 1000 Points You may miss up to 3 Prelectures, Checkpoints and Lectures and still get all 100 points! If you miss a Discussion Quiz, Lab, or Hour Exam due to illness, be sure to fill out an absence form, and bring documentation to 233 Loomis. 14

Q: What are the benefits of participating ? A: You learn more Students who…Exam 1 average Viewed pre-lectures80% Blew through pre-lectures73% What we learned in Physics

Mechanics Lecture 1, Slide 19

Physics 211 Lecture 1 Today's Concepts: a) Displacement, Velocity, Acceleration b) 1-D Kinematics with constant acceleration If you haven't done Prelecture 1 yet, please do so later today 25

Prelecture Example 25

Prelecture Example 26

Displacement Time taken Displacement and Velocity in One Dimension 27

Definition: Speed = |v(t)| The v(t) vs. t plot is just the slope of the x(t) vs. t plot Displacement and Velocity in One Dimension 28

A) YES B) NO Are the plots shown at the left correctly related Displacement and Velocity in One Dimension 30

The velocity vs. time plot of some object is shown to the right. Which diagram below could be the Displacement vs. time plot for the same object? ABC ACT 32

Acceleration 33

For the Displacement and Velocity curves shown on the left, which is the correct plot of acceleration vs. time? A B Checkpoint 1 35

A B For negative t, v(t) is decreasing so its derivative, a(t), must be negative. For positive t, v(t) is increasing so a(t) must be positive. Typical A answer a(t) = slope of v(t).... v(t) decreases then increases (never going negative)... this is confirmed by the displacement graph Typical B answer Vote again ACT 4 37

A ball is thrown straight up in the air. Its position as a function of time is shown in the plot to the right. Which of the following statements is true as the ball goes up? A) A)The acceleration is positive and the ball speeds up B) B)The acceleration is negative and the ball speeds up C) C)The acceleration is positive and the ball slows down D) D)The acceleration is negative and the ball slows down Acceleration ACT 40

Constant Acceleration constant a(t) = a 42

At t = 0 a ball, initially at rest, starts to roll down a ramp with constant acceleration. Suppose it moves 1 foot between t = 0 sec and t = 1 sec. How far does it move between t = 1 sec and t = 2 sec ? A) 1 foot B) 2 feet C) 3 feet D) 4 feet E) 6 feet Ramp Demo Checkpoint 2 45

Using the given information, the ball moves 1 foot in 1 second, so it must be accelerating at a rate of 1 foot per second per second. Between time=1 and time=2 seconds, the ball accelerates to 2 feet per second per second, so it travels 2 feet. Typical B answer when the ball moves one foot during t=0 to t=1 the acceleration is 2. The ball will move 4 feet from t=0 to t=2 with velocity 2. therefore from t=1 to t=2 it will move 4-1=3 Typical C answer Since the ball moves 1 foot between t = 0 and t = 1 at constant acceleration, the ball will move the same distance between t = 1 and t = 2. Typical A answer Checkpoint 2 Responses 50

Using the given information, the ball moves 1 foot in 1 second, so it must be accelerating at a rate of 1 foot per second per second. Between time=1 and time=2 seconds, the ball accelerates to 2 feet per second per second, so it travels 2 feet. Typical B answer when the ball moves one foot during t=0 to t=1 the acceleration is 2. The ball will move 4 feet from t=0 to t=2 with velocity 2. therefore from t=1 to t=2 it will move 4-1=3 Typical C answer Since the ball moves 1 foot between t = 0 and t = 1 at constant acceleration, the ball will move the same distance between t = 1 and t = 2. Typical A answer 1ft 4ft 9ft 3 16ft Checkpoint 2 Responses 50