1. Physics 114A - Mechanics Lecture 3 (Walker: 2.4-5) Velocity & Acceleration January 6, 2011 John G. Cramer Professor Emeritus, Department of Physics B451 PAB jcramer@uw.edu

2. January 6, 2012Physics 114A - Lecture 32/19 Announcements Homework Assignments #1 is now available on WebAssign and is due at 11:59 PM on Thursday, January 12. Assignment #2 is also posted and is due at 11:59 PM on Thursday, January 19. So far 172/216 WebAssign accounts. Obtain a H-iTT clicker from the University Bookstore. We will begin using them for credit next Monday. RF Clickers should be set to Channel 01. Register your clicker using the “Clicker” link on the Physics 114A Syllabus page. So far 121/216 clickers are registered. On January 20 we will have Exam 1. It will be 75% multiple choice and 25% free response. There will be assigned seating. If would like a left-handed seat, an aisle seat, or a front-row seat, send me E-mail with your preference.

3. January 6, 2012Physics 114A - Lecture 33/19 Physics 114A - Introduction to Mechanics - Winter-2012 Lecture: Professor John G. Cramer Textbook: Physics, Vol. 1 (UW Edition), James S. Walker WeekDateL#Lecture TopicPagesSlidesReadingHW DueLab 1 2-Jan-12H1 New Year Holiday No Lab 1st week 3-Jan-121Introduction to Physics1221Chapter 1 5-Jan-122Position & Velocity8222-1 to 2-3No HW 6-Jan-123Velocity & Acceleration10252-4 to 2-5 2 9-Jan-124Equations of Motion9202-6 to 2-7 1-D Kinematics 10-Jan-125Vectors8243-1 to 3-3 12-Jan-126r, v & a Vectors5243-4 to 3-5HW1 13-Jan-127Relative Motion3183-6 3 16-Jan-12H2 MLK Birthhday Holiday Free Fall & Projectiles 17-Jan-1282D Motion Basics5194-1 to 4-2 19-Jan-1292D Examples13224-3 to 4-5HW2 20-Jan-12E1 EXAM 1 - Chapters 1-4 Lecture Schedule (Part 1) We are here.

4. Velocity & Acceleration

5. January 6, 2012Physics 114A - Lecture 35/19 Graphical Interpretation of Average & Instantaneous Velocity

6. January 6, 2012Physics 114A - Lecture 36/19 Velocity & Slope The position vs. time graph of a particle moving at constant velocity has a constant slope. The position vs. time graph of a particle moving with a changing velocity has a changing slope. 3.0 s 4.5 m slope = velocity = 4.5 m/3.0 s = 1.5 m/s

7. January 6, 2012Physics 114A - Lecture 37/19 Constant Acceleration Acceleration characterizes the change in velocity with time:  v/  t. If the acceleration is constant, then the velocity is changing at a constant rate. Graphically, if we plot the velocity vs. time, it will fall on a straight line with a slope determined by the acceleration.

8. January 6, 2012Physics 114A - Lecture 38/19 Acceleration Average acceleration: Instantaneous acceleration: Acceleration units: (m/s)/s = m/s 2

9. January 6, 2012Physics 114A - Lecture 39/19 Position, Velocity, & Acceleration Velocity negative; acceleration negative. Velocity positive; acceleration zero. Velocity positive; acceleration negative. Velocity positive; acceleration positive. Velocity zero; acceleration zero.

10. January 6, 2012Physics 114A - Lecture 310/19 Acceleration Average acceleration: Eqn. (2-5)

11. January 6, 2012Physics 114A - Lecture 311/19 Graphical Interpretation of Average and Instantaneous Acceleration: Acceleration

12. January 6, 2012Physics 114A - Lecture 312/19 Example: An Accelerating Train A train moving in a straight line with an initial velocity of 0.50 m/s accelerates at 2.0 m/s 2 for 2.0 s, coasts with zero acceleration for 3.0 s, and then accelerates at -1.5 m/s 2 for 1.0 s. (a) What is the final velocity v f of the train? (b) What is the average acceleration a av of the train?

13. January 6, 2012Physics 114A - Lecture 313/19 Acceleration (increasing speed) and deceleration (decreasing speed) should not be confused with the directions of velocity and acceleration: Acceleration vs. Deceleration Accelerating Decelerating

14. January 6, 2012Physics 114A - Lecture 314/19 Motion with Constant Acceleration If the acceleration is constant, the velocity changes linearly: (2-7) Constant Acceleration Changing Acceleration Slope ConstantSlope Changing

15. January 6, 2012Physics 114A - Lecture 315/19 Motion with Constant Acceleration Velocity vs. time: (2-7) Average velocity: (2-9) Position as a function of time: (2-10) (2-11) Velocity as a function of position: (2-12)

16. January 6, 2012Physics 114A - Lecture 316/19 Motion with Constant Acceleration The relationship between position and time follows a characteristic curve. Parabola

17. January 6, 2012Physics 114A - Lecture 317/19 Motion with Constant Acceleration

18. January 6, 2012Physics 114A - Lecture 318/19 A park ranger driving at 11.4 m/s in back country suddenly sees a deer “frozen” in the headlights. He applies the brakes and slows with an acceleration of  3.80 m/s 2. (a) If the deer is 20.0 m from the ranger’s car when the brakes are applied, how close does the ranger come to hitting the deer? (b) What is the stopping time? Example: Hit the Brakes!

19. Before Monday, read Walker Chapter 2.6 and 2.7. Register for WebAssign to do homework (so far, 172/216). Homework Assignments #1 is now available on WebAssign. Assignment #1 is due at 11:59 PM on Thursday, January 12. Assignment #2 is also posted and is due at 11:59 PM on Thursday, January 19. Obtain a H-iTT clicker from the University Bookstore. We will begin using them for credit next Monday. RF Clickers should be set to Channel 01. Register your clicker using the “Clicker” link on the Physics 114A Syllabus page (so far 121/216 registered). We’ll test them now. End of Lecture 3