Physics 203 College Physics I Fall 2012

1. Physics 203College Physics IFall 2012 S. A. Yost Chapter 2 Motion in 1 Dimension – Part 2

2. Today’s Topics & Announcements • Constant Velocity Motion • Non-Constant Velocity Motion - Graphical • Constant Acceleration Motion and Falling. • There is a presentation by Dr. Adelman at 6:30 here this evening: Great Astronomical Images. Free DVDs will be distributed after the talk. • You can get some extra participation credit for attending. See me there to be checked off, if you attend.

3. Tuesday’s Assignment • Read Ch. 2, sec. 6 – 7 . We will talk some about section 8, but what we do in class is all you will need. • A quiz on sections 1 – 7 using i>clickers should be anticipated, since we are not having one today. • Also, start reading Ch. 3: at least through sec 2, and to sec. 4 if you can. • Problem Set HW2 is open and due next Thursday. It is mostly on Chapter 2, but includes some trigonometry practice for Chapter 3.

4. Constant Velocity Equation • x = x0 + v t • gives the position as a function of time of an object starting at position x0and traveling with velocity v.

5. Constant Velocity Motion 8 x (m) • A cart goes from x = 2 m at t = 1 s to x = 8 m at t = 3 s at constant velocity. • Draw a graph of the motion. • What is the velocity? 7 6 5 4 3 2 Dx 6 m Dt 2 s 1 v = = = 3 m/s 0 1 2 3 4 -1 t (s)

6. Constant Velocity Motion 8 x (m) • Where was the cart at t = 0? • Linear equation: • x = x0 + v t • Evaluate at any point: • 2 m = x0 +(3 m/s)(1 s) • Solve for x0: • x0 = 2 m – 3 m = – 1 m 7 6 5 v = 3 m/s 4 3 2 1 0 1 2 3 4 -1 t (s) intercept

7. Piecewise Linear Motion What is the displacement from 0 to 8 sec? 8 6 4 2 0 -2 B Dx =-1 m. C A x (m) D t (s) E

8. Piecewise Linear Motion What is the average velocity from 0 to 8 sec? - 8 6 4 2 0 -2 v=-0.125 m/s B C A x (m) D t (s) E

9. Piecewise Linear Motion Distance is the total path-length traveled. 8 6 4 2 0 -2 What is the distance traveled from 0 to 8 sec? B d = 8 + 4 + 7 + 2 m = 21 m C A x (m) D t (s) E

10. Position vs Time Graph Where is the object at rest? 8 6 4 2 0 -2 C B C A x (m) D t (s) E

11. Position vs Time Graph Instantaneous velocity is defined at one time What is the instantaneous velocity at t =1s? 8 6 4 2 0 -2 B v =4 m/s C A x (m) D t (s) E What is the instantaneous velocity at t =3s? v = – 2 m/s

12. Position vs Time Graph Speed is distance traveled divided by the time. Where does the object have the greatest instantaneous speed? 8 6 4 2 0 -2 B D C A x (m) D t (s) E

13. Position vs Time Graph What is that speed? |v|=7.0 m/s 8 6 4 2 0 -2 B C A x (m) D t (s) E

14. Position vs Time Graph What is the average velocity for the first 4 seconds? 8 6 4 2 0 -2 B - v = 4m/4s = 1.0 m/s C A x (m) D t (s) E

15. Position vs Time Graph What is the average speed for the first 4 seconds? 8 6 4 2 0 -2 B |v| = (8+4)m/4s = 3.0 m/s C A x (m) D t (s) E

16. Displacement vs Distance • You and your dog go for a walk to a park. You walk in a straight line while your dog runs back and forth. • When you and your dog arrive at the park, who has the greater displacement? • A. You B. Dog C. Same • Who had the greater average velocity? • A. You B. Dog C. Same • Who had the greater average speed? • A. You B. Dog C. Same

17. Speed vs Velocity • Which does the odometer on your car measure? • A. Distance B. Displacement • Which does the speedometer on your car measure? • A. Speed B. Velocity • Is speed ever negative? • A. Yes B. No • Is velocity ever negative? • A. Yes B. No